The Animal Parasites of Man (part 2 of 6)

Appendix

“Rhizopods in Poliomyelitis acuta.”

In three cases of poliomyelitis acuta which were investigated by Ellermann, the spinal fluid obtained by puncture of the cord contained bodies, from 10 µ to 15 µ in size, which had amœboid movements and exhibited variously shaped pseudopodia in large numbers. After staining, a usually excentric nucleus, about 1·5 µ in size, was demonstrated in them.

Order. *Foraminifera*, d’Orbigny.

The order is divided by Max Schultze into Monothalamia and Polythalamia. Only a few of the former can be considered here.

Sub-Order. *Monothalamia.* (Testaceous Amœbæ).

These forms occur frequently in fresh water, rarely in sea water. They possess a shell which is either pseudo-chitinous in character, or consists of foreign particles, or in a few cases is composed of siliceous lamellæ. There is usually an orifice for the protrusion of pseudopodia. The only representative of the order of interest here is:--

Genus. *Chlamydophrys*, Cienkowski, 1876.

The genus is based on a form which A. Schneider carefully investigated and considered to be the Difflugia enchelys of Ehrenberg. L. Cienkowski rediscovered this same form and created for it the genus Chlamydophrys. We agree with this view, but not with the renaming of the organism (so common at the time). If the parasite in dung, Chlamydophrys stercorea Cienk. is identical with Difflugia enchelys of Ehrenberg, the old specific name should be retained.

The genus is characterized by the possession of a hyaline, structureless, slightly flexible shell which is ovoid or reniform. At the more pointed pole there is an orifice situated terminally or somewhat laterally, serving for the emergence of the filiform pseudopodia (fig. 13, a). The protoplasm does not entirely fill the interior of the shell. An equatorial zone bearing excretory granules divides the shell internally into two almost equal portions. The anterior portion is rich in vacuoles and serves for the reception of nutriment and for digestion. The posterior part is vitreous, and contains the nucleus. One to three contractile vacuoles are situated in the equatorial zone.

*Chlamydophrys enchelys*, Ehrbg.

Syn.: Chlamydophrys stercorea, L. Cienkowski.

This species (fig. 13) is found in the fæces of various animals (cattle, rabbits, mice, and lizards), and also in quite fresh human fæces. According to Schaudinn, the parasite occurs so frequently in the human fæces that it must be considered of wide distribution. The species must traverse the intestine of man and animals during one stage of its life cycle, as Schaudinn showed by experiments on himself and on mice. He infected himself with cysts (fig. 14) by swallowing them, and evacuated the first Chlamydophrys as early as the following day. After the evacuation of numerous specimens on one of the following days the infection ceased.

The nucleus of a living specimen is surrounded by a hyaline, strongly refractile chromidial mass, arranged in the form of a ring. Chromatin stains colour it darkly.

Asexual multiplication (fig. 13, b), which takes place in fæces, follows a similar course to that of allied forms (e.g., Euglypha, Centropyxis). It commences by the cytoplasm issuing from the orifice of the shell and assuming the shape characteristic of the mother organism, but in a reverse position. The nucleus then divides by mitosis, when the daughter nuclei move apart from one another. The chromidial ring also divides into two portions by a process of dumb-bell like constriction. The one daughter nucleus remains in the mother organism, the other moves towards the daughter individual, which then separates from the parent.

In this species plasmogamic union of two or more individuals (up to twenty) is frequently observed. Such colonies may similarly divide, and in this way monstrosities frequently arise. When drying of the fæces, or deficiency of food occurs, encystment takes place apparently spontaneously. The whole body, as stated by Cienkowski, issues from the shell, assumes a spherical shape (probably with discharge of water) and becomes surrounded with a thick membrane (fig. 14). After the addition of water and the escape of the encysted Chlamydophrys, a new shell must be formed. Schaudinn, who has not given a more detailed description of the process of encystment in this species, but refers to Cienkowski and to similar observations made on Centropyxis, states of the latter that the encystment takes place within the shell.

The sexual multiplication is accompanied by shedding of all the foreign bodies and of the degenerating nucleus. The protoplasm, now contracting into a sphere, remains behind in the shell with the chromidial mass. From the latter several new nuclei arise (sexual nuclei) often eight in number. The cytoplasmic sphere then segregates into as many spherical portions as there are nuclei present. When they have assumed an oval form, two flagella develop at one pole and the flagellispores swarm out of the shell.[35] The biflagellate swarm-spores, or gametes, copulate in pairs and apparently the individuals of the pairs of gametes arise from different mother organisms. The zygote secretes a thick covering which soon becomes brown and rough. These zygote cysts or resistant spores must now pass from the intestine of an animal in order to complete their development. The escape of the cyst contents does not always take place in the intestine; often it does not occur until after defæcation. These shell-less individuals (amœbulæ) soon become invested with a shell. But in the alkaline intestinal contents, shell formation may proceed even while the organism is in the intestine, and multiplication may take place.

[35] Schaudinn (1903), Arb. a. d. Kaiserl. Gesundh., xix, p. 547.

Schaudinn’s further communication was of special interest; it was to the effect that Chlamydophrys was related to

*Leydenia gemmipara*, Schaudinn, 1896.

In the fluid removed by puncture from two patients suffering from ascites in the first medical clinic in Berlin, cellular bodies with spontaneous movement were found, which Leyden and Schaudinn regard as distinct organisms. They remained alive without the use of the warm stage for four or five hours, the external temperature being 24° to 25° C. In a quiescent condition they were of a spherical or irregular polygonal form. Their surface was rarely smooth, being beset with protuberances and excrescences (fig. 15). The substance of the body was thickly permeated with light refractile granules with a yellowish shimmer. The hyaline ectoplasm was rarely seen distinctly. All sizes from 3 µ to 36 µ in diameter were observed. The movements were rather sluggish, the ectoplasm in the meantime appearing in the form of one or several lamellæ, in which also strings of the granular endoplasm occurred, and frequently protruded over the border of the hyaline pseudopodia. The tendency for the joining of several individuals by means of their pseudopodia was so marked that associations ensued similar to those known in free-living Rhizopoda.

The cytoplasm enclosed blood corpuscles as well as numerous vacuoles, one of which pulsated slowly about every quarter of an hour. A vesicular nucleus the diameter of which was about equal to one-fifth of the body was present.

Multiplication took place by means of division and budding (fig. 15, c), after previous direct division of the nucleus. The buds were supposed to divide repeatedly soon after their appearance, thus giving rise to minute forms of 3 µ.

There was a suspicion in both cases that the ascites was associated with malignant neoplasms in the abdomen, and autopsy confirmed this view in one case.

The parasite, which has seldom been observed, has been variously interpreted; for example, it has been regarded merely as altered tissue cells. It is now known, from Schaudinn’s researches, that Leydenia gemmipara is connected with abnormal conditions of Chlamydophrys, occasionally occurring as a commensal in the ascitic fluid. The form is produced when pathological conditions of the large intestine create an alkaline reaction of its whole contents. The formation of shells then often ceases, and these naked Chlamydophrys are enabled to multiply atypically by division and gemmation. Such stages, which are no longer capable of a normal development, are the Leydenia, as Schaudinn has demonstrated.

Class II. *MASTIGOPHORA*, Diesing.

Sub-Class. FLAGELLATA, Cohn emend. Bütschli.

During the motile part of their life the Flagellata possess one or more flagella which serve for locomotion, and in many cases also for the capture of food. A few groups (Euglenoidinæ, Choanoflagellata) have only one flagellum, others two or several of about equal length (Isomastigoda), or of various lengths (Monadina, Heteromastigoda, Dinoflagellata). The long flagellum is the principal one; the smaller ones on the same organism are accessory flagella. The flagella directed backwards, which occur in the Heteromastigoda and are used for clinging, are termed trailing flagella or tractella. At the base of the flagellum, which is almost always at the anterior end, a Choanoflagellate possesses a cytoplasmic funnel-shaped neck or collar. In the parasitic forms an undulating membrane is often present.

The body of the Flagellata is usually small, generally elongate and of unchangeable form. It is frequently covered by a distinct cuticle, and, in certain groups, by a hard envelope, or it may be more or less loosely enveloped by a gelatinous or membranous covering. An ectoplasmic layer is thin and not always obvious. The granular cytoplasm contains a varying number of vacuoles, one of which may be contractile, and is generally situated near the area from which the flagella arise, that is, at the anterior extremity. The cytoplasm, moreover, contains the nucleus, which is nearly always single; and in many species there are also yellow, brown, or green chromatophores of various shapes, such as occur in plants. Some species feed after the manner of green plants (holophytic), or of plants devoid of chlorophyll (saprophytic); others, again, ingest solid food, and for this purpose usually possess a cytostome; the latter, however, in a few forms is not used for its original function, but is connected with the contractile vacuole. Many parasitic forms feed by endosmosis. A few species possess eye-spots with or without light-refracting bodies.

Variation in the form of the nuclear apparatus occurs. One nucleus only, which may be compact or vesicular, is known in many species. This nucleus is situated either centrally or sometimes near the flagellar end of the body, but its position is subject to variation. The flagella may arise near the nucleus. Other structures, such as an axial filament and a rhizoplast, may be present. Some flagellates are binucleate, the two nuclei--which often differ in size and shape--being separated from each other. One of these nuclei is the principal, vegetative or trophic nucleus; the other is an accessory nucleus, frequently termed the blepharoplast, flagellar or kinetic nucleus. One or more small basal granules are often present at or very near the origin of the flagella.

Multiplication is by fission, usually longitudinal, which may occur in either the free or encysted forms. Division is initiated by that of the nucleus or nuclei (especially the kinetic nucleus). The basal granule divides also. Collars and chromatophores, if present, likewise separate into two. Variation in the method of doubling the original number of flagella occurs. In most organisms, especially uniflagellate forms, the flagellum splits lengthwise, after division of the basal granule, blepharoplast and nucleus. The daughter flagella may be of the same or different lengths and thicknesses. Other flagellates at division are said to produce new flagella in the neighbourhood of the original ones. The daughter organisms in such cases are provided with one or more parental flagella in addition to newly formed ones. It has been stated that in certain cases the parent flagellate retains all its flagella, while new ones arise ab initio in the cytoplasm of the daughter forms.

Multiplication by longitudinal fission may be interrupted sooner or later by the production of gametes, which form zygotes, from which new generations of individuals arise. In many flagellates gamete formation and sporogony are unknown, and asexual reproduction by fission alone prevails.

Incomplete division results in the formation of colonies of individuals. These colonies must not be confused with the aggregation rosettes of flagellates found among the parasitic Mastigophora. The individuals of aggregation rosettes are capable of immediate separation from the rosette at will.

A number of parasitic Flagellata produce non-flagellate stages which are very resistant to external conditions, the assumption of which forms serves to protect the organisms during their transference from one host to another. Such non-flagellate forms possess one or more nuclei, are usually of an oval or rounded contour, and are capable of developing into the full flagellate on the return of more favourable conditions. These forms are often known as the post-flagellate stage of the organism. When ingested by a new host, the post-flagellate coat becomes more flexible, and the phase of the organism which now recommences growth is known as the pre-flagellate stage; it gradually develops into the typical flagellate organism.

Many Flagellata live free in fresh and salt water. They prefer stagnant water, rich in organic products of decomposition, such as puddles, swamps and pools. Those forms developing shells and colonies are, as a rule, adherent. A number of species are parasitic in man and animals, living mostly within the intestine or in the blood.

It is usual to classify the Flagellata in four orders: Euflagellata, Dinoflagellata, Choanoflagellata, and Cystoflagellata, of which only the Euflagellata are of interest to us. This is a group comprising numerous species, for the further classification of which the number and position of the flagella are utilised.

The Euflagellata observed in man belong to the Protomonadina as well as to the Polymastigina. The former possess either only one or two similar flagella, or one principal and one or two accessory flagella. The Polymastigina possess at least three flagella of equal size, or four to eight of unequal size, inserted at different points. An undulating membrane may be present in members of both groups.

It must also be pointed out that unicellular organisms with one or several flagella are not always classified with flagellates, for such forms occur in Rhizopods as well as temporarily in the lower plants. In addition, the examination of the flagellates, especially the parasitic species, is very difficult on account of their diminutive size and great activity; thus it happens that certain forms cannot with certainty be included in the group because their description is insufficient.

Order. *Polymastigina*, Blochmann.

The Polymastigina contains flagellates with three to eight flagella. Some of the Flagellata parasitic in man belong to the Polymastigina, and to two or three genera that are easily distinguishable.

Genus. *Trichomonas*, Donné, 1837.

The body is generally pyriform, the anterior part usually rounded, the posterior part pointed. There are at the anterior extremity three (? four) equally long flagella that are sometimes matted together. A blepharoplast (kinetic nucleus) and basal granule are present, together with a supporting structure known as an axial filament or axostyle. In addition there is an undulating membrane, bordered by a trailing flagellum, that commences at the anterior extremity and proceeds obliquely backwards. The nucleus, which is vesicular, is situated near the anterior extremity, and behind it are one or more vacuoles, none of which seems to be contractile. These flagellates are parasitic in vertebrate animals, and live chiefly in the intestine.

*Trichomonas vaginalis*, Donné.

The form of the body is very variable, and is elongate, fusiform or pear-shaped, also amœboid. The length varies between 15 µ and 25 µ, and the breadth between 7 µ and 12 µ. The posterior extremity is drawn out to a point and is about half the length of the remainder of the body. The cuticle is very thin and the body substance finely granular. At the anterior extremity there are three--some say four[36]--flagella of equal length which are frequently united together, at least at the base, and are easily detached.

[36] To explain this discrepancy it is stated that the border of the undulating membrane can be detached in the form of an independent flagellum. But Parisi (1910) places such quadriflagellate forms in the sub-genus Tetratrichomonas, Arch. f. Protistenk., xix, p. 232.

There is an undulating membrane (fig. 16) which runs spirally across the body, arising from the place of insertion of the flagella, and terminating at the base of the caudal process. A cytostome seldom is recognizable in fresh specimens, but is apparently present. The nucleus is vesicular, elliptical and situated near the anterior extremity.[37]

[37] According to Marchand, the nucleus is connected with a line, which becomes visible on addition of acetic acid, terminates at the posterior extremity, and does not correspond to the line of insertion of the undulating membrane. This formation probably is the same as the axostyle in Trichomonas batrachorum, Perty. Blochmann (1884) also mentions two longitudinal rows of granules, which commence at the same place as the nucleus and converge posteriorly.

Multiplication takes place by division (Marchand). Encysted forms are almost unknown.

Trichomonas vaginalis lives in the vaginal mucus of women of various ages, not in normal mucus, but in mucus of acid reaction. It is found in menstruating females as well as in females who have passed the menopause. It occurs in pregnant and non-pregnant women, even in very young girls, provided always that they have a vaginal catarrh with acid reaction of the secretion. Should the acid reaction change, as, for instance, during menstruation, the parasites disappear, as they do likewise on injection of any alkaline fluid into the vagina. A low temperature (below +15° C.) is also fatal to the parasites. These flagellates can pass from the vagina through the urethra into the bladder, and produce severe catarrh, and are not easily removed.

T. vaginalis appeared to be a parasite specific to the female organs and not transmissible to man. However, several observations have since been made that confirm the occurrence of this species in the urethra of the male. The infection apparently takes place through coitus when changes are present in the urethral mucous membrane. At any rate, three cases observed point to this circumstance.

Attempts at experimental transmission to rabbits, guinea-pigs and dogs failed (Blochmann, Dock). So far, the manner in which women become infected is unknown.

*Trichomonas intestinalis*, R. Leuckart, 1879 = *Trichomonas hominis*, Davaine, 1854.

Some authors believe that a second trichomonad inhabiting man, Trichomonas intestinalis, R. Lkt., is identical with Trichomonas vaginalis, Donné. Leuckart’s species was based on the discoveries of Marchand (1875) and Zunker (1878), who stated that according to all appearances, and in their opinion, it was the same as Cercomonas intestinalis, Lambl, 1875 (nec 1859), which they found in the fæces of patients suffering from intestinal disorders. The organism is described by them as being pear-shaped and 10 µ to 15 µ in length and 3 µ to 4 µ in breadth. The posterior extremity terminated in a point (fig. 17).

A row of twelve or more cilia was said to commence at the anterior end and extend over the body. Leuckart stated that this parasite, placed by the two authors in the genus Cercomonas, was a Trichomonas, and that they mistook the undulating membrane for cilia, and overlooked the flagella. Notwithstanding its striking similarity with T. vaginalis, it was said to be distinguishable from that species by differences in the undulating membrane. Lambl’s C. intestinalis[38] (of 1875) which corresponds with C. hominis, Davaine[39] (1854), is regarded by Leuckart as a true Cercomonad (characterized by a flagellum and the absence of an undulating membrane, see p. 61), and is thus generically distinct from Trichomonas.

[38] Under the term Cercomonas intestinalis, Lambl in different years has described two entirely distinct Flagellata, namely, in 1859 (“Mikr. Unters. d. Darm- Excrete,” Prag. Vierteljahrsschr. f. prakt. Hlkde., lxi, p. 51; and Lambl, A. d. Franz-Josephs-Kinderspitale in Prag, Prag, 1860, i, p. 360), a form that at the present day is termed Lamblia intestinalis; and in 1875 (in the Russian Medical Report, No. 33), a species identical with Cercomonas hominis, Dav.

[39] Davaine, C., “Sur les anim. infus. trouv. dans les selles d. malad. atteints du cholera et d’autr. malad.,” C. R. Soc. Biol., 1854, ii, p. 129.

The correctness of Leuckart’s judgment in regard to Marchand-Zunker’s flagellate was demonstrated by Grassi’s researches, accounts of which were published soon after. In about 100 cases of bowel complaints in North Italy and Sicily, Grassi found Flagellata in the stools, which he first named Monocercomonas and Cimænomonas, but later termed Trichomonas. However, in opposition to Leuckart, Grassi has also classified Davaine’s C. hominis (= C. intestinalis, Lambl, 1875) as Trichomonas, and most authors have followed his example. Hence arose the use of the name Trichomonas hominis. It was through Janowski (1896) that the former view was again taken up. After a review of the literature, the occurrence of Cercomonads in the intestine of human beings in addition to Trichomonads was considered by the author to have been proved, and he added a description of the Trichomonads. According to this, all morphological distinction between T. vaginalis, Donné, and T. intestinalis, Leuckart, disappeared. On the other hand, it is worthy of note that the smaller size, the more pear-shaped form, and the longer flagella differentiate T. intestinalis (= T. hominis) from T. vaginalis.[40]

[40] For the present the following should be regarded as synonymous: Protoryxomyces coprinarius, Cunningham (Quart. Journ. Micr. Sci. (2) 1880, xxi, p. 234), (Zeitschr. f. Biol., 1882, viii, p. 251). Monocercomonas hominis, Grassi, 1882. Cimænomonas hominis, Grassi, 1882. Trichomonas hominis, Grassi, 1888. Cercomonas coli hominis, May (Deutsches Archiv. f. klin. med., 1891, xlix, p. 51). Monocercomonas hominis, Epstein (Prag. med. Wochenschr. 1893, Nos. 38–40). Trichomonas confusa, Stiles (Zool. Anz., 1902, xxv, p. 689). Trichomonas elongata, Trichomonas elliptica, Cohnheim (Deutsche med. Wochenschr., 1903, xxix, Nos. 12–14). Trichomonas elongata, Trichomonas caudata, Trichomonas flagellata, Steinberg (Kiewer Zeitschr. f. neuere Medicin, 1862). Trichomonas pulmonalis, A. Schmidt, (Münch. med. Wochenschr., 1895, No. 51), and St. Artault (Arch. de parasit. 1898, i, p. 279).

The easily deformed pear-shaped body has three free flagella anteriorly, and an undulating membrane with its flagellar border terminating in a short free flagellum posteriorly (figs. 17, 18). The undulating membrane may coil itself spirally round the body. A supporting rod or axostyle projects as a posterior spine. It appears to begin near the nucleus and blepharoplast, which are situated near the more rounded, anterior end of the body. There may be a chromatoid basal supporting line along the body for the undulating membrane. Rows of chromatoid granules are sometimes situated along one side of the axostyle. A cytostome may sometimes be seen. In mice, Wenyon (1907) found these parasites to vary in length from 3 µ to 20 µ. They occur in the cæcum and intestine of mice, where their internal structure seems more obvious than in man. The flagellates divide by longitudinal fission.

T. intestinalis, R. Leuckart, appears to be capable of settling in all parts of the human intestine in which the contents have an alkaline reaction. Trichomonads have been cited as occurring in the oral cavity by Steinberg, Zunker, Rappin and Prowazek; in the œsophagus by Cohnheim, and in the stomach by Strube, Cohnheim, Zabel, Hensen and Rosenfeld. The normal situation seems to be the small intestine. The parasites then appear in the dejecta, especially in various intestinal diseases the course of which is connected with an increased peristalsis. They are also found in healthy persons, from whom they are obtained after the administration of laxatives. They have been regarded by some workers as commensals, which, however, have the power of accelerating the onset of intestinal complaints, or at least of adding to them. They have been found in cases of carcinoma of the stomach, and in other diseases of that organ in which the acid reaction ceased.

Naturally, whether all the reports relate to the same species of Trichomonas must remain undecided. Certain authors (Steinberg, Cohnheim, van Emden) accept several species. Prowazek speaks of a variety of T. intestinalis inhabiting the oral cavity. This was distinguished by a posterior process exceeding the length of the body fourfold, and by a somewhat unusual course of the undulating membrane. The food of this form, which was found in the whitish deposit present, especially in the cavities of carious teeth, consisted almost exclusively of micrococci. Schmidt and St. Artault named the Trichomonads found in pathological products (e.g., gangrene, putrid bronchitis, phthisis) of the lungs of man, as Trichomonas pulmonalis. Trichomonads have also been found by Wieting in lobular pneumonia in the lungs of pigs.

It is still uncertain in what way the infection takes place. Experiments in the transmission of free trichomonads to mammals (per os), in which the same or allied species occur (guinea-pigs, rats, apes), have been without result. Probably encystment is necessary. Such conditions are mentioned by May, Künstler, Roos, Schurmayer, van Emden, Prowazek, Galli-Valerio and Schaudinn. According to Prowazek, intestinal trichomonads of rats become encysted for conjugation. In the cyst an accumulation of reserve food material occurs, causing distension. The nuclei of the conjugants each give off a reduction body and, after fusion, produce the nuclei for the daughter individuals. According to Schaudinn the intestinal trichomonads lose their flagella before conjugation, become amœboid and encyst in twos, the formation of a large agglomeration of reserve substance accompanying this. Galli-Valerio found double-contoured cysts in the fæces of trichomonad-infected guinea-pigs, after the fæces had been kept for a month in a damp chamber. When exposed to heat small flagellates escaped from them. Administration of such material containing cysts resulted in severe infection with trichomonads, and death of the experimental guinea-pigs followed. The cyst wall is clearly a protection against the deleterious acid reaction of the stomach contents. Alexeieff (1911) and Brumpt (1912) think that the trichomonad cysts of man are really fungi, while other workers also doubt encystment among trichomonads. Wenyon (1907) states that T. intestinalis in mice produces spherical contracted forms which escape from the body in the fæces.

Air, water, and under certain circumstances even food may be regarded as vectors for the trichomonads. The occurrence of the organisms in the oral cavity, and still more so in the lungs, is in favour of the air being the transmitting agent. An observation made by Epstein supports the idea of water transmission. Multiplication of the trichomonads, once they have gained access to the body, is effected by longitudinal division commencing at the anterior end (Künstler). “Cercomonads” with several flagella and an undulating membrane, as well as trichomonads, have been observed by Ross in some cases of cutaneous ulcers.

Mello-Leitao (1913)[41] has described flagellate dysentery in children in Rio de Janeiro. He states that it is due to T. intestinalis and Lamblia intestinalis either separately or together. Flagellate dysentery, he thinks, is benign and is the most frequent form of dysentery in infants. The flagellates are pathogenic to infants under three years of age. Escomel (1913)[42] found 152 cases of dysentery in Peru due solely to Trichomonas. Such cases are probably widespread.

[41] Brit. Journ. Children’s Diseases, x, p. 60.

[42] Bull. Soc. Path. Exot., vi, p. 120.

Genus. *Tetramitus*, Perty, 1852.

*Tetramitus mesnili*, Wenyon, 1910.

Syn.: Macrostoma mesnili, Chilomastix mesnili, Fanapapea intestinalis.

The genus Tetramitus differs from Trichomonas in possessing an undulating membrane inserted in a deep groove or cytostome. There are three anterior flagella. The pear-shaped organism measures 14 µ by 7 µ, but smaller examples occur. T. mesnili occurs in the human intestine, having been described by Wenyon[43] (1910) from a man from the Bahamas in the Seamen’s Hospital, London. Its occurrence is widespread. Alexeieff considers that Macrostoma and Tetramitus are synonymous. The parasite is the same as Fanapapea intestinalis, Prowazek, 1911, from Samoa. Brumpt (1912) found T. mesnili to be the causal agent of colitis in a Frenchwoman. Nattan-Larrier (1912) considers it of little pathological importance.

[43] Parasitology, iii, p. 210.

Gäbel[44] (1914) described an interesting case of seasonal diarrhœa acquired in Tunis, in which a new Tetramitid was the causal agent. The organism was pear-shaped, without an undulating membrane, and measured 6·5 µ to 8 µ by 5 µ to 6 µ. The cytostome was large, and there was no skeletal support. Encystment occurred. Gäbel named the organism Difämus tunensis and considered that it was pathogenic.

[44] Arch. f. Protistenk., xxxiv, p. 1.

Genus. *Lamblia*, R. Blanchard, 1888.

Syn., Dimorphus, Grassi, 1879, nec Haller, 1878; Megastoma, Grassi, 1881, nec de Blainville.

The body is pear-shaped, with a hollow on the under surface anteriorly. It has four pairs of flagella directed backwards, of which three pairs lie on the borders of the hollow disc, and the fourth arises from the pointed posterior extremity.

*Lamblia intestinalis*, Lambl, 1859.

Syn.: Cercomonas intestinalis, Lambl, 1859 (nec 1875); Hexamitus duodenalis, Davaine, 1875; Dimorphus muris, Grassi, 1879; Megastoma entericum, Grassi, 1881; Megastoma intestinale, R. Blanch., 1886; Lamblia duodenalis, Stiles, 1902.

The organism is pear-shaped and bilaterally symmetrical. It is from 10 µ to 21 µ long and 5 µ to 12 µ broad and possesses a thin cuticle. Anteriorly an oblique depression is present, which functions as a sucking disc (fig. 19, s). Its edges are raised above the general surface and are contractile. It corresponds to a peristome and acts as an adhesive organ (fig. 20, b, c). No true cytostome is present. A double longitudinal ridge, representing axostyles, extends from the sucking disc to the tapering posterior extremity, which is prolonged as two flagella from 9 µ to 14 µ long.

Lamblia intestinalis possesses eight flagella (fig. 19). The first pair of flagella, which cross one another, arise in a groove formed by the anterior edge of the sucking disc. Two pairs of flagella (lateral and median) are inserted on the posterior edge of the disc, while the posterior flagella occur at the tapering posterior extremity of the body. Basal granules are found at the bases of the flagella. The median flagella are most active in movement, the anterior and lateral flagella being less motile, as they are partially united to the body for part of their length.

The nuclear apparatus is situated in the thin, anterior, hollowed part of the body. It is at first dumb-bell shaped, the “handle” of the dumb-bell being formed by a very slight connecting strand, which eventually separates, so that the flagellate becomes binucleate, and thus completes the general bisymmetry of the organism.

There is a karyosome in each nucleus. Other bodies of unknown function, and possibly composed of chromatin, occur on or near the axostyles.

Division has not been observed in the flagellate stages of the Lamblia, but it occurs within the cysts. The resistant cysts (fig. 20, e) are oval and are surrounded by a fairly thick, hyaline cyst wall. They measure 10 µ to 15 µ by 7 µ to 9 µ, and may be tetranucleate. According to Schaudinn, the cysts arise from the conjugation of two individuals, and nuclear rearrangement occurs.

L. intestinalis occurs in its flagellate stage in the duodenum and jejunum, and rarely as such in the other parts of the intestine. Normally it is found in the large intestine as cysts, which are voided with the fæces. The hosts of Lamblia include Mus musculus, M. rattus, M. decumanus, M. silvestris, Arvicola arvensis and A. amphibius, the dog and cat, rabbit, sheep and man. Cysts voided with the fæces of infected animals reach plants or drinking water, and thence are transferred to man.

The flagellate in these different hosts exhibits some variation in size and in the problematic chromatic bodies. Bensen has suggested the species L. intestinalis from man, L. muris from the mouse and L. cuniculi from the rabbit. It is not certain whether these different species are necessary, as the variation may be due to differences of environment.

Like Trichomonas, Lamblia can multiply under inflammatory conditions of the alimentary tract. Thus they are found in cases of diarrhœa, carcinoma of the stomach, etc. The parasites attach themselves by their sucking discs to the epithelial cells of the gut (fig. 20, c), and though their numbers may be very great, their direct pathological significance is not fully known. Their occurrence in cases of diarrhœa has been explained as being due to the increased peristalsis, which has detached the parasites from the epithelium. Free flagellate forms perish in stools if kept, more especially if the temperature falls below 0° C. or rises above 40° C. Lamblia has often been found in dysenteric diseases, especially in the East, and is said to be the causal agent of certain diarrhœas in India. Mathis (1914)[45] found Lamblia in cases of diarrhœa with dysenteriform stools in Tonkin. He also discovered healthy carriers of Lamblia cysts.

[45] Bull. Soc. Med. Chirurg. Indo-Chine, v, p. 55.

The parasite under discussion was first observed by Lambl (1859) in the mucous evacuations of children. He regarded the parasite as a Cercomonad and termed it Cercomonas intestinalis, which name as a rule is applied to Cercomonas hominis, Davaine, although Stein had already pointed out the difference between the two species. Grassi (1879) observed this species first in mice (calling it Dimorphus muris), and subsequently in human beings in Upper Italy and named it Megastoma entericum. Bütschli and Blanchard then laid stress on the identity of this species with Lambl’s C. intestinalis (1859), and consequently called it Megastoma intestinale. Later, Blanchard drew attention to the circumstance that the generic name Megastoma chosen by Grassi had already been used four times for various kinds of animals, and established the genus Lamblia. Accordingly, L. intestinalis is the valid name, and should be generally adopted.

In Upper Italy the parasite in the encysted condition has also been seen by Perroncito in man. At the same time, Grassi and Schewiakoff began a new investigation of specimens from mice and rats. In Germany, L. intestinalis was found by Moritz and Hölzl, Roos, Schuberg and Salomon. Moritz and Hölzl confirmed the relative frequency of the species. In Königsberg, Prussia, a student found encysted Lamblia in his fæces. One case was reported from Finland by Sievers, another case from Scandinavia by Müller. Frshezjesski and Ucke reported cases from Russia. Jaksch announced the occurrence of the parasite in Austria; Piccardi mentioned their presence again in Italy. They were reported from Egypt by Kruse and Pasquale, and from North America (Baltimore) by Stiles. Noc stated that 50 per cent. of the population of Tonkin harboured Lamblia. Finally, the structure of L. intestinalis has been described by Metzner (1901), and by Wenyon[46] (1907) in mice.

[46] Arch. f. Protistenkunde, Suppl. i, p. 169.

In all these cases L. intestinalis has been observed in the small intestine, or in the evacuations of patients with intestinal diseases. It has also been found in the intestine of healthy subjects. Just as Trichomonas intestinalis may be found inhabiting the stomach in diseases of that organ, in which an alkaline reaction is present (carcinoma), so has L. intestinalis been found to occur under similar circumstances (Cohnheim, Zabel). However, in Schmidt’s case, 1 per cent. hydrochloric acid was certainly stated to be present. Infection takes place by the ingestion of cysts (fig. 20, e), as was established by Grassi, experimentally on himself. Cereal food-stuffs, contaminated with Lamblia cysts from vermin of the locality, such as rats and mice, serve to convey the infection to man. Such cysts may probably be found in street-dust, etc. Stiles induced infection in guinea-pigs, and Perroncito in mice and rabbits, by means of cysts of Lamblia from human beings. Stiles suspected that flies could transport Lamblia cysts. Mathis (1914) found that L. intestinalis was not amenable to emetine, at any rate in its cystic stage.

Order. *Protomonadina*, Blochmann.

The smallness of the Protomonadines and their less superficial situation than the Polymastigines, may be the cause that so far as the species occurring in man are concerned, they were formerly less well known. As regards parasitic species, this group may be divided as follows, according to the number of flagella and the presence or absence of an undulating membrane:--

(1) Cercomonadidæ, with one flagellum at the anterior extremity, without an undulating membrane.

(2) Bodonidæ, with two flagella, without an undulating membrane, except in Trypanoplasma.

(3) Trypanosomidæ, with one flagellum, and an undulating membrane along the length of the body in some genera.

Family. *Cercomonadidæ*, Kent emend. Bütschli.

Small uniflagellate forms, without cytostome.

Genus. *Cercomonas*, Dujardin emend. Bütschli.

Oval or rounded organisms, with the aflagellar end often drawn out into a tail-like process.

*Cercomonas hominis*, Davaine, 1854.

Davaine found flagellates in the dejecta of cholera patients. They had pear-shaped bodies, lengthening to a point posteriorly. Their length was from 10 µ to 12 µ, and a flagellum about twice as long as the body projected from one extremity (fig. 21). A nucleus was hardly recognizable. Occasionally a somewhat long structure (cytostome?) appeared at the anterior extremity. The animals moved with remarkable activity. They also attached themselves by means of their posterior extremities and swung about around the point of attachment. Davaine found a smaller variety, only about 8 µ long, in the dejecta of a typhoid patient (fig. 21, b).

The Flagellata observed by Ekeckrantz (1869) in the intestine of man belong to this form--at least to the larger variety--and Tham (1870) reported fresh cases soon after. Lambl’s publication of 1875, which was written in Russian, and became known through Leuckart’s work on parasites, also alludes to apparently typical Cercomonads, which, however, were discovered, not in the intestine, but in an Echinococcus cyst in the liver (fig. 22). The elliptical, fusiform, rarely pear-shaped or cylindrical bodies of the parasites measured 5 µ to 14 µ in length, and were provided with a flagellum at one end, while the other extremity usually terminated in a long point. An oral aperture occurred at the base of the flagellum, and there were one or two vacuoles near the posterior extremity. Longitudinal division was also observed (fig. 22).

As already mentioned, this form, which Lambl termed Cercomonas intestinalis, differs considerably from the form found by the same author in 1859, which received the same designation (cf. Lamblia intestinalis, p. 60), but it corresponds with Cercomonas hominis, Davaine. The latter, as well as C. intestinalis, Lambl, 1875, is usually classed with the Trichomonads, but, as has already been remarked (cf. Trichomonas intestinalis, p. 54), this cannot be considered correct, as only one flagellum is present.

Cercomonas vaginalis (Castellani and Chalmers, 1909) was found in the vagina of native women in Ceylon.

Other species of Cercomonas have, at various times, been recorded from man. However, the parasitic species of the genus Cercomonas require further investigation.

According to Janowski (1896–7), typical Cercomonads have also been observed in the intestine of man by Escherich, also by Cahen, Massiutin, Fenoglio, Councilman and Lafleur, Dock, Kruse and Pasquale, Zunker, Quincke and Roos, and others. However, it is an open question whether the Flagellata observed by Roos in one of his cases belonged to Davaine’s species, the size showing some deviation (14 µ to 16 µ). In his, as in many other cases, doubts have been raised as to whether the flagellates found in the stools had actually lived in the intestine, or had subsequently appeared in the fæces: for this a surprisingly short time only is necessary. Salomon also appears to have observed Cercomonads (Berl. klin. Wochenschr., 1899, No. 46).

As with T. intestinalis so with C. hominis, it appears that the parasite settles not only in the intestine but also in the air-passages. This is demonstrated by the statements of Kannenberg and Streng of the occurrence of Monads and Cercomonads in the sputum and putrid expectoration in gangrene of the lungs, which no doubt apply to C. hominis (cf. also Artault). Possibly also the Flagellata observed in the pleural exudation by Litten and Roos may be included here; this is the more probable in Roos’s case as the process ensued in the pleura after the breaking through of a vomica.

Perroncito and Piccardi have described encysted stages of Cercomonads.

*Monas pyophila*, R. Blanch., 1895.

R. Blanchard thus designates a Flagellate that Grimm found in the sputum, as well as in the pus of a pulmonary and hepatic abscess, in the case of a Japanese woman living in Sapporo. The parasites resemble large spermatozoa (fig. 23). The body, 30 µ to 60 µ, has the shape of a heart or a myrtle leaf, and is surrounded by a thick cuticle which is supposed to extend into the interior of the body, dividing it into three parts. A long appendix at the rounded pole is covered for the greater part of its length by the cuticle; the extremity, however, is free and resembles a flagellum. The parasites were very active, frequently changed their shape, and were able to retract the long appendix within the body, which then assumed a round form.

[This organism requires further investigation.]

Family. *Bodonidæ*, Bütschli.

Protomonadina which are either free-living or parasitic, with two dissimilar flagella, while the possession of an undulating membrane and of a kinetic nucleus or blepharoplast is variable.

There are three genera:--

1. Bodo, Stein, 1878, without a kinetic nucleus and undulating membrane.

2. Prowazekia, Hartmann and Chagas, 1910, with a kinetic nucleus and without an undulating membrane.

3. Trypanoplasma, Laveran and Mesnil, 1901, with a kinetic nucleus and undulating membrane.

Of these genera Prowazekia must be discussed. Bodo does not occur in man. Species of Trypanoplasma occur in the blood and in the gut of various fishes, in the seminal receptacle of certain snails, in the gut and genitalia of a flatworm (Dendrocœlum lacteum) and in the vagina of a leech. Closely allied to Trypanoplasma is the genus Trypanophis, parasitic in the cœlenteric cavity of Siphonophores.

Genus. *Prowazekia*, Hartmann and Chagas, 1910.

The genus was founded for a flagellate parasite, Prowazekia cruzi, discovered in a culture of human fæces in Brazil. Various other species have been referred thereto. The genus is separated from Bodo by the possession of a second nucleus, the so-called kinetonucleus or blepharoplast. It differs from Trypanoplasma in the absence of an undulating membrane. It is heteromastigote, that is, it possesses two dissimilar flagella, one anteriorly directed and the other lateral and trailing.

The principal species are:

*Prowazekia urinaria*, Hassall, 1859.

Syn.: Bodo urinarius, Hassall, 1859; Trichomonas irregularis, Salisbury, 1868; Cystomonas urinaria, Blanchard, 1885; Plagiomonas urinaria, Braun, 1895.

Hassall[47] in 1859 first found Bodo-like flagellates in human urine. He examined fifty samples of urine from patients suffering from albuminuria and from cholera. The reaction of the urine was alkaline or sometimes only feebly acid. The flagellates were only seen after the urine had been standing for several days. Hassall named the organism Bodo urinarius, and gave a very good description of it with illustrations. The flagellate, which was round or oval, measured 14 µ by 8 µ. The organism had “one, usually two, and sometimes three lashes or cilia.” In 1868 Salisbury described a similar flagellate in the urine under the name Trichomonas irregularis. Künstler in 1883 described the latter parasite under the name B. urinarius. In 1885 Blanchard, considering Künstler’s organism a different parasite from Hassall’s, called it Cystomonas urinaria. Braun, in 1895, gave the name Plagiomonas urinaria. Barrois (1894) considered Künstler’s and Hassall’s organisms to be identical and not to be true parasites of man. Sinton,[48] in 1912, found the flagellate in the deposit, after centrifuging, of a 24-hour old specimen of alkaline urine from a Mexican sailor in the Royal Southern Hospital, Liverpool. Sinton found a kinetic nucleus or blepharoplast in the organism, and therefore placed it in the genus Prowazekia.

[47] Lancet, 1859, ii, p. 503.

[48] Annals Trop. Med. and Parasitology, vi, p. 245.

The flagellate stage (fig. 24) of the organism is polymorphic, and may be either (a) sausage-shaped, 10 µ to 25 µ in length by 2·5 µ to 6 µ in breadth; (b) round or oval, varying from 4 µ in diameter to oval forms 15 µ by 10 µ; (c) a carrot-shaped form, of varying size up to 25 µ by 4 µ. The kinetic nucleus is large and pear-shaped. Near it are basal granules, closely applied to one another, from which the flagella arise. There is a small cytostome near the roots of the flagella. There is a well-marked karyosome in the nucleus. The movement is jerky. The shorter, anterior flagellum may be used in food-capture. In life, bacteria have been seen to be ingested. Food-vacuoles tend to accumulate at the posterior (aflagellar) end. A contractile vacuole may be present, near the base of the cytostome, and may really be the dilated fundus of the latter. Division occurs by binary fission. The organism can encyst (fig. 25, a), when the flagella are lost, and round or oval cysts are found, 5 µ to 7 µ in diameter. After a time flagella are formed inside the cyst, and the organism emerges therefrom in its typical flagellate form (fig. 25, b-f).

Sinton’s case is interesting. He obtained the flagellate only twice from the same patient, a Mexican then in hospital in Liverpool. The flagellate was not found in the patient’s fæces, nor was it found in the urine on later occasions when taken aseptically.

In cultures Prowazekia urinaria was always found in association with bacteria. The cultures died at a temperature of 37° C., but grew well at 20° C. Various media were useful at the lower temperature, such as urine, salt agar, nutrient agar, serum agar, blood agar, peptone salt solution, and diluted blood serum. The flagellate was, then, considered to be an accidental contamination and not a true parasite of human urine.

*Prowazekia asiatica*, Castellani and Chalmers, 1910.

The flagellate was found by the discoverers in the stools of patients suffering from ankylostomiasis and diarrhœa in Ceylon. It was referred by them to the genus Bodo, but in 1911 Whitmore[49] further studied it and placed it in the genus Prowazekia. In the stools the flagellate is found either as a long, slender form measuring 10 µ to 16 µ by 5 µ to 8 µ or as a rounded form 8 µ to 10 µ in diameter. Its cytoplasm is alveolar. A rhizoplast connects the basal granules to the kinetic nucleus. There is multiplication and cyst formation as before. The organism is easily cultivated, especially in the condensation water of nutrose agar and maltose agar. The pathogenicity is stated to be nil.

[49] Arch. f. Protistenk. xxii, p. 370.

*Prowazekia javanensis*, Flu, 1912.

Found in agar cultures from the motions of patients at Weltevreden, Dutch East Indies.[50] The flagellates are 12 µ long and 5 µ broad. The lateral flagellum is stated to be attached to the cell body for a short distance. Regarding the karyosome in the nucleus, the author states that the smaller the karyosome the more chromatin is deposited on the nuclear membrane. Flu mentions that the specific name javanensis is a temporary one, as in the course of time it may be shown that there is only one species of Prowazekia.

[50] Geneesk. Tijdschr. v. Nederl. Ind., lii, p. 659; _Med. v. d. Burg. Geneesk. d. Nederl. Ind._, iii, p. 1.

*Prowazekia cruzi*, Hartmann and Chagas, 1910.

Found in a culture from human fæces on an agar plate in Brazil, and considered to be a free-living form.[51] The organism is oval or pear-shaped, 8 µ to 12 µ long and 5 µ to 6 µ broad. In human stools at Tsingtau, China, a Prowazekia has been found by Martini which he thinks is the same as Prowazekia cruzi. He considers it to be a cause of human diarrhœa and intestinal catarrh.

[51] Mem. Inst. Osw. Cruz., ii, p. 64.

*Prowazekia weinbergi*, Mathis and Léger, 1910.

This species was found in the fæces of men, both healthy and diarrhœic, in Tonkin.[52] It is pear-shaped, 8 µ to 15 µ long by 4 µ to 6·5 µ broad. The flagella occur at the broad end.

[52] Bull. Soc. Med. Chir. Indo-Chine, i, p. 471.

The discoverers think that Prowazekia weinbergi is an intestinal inhabitant, but non-pathogenic, since it was found to occur in the fæces even when obtained with aseptic precautions.

*Prowazekia parva*, Nägler, 1910.

A free-living form found in the slime on the stones at the biological station at Lunz. Another Prowazekia was found in 1914 in tap-water in Calcutta.

Family. *Trypanosomidæ*, Doflein.

The Trypanosomidæ, broadly considered, are uniflagellate organisms, the flagellum being at the anterior end. The flagellum arises near the blepharoplast (kinetic nucleus), which lies anterior, near or posterior to the nucleus.

The following genera will be considered:--

Trypanosoma--with an undulating membrane along the length of the body.

Crithidia--with a less well-developed undulating membrane anteriorly (see fig. 49).

Herpetomonas--including the so-called Leptomonas, with anterior free flagellum only, and no undulating membrane.

Leishmania--non-flagellate forms in mammalian blood, flagellate herpetomonad stages in culture, probably occurring naturally in Arthropods.

Genus. *Trypanosoma*, Gruby, 1843.

The members of the genus possess a single flagellum, which arises posteriorly, adjacent to a blepharoplast or kinetic nucleus. The flagellum forms a margin to an undulating membrane, and may or may not be continued beyond the body as a free flagellum. Many species are parasitic in vertebrate blood and in the digestive tracts of insects.

HISTORICAL.

The history of blood flagellates goes back to the year 1841, in which Valentin discovered in the blood of a brook-trout (Salmo fario L.) minute bodies, from 7 µ to 13 µ in length, with active movements and presenting marked changes in form. Valentin considered the parasite a new species of the old genus Proteus or Amœba, Ehrbg. This announcement led Gluge (1842) to publish a similar discovery he had made in frog’s blood. The latter forms were called by Mayer (1843) Amœba rotatoria, Paramœcium loricatum and P. costatum, while Gruby (1843) called them Trypanosoma sanguinis.[53] Later it was discovered that similar organisms occurred also in the blood of birds (Wedl (1850), Danilewsky) and of mammals. Gros (1845) found them in the mouse and mole, Chaussat (1850) in the house rat, Lewis (1879) in the Indian rat, Wittich (1881) in the hamster. Danilewsky (1886–89) and Chalachnikow (1888) investigated the structure and division of trypanosomes.

[53] Gruby’s generic name is generally accepted. Still others have been used, e.g., Undulina, Ray Lankester, Globularia Wedl, Paramecioides Grassi, Trypanomonas Danilewsky, Hæmatomonas Mitrophanow.

In the case of all these forms, there was no discussion as to a pathogenic influence on the host. Opinion, however, as to the action of trypanosomes changed when, in 1880, Evans found flagellates in the blood of horses in India that suffered from a disease endemic there called “surra,” and associated the parasites with the disease. Steel and Evans were successful in transmitting the parasites--first known as Spirochæta evansi, Steel, then as Trichomonas evansi, Crookshank, and finally as Trypanosoma evansi--to dogs, mules and horses. They recognized that the above mentioned flagellates in the blood of the experimental animals were the causal agents of the disease.

From that time there was a considerable increase in the literature, the contents of which have been summarized by Laveran and Blanchard. In 1894 Rouget discovered trypanosomes in the blood of African horses that suffer from “stallion’s disease” (dourine). In 1894 Bruce found similar forms (T. brucei) in the blood of South African mammals suffering from “nagana,” and in consequence attention was drawn to the part which the much dreaded tsetse-fly played in the transmission of “nagana.” In 1901 Elmassian discovered trypanosomes in the blood of horses that were stricken with “mal de caderas,” which is very common in the Argentine. The disease in cattle named “galziekte” (gall-sickness), occurring in the Transvaal, was also at one time attributed to a trypanosome remarkable for its great size, and like some other species, bearing the name of its discoverer (T. theileri).

The study of the species hitherto known has been carried on partly by the above mentioned authors and in part by others, e.g., Rabinowitsch and Kempner, Laveran and Mesnil, Wasiliewski, Senn. It was greatly advanced by the method of double staining (with alkaline methylene blue and eosin) introduced by Romanowsky (1891) and elaborated by Ziemann, Leishman, Giemsa and others. By this means the presence of a terminal flagellum and of an undulating membrane at the side of the flattened and extended body was demonstrated. Laveran and Mesnil (1901) discovered allied flagellates in the blood of the fish, Scardinius erythrophthalmus. These flagellates, now placed in the genus Trypanoplasma, had a second free flagellum in addition to the one bordering the undulating membrane. Trypanoplasms have since been found in both freshwater and marine fishes. The transmission of trypanoplasms of freshwater fishes is effected by leeches. Trypanoplasma varium from Cobitis is transmitted by Hemiclepsis marginata according to Léger, while the Trypanoplasmata of Cyprinus carpio and Abramis brama reach new hosts by the agency of Piscicola according to Keysselitz.

Another ally of the Trypanosomidæ, Trypanophis, lives in the cœlenteric cavity of Siphonophores. It has also an extra terminal flagellum (Poche, Keysselitz). [Trypanoplasma and Trypanophis belong to the Bodonidæ, see p. 63].

Finally it was shown that Trypanosomes occurred in human beings. Although Nepveu’s early report of trypanosomes in the blood of malarial patients may be doubtful, subsequent researches by Forde and Dutton demonstrated trypanosomes (fig. 28) in the blood of a European, apparently suffering from malaria, living in the Gambia. Dutton (1902) called the human trypanosome, T. gambiense. The expedition despatched by the Liverpool School of Tropical Medicine (1902) to Senegambia found trypanosome infections in six cases among a thousand inhabitants examined.

About the same time attention was devoted to the disease of West African negroes known for a century as “sleeping sickness.” Castellani (1903) was the first to succeed in demonstrating the presence of trypanosomes (at first called T. ugandense) in centrifugalized cerebro-spinal fluid obtained by puncture from cases of sleeping sickness in Uganda. Similar discoveries were made by Bruce, who also found trypanosomes in the blood of those attacked with sleeping sickness. Sambon regarded a species of Glossina as the transmitter. From consideration of the geographical distribution of the disease Christy regarded Glossina palpalis as the transmitter. Brumpt first thought it was G. morsitans, but, later, supported the view of G. palpalis. Bruce, Nabarro and Greig also named the same insect as the transmitter, not only for geographical reasons but also because healthy apes became infected by the bite of certain G. palpalis. The inoculation of cerebro-spinal fluid from subjects of sleeping sickness into the spinal canal of apes (Macacus) had the same result.

Just as the discovery of the malarial parasites called forth a whole flood of research memoirs which were followed by a second series on the relation of the mosquitoes to malaria, so a similar outpouring occurred after the discovery of the pathogenic trypanosomes of mammals and men. In both cases the inquiry was not limited to the stages in man and other vertebrate hosts, but the fate of the parasites in the intermediate (invertebrate) hosts was investigated, and allied species were obtained from many different hosts.

Novy and MacNeal (1903) were the first to cultivate trypanosomes in artificial media (blood-agar).

In 1910 Stephens and Fantham recorded the presence of another human trypanosome, T. rhodesiense, from a case of sleeping sickness in Rhodesia, where G. palpalis was absent. Kinghorn has since demonstrated that T. rhodesiense is transmitted by G. morsitans. Kinghorn and Yorke believe that big game (e.g., antelope) is the reservoir of T. rhodesiense.

The output of literature on trypanosomiasis in men and animals is enormous. To cope with it the Sleeping Sickness Bureau Bulletin was founded in 1908, and it is now (since November 1912) continued as a section of the Tropical Diseases Bulletin, wherein current literature is reviewed.

GENERAL.

Trypanosomes occur in the blood of representatives of all the vertebrate classes. Often the trypanosomes occur so scantily in the blood that they are overlooked on examination. A useful aid in detecting the flagellates in such cases consists in the use of cultures of the blood of the host on artificial media. Stimulated by the medium multiplication occurs, and hence the parasites are more easily detected. [For the composition of such culture media see Appendix.]

There is a periodicity in the appearance of the trypanosomes in the peripheral blood of the host, due to alternating phases of multiplication and of rest on the part of the parasites. Such periodicity has been established both by biological and enumerative methods. Again, a seasonal variation has been observed in the occurrence of certain trypanosomes in the peripheral circulation of the hosts; for example, some trypanosomes (e.g., T. noctuæ in birds) are found only in the summer in the blood, while in the winter they occur in the internal organs.

Recent cultural researches have established that trypanosomes, e.g., T. americanum, may be present in very small numbers in hosts, such as cattle, which are quite unharmed by them, and in which the presence of these flagellates formerly was never suspected (“cryptic trypanosomiasis.”) However, the majority of the trypanosomes occurring in domestic animals are usually deleterious or even lethal to their hosts. Many wild animals, such as various species of antelope, harbour trypanosomes without being injured thereby. In such cases it is probable that the vertebrate hosts have been so long parasitized in the past, that they have become tolerant and immune to the effects of the flagellates. Should such trypanosomes of wild animals be transmitted to domesticated stock or man, they may re-acquire their initial virulence and become pathogenic to the new host. As a general statement, the newer a parasite is to its host the greater is its virulence. For example, T. gambiense, T. rhodesiense and T. brucei are innocuous to big game in Africa, but are pathogenic to man and domestic animals respectively. Pathogenic trypanosomes appear to have a wider range of hosts, that is, to be less limited to one specific host than non-pathogenic forms. Thus, T. rhodesiense is pathogenic to man and all laboratory animals, while it is non-pathogenic to antelopes and their kind.

Morphology.

The general structure of the various trypanosomes shows much uniformity, though variations in size and shape occur. Typically the body is elongate and sinuous. The flagellar end tapers gradually to a point, the aflagellar extremity usually being rounded or more blunt. In some trypanosomes there is much diversity in size, the organisms varying from long, slender forms to short, stumpy ones; in other species relative constancy of size is maintained. The former are known as polymorphic trypanosomes, the latter as monomorphic forms.

Two nuclei are present. The main or principal nucleus, sometimes termed the trophic nucleus, is often situated towards the centre of the body; it is frequently of the vesicular type, containing a karyosome. The blepharoplast or kinetic nucleus is posterior to the nucleus, and usually is rod-like. The flagellum arises close to the blepharoplast, and forms an edge to the undulating membrane. It may or may not extend beyond the limits of the undulating membrane. If it does so, the unattached part is known as the free flagellum. Sometimes a small granule is found at the origin of the flagellum. This is the basal granule, and is considered by some to function as the centriole of the kinetic nucleus.

The undulating membrane is a lateral extension of the ectoplasm or periplast, and is the main agent in locomotion. It is edged by the flagellum, which forms a deeply stainable border to it. Within the membrane substance, often arranged parallel with its edge, are a number of fine contractile elements, the myonemes. These contractile elements may also occur on the body of the trypanosome. They are easily seen in some large trypanosomes, but are difficult of demonstration in others, owing to their great fineness.

Multiplication of trypanosomes in the blood is brought about by binary longitudinal fission (fig. 26). Division is initiated by that of the blepharoplast and nucleus. The division may be equal or subequal, whereby differences in size of individuals partly arise. Multiple division by repeated binary fission, without complete separation of the daughter forms, is known in some trypanosomes (e.g., T. lewisi), and rosettes of parasites thereby are produced (fig. 27).

The classification of trypanosomes is very difficult. Laveran (1911)[54] has suggested the examination of the relative length of the flagellum as a diagnostic character, and so arranged these flagellates in mammals in three groups. The first group included those trypanosomes always having part of the flagellum free (e.g., T. evansi, T. vivax); the second group comprised forms without a part of the flagellum free (e.g., T. congolense), while the third group included forms some members of which have free flagella, while others have not (e.g., T. gambiense). Bruce[55] (1914) and Yorke and Blacklock[56] (1914) have also devised classifications.

[54] Ann. Inst. Pasteur, xxv, p. 497.

[55] Trans. Soc. Trop. Med. & Hyg., viii, p. 1.

[56] Annals Trop. Med. and Parasitol., viii, p. 1.

Resting stages of some trypanosomes have been found in the internal organs of their vertebrate hosts. The formation of these oval, Leishmania-like bodies will be noted in individual cases later. Similar small oval bodies form an important phase in the life-history of T. cruzi, which multiplies normally by multiple fission or schizogony into these oval, daughter elements, and not by binary longitudinal fission in the circulating blood.

Polymorphism in trypanosomes (e.g., T. gambiense, T. rhodesiense) is now interpreted as a phenomenon resulting from growth and division.[57] Long, thin forms are those about to divide. Fully mature forms are shorter and broader. Various intermediate types occur and represent growth forms. Formerly, polymorphism was interpreted in terms of sex, thin forms being regarded as males, broad forms as females, while the intermediate types were termed indifferent. Conjugation was not observed, and there is no evidence in support of the sexual interpretation.

[57] Robertson (1912), Proc. Roy. Soc., B, lxxxv, p. 527.

The transmission of trypanosomes from one vertebrate host to another is usually accomplished by the intermediation of some biting arthropod in the case of terrestrial animals, while leeches are usually considered to act as transmitters in the case of the trypanosomes occurring in aquatic animals. Developmental phases of the life-histories of trypanosomes occur in the invertebrate transmitters, and will be considered in individual cases.

*Trypanosoma gambiense*, Dutton, 1902.

Syn.: Trypanosoma hominis, Manson, 1903. Trypanosoma nepveui, Sambon, 1903. Trypanosoma castellanii, Kruse, 1903. Trypanosoma ugandense, Castellani, 1903. Trypanosoma fordii, Maxwell Adams.

In vertebrate blood Trypanosoma gambiense is polymorphic, for long, thin forms may be seen in contrast with short, stumpy forms, as well as intermediate forms (fig. 29, a--c). This polymorphism has been interpreted in terms of sex, especially by German investigators, following Schaudinn (see above). However, there is no evidence of conjugation, and the polymorphic forms are more easily interpreted in terms of growth and division, for the long thin forms are potential dividing organisms, and the stumpy or short parasites, with little or no free flagellum, are the adult individuals.

Morphology of T. gambiense in the Circulating Blood.

T. gambiense varies from 13 µ to 36 µ in length, its average length being 24·8 µ, as was determined in 1913 by exact biometrical methods by Stephens and Fantham.[58] Three forms of parasite occur. According to Miss Robertson,[59] the relatively short forms from 13 µ to 21 µ long may be regarded as the mature or “adult” type of parasite in the blood. They carry on the cycle in the vertebrate. From them intermediate forms, which are longer than the “adult” but at first have the same breadth, arise by growth. They possess a free flagellum. The intermediate forms grow into long individuals, which are those about to divide. The products of division give rise, directly or indirectly, to the adult forms.

[58] Annals Trop. Med. and Parasitol., vii, p. 27.

[59] Phil. Trans., B (1913), cciii, pp. 161–184.

The organism has an elongate body with an anterior or flagellar end and a blunter posterior or non-flagellar end. The protoplasm is finely granular, large inclusions being rare. The central nucleus is oval and large, often containing most of its chromatin concentrated as a karyosome, with small granules only scattered near or on the fine nuclear membrane. The blepharoplast is either rounded or rod-shaped. The undulating membrane is thrown into folds and is bordered by the flagellum. A small basal granule may be present near, or at the actual origin of the flagellum.

Multiplication in the vertebrate is brought about by longitudinal division. According to the recent account of division by Miss Robertson, the blepharoplast doubles, then the flagellum splits for the greater part of its length, and the daughter flagella separate, one being shorter than the parent flagellum. The nucleus often shows two well marked dark granules on the membrane at opposite poles, and these appear to act as centrosomes. Nuclear constriction occurs and the halves gradually separate. Finally the two daughter organisms become free, the aflagellar end splitting last. The products of division may be equal or unequal. Repeated division goes on in the general circulation until the blood swarms with parasites. Then the trypanosomes gradually disappear, and a period occurs when it is practically impossible to demonstrate the parasite in the blood. At such a period, trypanosomes can be obtained by puncture of the enlarged lymphatic glands or of the spinal canal, or can be found in the internal organs, more particularly in the spleen, lungs, liver and bone-marrow. In the latter organs, latent bodies are produced (fig. 29, d--f) which are capable of again becoming flagellates and entering the general circulation. Their formation was described by Fantham (1911).[60] The parasite contracts, the blepharoplast migrates towards the nucleus, a very thin coat differentiates around the two nuclei and a certain amount of cytoplasm, and the parts exterior to the coat disintegrate, leaving a small, oval body behind. Fuller details are given in connection with T. rhodesiense. Laveran (1911)[61] considers that latent bodies are “involution” forms, but acknowledges that they can flagellate and become infective in fresh blood.

[60] Proc. Roy. Soc., B, lxxxiii, p. 212.

[61] C. R. Acad. Sci., 153, p. 649.

No multiplication of the trypanosomes within the cells of the lung, liver or spleen of infected monkeys was found by Miss Robertson in her recent researches.

There appear to be negative periods in infected monkeys, since, although trypanosomes may occur in their blood at such times, they are not infective to Glossina.

Development in Glossina palpalis.--The principal accounts are those by Sir D. Bruce and his colleagues (1911),[62] and by Miss Robertson[63] (1912), whose results will be followed. According to the latter investigator T. gambiense never enters the body cells of the fly (G. palpalis), nor does it penetrate the gut wall into the body cavity. Practically no crithidial stage occurs in the fly’s main gut, but a trypanosome facies is retained therein.

[62] Proc. Roy. Soc., B, lxxxiii, p. 513.

[63] Proc. Roy. Soc., B, lxxxvi, p. 66.

After the trypanosomes are ingested by the fly during a meal of infected blood, sooner or later multiplication occurs. This development usually begins in the middle or posterior part of the mid gut, and trypanosomes of varying sizes are produced. After the tenth or twelfth day, many long, slender trypanosomes (fig. 30, a) are found, which gradually move forwards into the proventriculus. Such long, slender forms represent the limit of development in the lumen of the main gut. The proventricular type, developed about the eighth to the eighteenth or twentieth day, is not infective; it may occur in the crop, but is not to be found permanently there. Between the tenth and the fifteenth days multinucleate forms of trypanosomes are found, and may be styled multiple forms (fig. 30, b). Some of these latter may be degenerative.

Invasion of the Salivary Glands of the Fly.--Long, slender trypanosomes from the proventriculus pass forward into the hypopharynx. They then pass back along the salivary ducts, about sixteen to thirty days after the fly’s feed. The trypanosomes reach the salivary glands as long, slender forms. In the glands they become shorter and broader, attach themselves to the surrounding structures, and assume the crithidial facies (fig. 30, c, d). As crithidial forms they remain attached to the wall and multiply in the glands. These crithidial stages differentiate into the short, broad trypanosome forms, capable of swimming freely (fig. 30, e).

Miss Robertson considers the development in the main gut to be indifferent multiplication, and that salivary fluid seems necessary to stimulate trypanosomes to the apparently essential reversion to the crithidial type. The second development in the salivary gland is the essential feature. The short, stumpy forms of trypanosomes (fig. 30, e) finally produced in the salivary glands are alone infective. No conjugation of trypanosomes occurs in the fly. Only about 5 per cent. of captive tsetse flies fed on trypanosome-infected blood become infective, but they probably remain infective for the rest of their lives.

J. G. Thomson and Sinton (1912)[64] have obtained in cultures the various trypanosome forms of T. gambiense seen in the fly’s main gut.

[64] Annals Trop. Med. and Parasitol., vi, p. 331.

Duke (1912)[65] found T. gambiense in a species of antelope, the situtunga (Tragelaphus spekei), on Damba Island in Victoria Nyanza. Wild G. palpalis could be infected therefrom. The antelope may then act as a sleeping sickness reservoir in that district, but men are apparently the chief reservoir.

[65] Proc. Roy. Soc., B, lxxxv, pp. 156, 483.

*Trypanosoma nigeriense*, Macfie, 1913.[66]

Macfie has recently (August, 1913) described a human trypanosome from the Eket district of Southern Nigeria. It is common in young people. The disease produced does not seem to be of a virulent type in Nigeria, and does not occur in epidemic form. In the early stages the glands of the neck are enlarged. In the later stages--cases of which are rarer--lethargy appears. The parasite is a polymorphic trypanosome, morphologically almost indistinguishable from T. gambiense, though it may be slightly shorter. Macfie recorded the occurrence in his preparations of a few trypanosomes appearing to have a flagellum free during their whole length. Some of the parasites, as seen in a sub-inoculated guinea-pig, are very small (8 µ long). Other trypanosomes have their nuclei displaced somewhat anteriorly. This parasite may only be a variety of T. gambiense. The parasite is perhaps spread by Glossina tachinoides.

[66] Annals Trop. Med. and Parasitol., vii, p. 339; viii, p. 379.

*Trypanosoma rhodesiense*, Stephens and Fantham, 1910.

The parasite was found in the blood of a young Englishman who had contracted sleeping sickness in the Luangwa Valley, North-eastern Rhodesia, in the autumn of 1909. The patient had never been in an area infested with Glossina palpalis.

(1) Morphology.--The morphology of the parasite in man and sub-inoculated rats was studied by Stephens and Fantham in 1910.[67] They pointed out a morphological peculiarity in the presence of certain trypanosomes with posterior nuclei in sub-inoculated animals, that is, parasites in which the nucleus (trophonucleus) was situated towards the posterior or aflagellar end, close up to or even beyond the blepharoplast or kinetic nucleus (fig. 31, 4, 5). When the nucleus was beside the blepharoplast, the former was seen to be kidney-shaped (fig. 31, 4). The posterior nuclear forms were of the stout and stumpy variety, and about 6 per cent. of the stumpy forms were found to have their nuclei displaced from the centre. The anterior or flagellar end of these trypanosomes often contained chromatoid granules. T. rhodesiense varies in length from 12 µ to 39 µ[68]; short stumpy forms vary from 13 µ to 21 µ, intermediate forms from 21 µ to 24 µ, and long, slender forms from 25 µ onwards. The average length is 24·1 µ.

[67] Proc. Roy. Soc., B, lxxxiii, p. 28.

[68] Stephens and Fantham (1912–13), Proc. Roy. Soc., B, lxxxv, p. 223, and Annals Trop. Med. and Parasitol., vii, p. 27.

Certain regular periods occur in the course of the trypanosomiasis when few or no flagellate trypanosomes are found in the peripheral blood of the patient or of the sub-inoculated animal. These periods can be explained in terms of morphology, for the trypanosomes are capable of assuming a non-flagellate form in the internal organs of the host, particularly in the lungs and in the spleen. Such forms are known as “latent” or “resting” forms. The term “latent body” was first used by Moore and Breinl in 1907[69] in connection with T. gambiense. Fantham[70] (1911) has described the process of formation of latent from motile forms and the reconversion of the latent bodies into active flagellates. Fresh preparations of splenic blood or lung blood containing trypanosomes were made. A trypanosome gradually withdrew or cast off its flagellum, concentrated its cytoplasm, and became more or less elongate oval. Nucleus and blepharoplast approached one another and came to lie more or less side by side. Then an opaque line often made its appearance around the nuclear area and differentiated as a slight envelope or covering, the cytoplasm external to this merely degenerating. The small, oval, refractile body (fig. 29, d--f) thus formed was a non-flagellate latent body, 2 µ to 4 µ in diameter, like Leishmania or the non-flagellate, multiplicative forms of T. cruzi (fig. 34), and remains temporarily inactive in the internal organs of the host. After this period of inactivity, the non-flagellate body, recuperated by its rest, begins to elongate again. The nuclei separate. From a small vacuole-like portion the flagellum differentiates and forces out the ectoplasm, which assumes the form of the undulating membrane with its flagellar border. Subsequent growth results in the production of the typical trypanosome form, which re-enters the circulating blood and multiplies by longitudinal binary fission. Division of the parasite prior to the formation of a latent body may occur and division of the latent forms themselves is known, though less common. Consequently latent bodies, like the flagellate forms themselves, show diversity in size. The blepharoplast of the latent bodies is sometimes less well marked than in Leishmania (see fig. 29, d-f). Laveran’s views on these bodies have already been given on p. 74.

[69] Annals Trop. Med. and Parasitol., i, p. 441.

[70] Proc. Roy. Soc., B, lxxxiii, p. 212.

(2) Animal Reactions.--The posterior nuclear trypanosomes were found in all sub-inoculated animals, such as rats, guinea-pigs, dogs, mice, Macacus, rabbits and horses, but were not seen in the human patient, as few trypanosomes occurred in his peripheral blood. R. Ross and D. Thomson[71] found a periodic, cyclical variation in the number of the parasites in the patient’s blood from day to day, the cyclical period being about a week (fig. 32). Fantham and J. G. Thomson[72] (1911) found a similar periodic, cyclical variation in the trypanosomes in the blood of sub-inoculated rats, guinea-pigs and rabbits. On counting the parasites in the blood of similar animals inoculated with T. gambiense, they established, by enumerative methods, that T. rhodesiense was more virulent than T. gambiense, while Yorke also showed this marked virulence of T. rhodesiense in practically all laboratory animals. In other words the duration of infection in the case of T. rhodesiense was shorter. It was also found that T. rhodesiense was resistant to atoxyl. The patient, from whom the original strain was obtained, died about nine months after the probable date of infection. Some patients infected with T. rhodesiense have died in an even shorter period, such as four or five months.

[71] Proc. Roy. Soc., B, lxxxii, p. 411.

[72] Annals Trop. Med. and Parasitol., iv, p. 417.

In sheep and goats T. rhodesiense causes an acute disease, marked by high fever, œdema of the face, and keratitis, as shown by Bevan and others, death resulting after a relatively short period. T. gambiense gives rise, in these animals, to no symptoms except fever, which may be overlooked. T. rhodesiense produces keratitis in dogs.

Stannus and Yorke (1911) observed T. rhodesiense in animals inoculated from a case of sleeping sickness in Nyasaland. Sir D. Bruce and his colleagues[73] have shown (1912) that T. rhodesiense is the parasite usually found in man and in animals sub-inoculated from cases of sleeping sickness in Nyasaland. It has since been found in German East Africa and Portuguese East Africa, while Ellacombe has described a case from North-western Rhodesia.

[73] Proc. Roy. Soc., B, lxxxv, p. 423.

(3) Serum Reactions.--Interesting experiments on this subject were performed during 1911 and 1912 by various French investigators.

(a) Action of Immune Serum (Mesnil and Ringenbach)[74]: (1) A goat was infected with T. rhodesiense. Twenty-two days later its serum mixed with T. rhodesiense was injected into a mouse. Result: Protection. (2) The serum mixed with T. gambiense was injected into a mouse. Result: Infection.

[74] C.R. Soc. Biol., lxxii, p. 58.

(b) Action of Baboon Serum.--Contrary to T. gambiense, T. rhodesiense is very susceptible to human and baboon sera. Mesnil and Ringenbach[75] showed that a dose of 1 c.c. of baboon (Papio anubis) serum cured mice infected with T. rhodesiense. In the same dose it acted very feebly on T. gambiense.

[75] C.R. Acad. Sci., 153, p. 1,097.

(c) Action of Human Serum.--1 c.c. of human serum cured T. rhodesiense mice in three out of four cases; on T. gambiense mice there was no appreciable effect.

Laveran and Nattan-Larrier[76] have shown the same, namely, that human sera act on T. rhodesiense, but are quite without action on T. gambiense.

[76] C.R. Acad. Sci., 154, p. 18.

(d) Trypanolytic Reactions.--Mesnil and Ringenbach[77] have also shown that the sera of animals (man, monkey and guinea-pig) infected with T. gambiense are trypanolytic for the homologous trypanosome, that is, T. gambiense, but have no action on the heterologous trypanosome, that is, T. rhodesiense.

[77] C.R. Soc. Biol., lxxi, p. 609.

(4) Cross Immunity Experiments.--(a) Mesnil and Ringenbach[78] immunized a monkey (Macacus rhesus) against T. gambiense. It was inoculated with T. rhodesiense on June 7, 1911; on June 27 trypanosomes appeared, the infection being slight; on July 4 it died. A control died in ten and a half days.

[78] C.R. Soc. Biol., lxxi, p. 271.

(b) Laveran[79] immunized a goat and mice against T. gambiense. When they had acquired a solid immunity, they were inoculated with T. rhodesiense. They became infected like the controls.

[79] Bull. Soc. Path. Exot., v, pp. 26, 241.

(c) Laveran and Nattan-Larrier[80] immunized a ram against T. brucei, it subsequently became infected with T. rhodesiense.

[80] C.R. Acad. Sci., 154, p. 18.

(d) Laveran[81] immunized a ram and a sheep against different strains of T_. brucei_. Inoculated with T. rhodesiense they both acquired acute infections and died. Conclusion: T. rhodesiense is not T. brucei.

[81] Bull. Soc. Path. Exot., v, p. 101.

When the converse set of experiments is tried, namely, immunizing an animal against T. rhodesiense, and then inoculating with T. gambiense, the difficulty immediately arises that it is impossible to immunize an animal against T. rhodesiense, owing to its virulence. But a partial and transitory immunity to T. rhodesiense can be obtained by treating the infected animal with drugs, such as arsenophenylglycin. The results, so far as they go, seem to show that an animal immunized against T. rhodesiense is immune not only to T. rhodesiense, but also to T. gambiense, a fact which, according to Mesnil and Léger, does not invalidate the specificity of T. rhodesiense, but tends to show that the two trypanosomes are closely related.

(5) Mode of Transmission and Reservoir.--Kinghorn has shown that T. rhodesiense is transmitted by Glossina morsitans in which it undergoes development. Kinghorn and Yorke[82] found that about 16 per cent. of the wild game examined in Northern Rhodesia was naturally infected with T. rhodesiense. The wild game examined included waterbuck, hartebeest, mpala, bushbuck and warthogs. One native dog near the Nyasaland border was found infected, but not domestic stock. Taute doubts whether T. rhodesiense really occurs in wild game. Approximately 3·5 per cent. of the tsetse flies fed on infected animals may become permanently infected with T. rhodesiense, and capable of infecting clean animals. Furthermore, a tsetse fly when once infective probably remains infective for the rest of its life.

[82] Annals Trop. Med. and Parasitol., vii, p. 183.

Kinghorn and Yorke, however, have shown that climatic conditions, namely, those of temperature, also affect the infectivity of the tsetse fly, as the ratio of flies capable of transmitting T. rhodesiense to those incapable of transmitting the virus is 1 : 534 in hot valley districts (e.g., Nawalia, Luangwa Valley, temperature 75° to 85° F.), while on elevated plateaux (e.g., Ngoa, on the Congo-Zambesi watershed, temperature 60° to 70° F.) the ratio falls to 1 : 1312.

Mechanical transmission by the tsetse fly does not occur, if a period of twenty-four hours has elapsed since the infecting meal.

Developmental Cycle in the Fly.--The period which elapses between the infecting feed of the flies and the date on which they become infective varies from eleven to twenty-five days in the Luangwa Valley, according to Kinghorn and Yorke. Attempts carried out at laboratory temperature on the Congo-Zambesi plateau, during the cold season, to transmit T. rhodesiense by means of G. morsitans were always unsuccessful. The developmental cycle of the trypanosome in the fly is influenced by the temperature to which the flies are subjected (as stated above). The first portion of the developmental cycle proceeds at the lower temperatures (60° to 70° F.), but higher temperatures are necessary for the completion of the development of the trypanosome. Kinghorn and Yorke found that the trypanosomes may persist in the fly, at an incomplete stage of their development, for at least sixty days when the climatic conditions were unfavourable.

The first portion of the developmental cycle of the trypanosome takes place in the gut of the fly. Invasion of the salivary glands of the tsetse is secondary to that of the intestine, but is necessary for the infectivity of the fly. A relatively high mean temperature, 75° to 85° F., is essential for the passage of the trypanosomes into the salivary glands and the completion of their development therein.

Kinghorn and Yorke[83] state that the predominant type of trypanosome in the intestine of infected G. morsitans was a large broad form, quite different from that which is most common in the salivary glands. The trypanosome in the glands resembles the short form seen in the blood of the vertebrate host. The authors quoted state that both the intestinal and salivary gland forms of infective G. morsitans are virulent when inoculated into healthy animals.

[83] Annals Trop. Med. and Parasitol., vii, p. 281.

Bruce and colleagues[84] have quite recently (June, 1914) published an account of their investigations of T. rhodesiense in G. morsitans in Nyasaland. (Incidentally it may be remarked that Bruce considers T. rhodesiense to be identical with a polymorphic strain of T. brucei--see pp. 83, 94). The development of T. rhodesiense takes place in the alimentary canal and salivary glands, not in the proboscis, of the tsetse fly. In feeding experiments with laboratory bred flies, as well as with a few wild flies, fed on infected dogs or monkeys, only 8 per cent. of the flies were found to be infected on dissection. Of such infected flies, however, only some allow of the complete development of the trypanosomes within them, in other words only about 1 per cent of the flies become infective. The length of time which elapses before a fly becomes infective varies from fourteen to thirty-one days, averaging twenty-three days, when kept at 84° F. (29° C.). The dominant intestinal type of flagellate in the fly is that seen in the proventriculus, which contains many long, slender trypanosomes. These proventricular forms find their way to the salivary glands, wherein crithidial and encysted forms are seen. They change into “blood forms,” which are short, stumpy trypanosomes and are infective. “The infective type of trypanosome in the salivary glands--corresponding to the final stage of the cycle of development--is similar to the short and stumpy form found in the blood of the vertebrate host.” The cycle is thus very similar to that of T. gambiense in G. palpalis (fig. 30).

[84] Proc. Roy. Soc., B, lxxxvii, p. 516.

CULTURE.--J. G. Thomson (1912),[85] and subsequently Thomson and Sinton, succeeded in cultivating T. rhodesiense in a modified Novy-MacNeal medium. The development obtained resembled that of the trypanosome in the intestine of Glossina.

[85] Annals Trop. Med. and Parasitol., vi, pp. 103, 331.

GENERAL NOTE ON TRYPANOSOMES WITH POSTERIOR NUCLEI.

Posteriorly placed nuclei have been found to occur not only in T. rhodesiense by Stephens and Fantham (1910), but also in T. pecaudi by Wenyon (1912), in T. brucei by Blacklock (1912), and in T. equiperdum by Yorke and Blacklock (1912).

Recently Stephens and Blacklock (1913)[86] have shown that two trypanosomes, different morphologically, have been confused under the name T. brucei. One of these is polymorphic (i.e., it exhibits long and slender as well as short and stumpy forms) and came from Uganda, while the other is monomorphic and is the original Zululand strain described by Bruce from cattle suffering from “nagana.” Bruce (1914) considers that morphological change has occurred in T. brucei in its passage through laboratory animals, and thus explains the diversity of views. The posterior nuclear forms described by Blacklock occurred in the Uganda strain of T. brucei. (See p. 95.) Similarly, a posterior nuclear form, T. equi, has been separated from T. equiperdum. (See p. 98.)

[86] Proc. Roy. Soc., B, lxxxvi, p. 187.

Again, Bruce and his colleagues on the Royal Society Commission investigating sleeping sickness in Nyasaland, have stated (April, 1913) that “evidence is accumulating that T. rhodesiense and T. brucei (Plimmer and Bradford) are identical.” The exact identity of trypanosomes showing posterior nuclei is, then, far from settled, although Laveran by cross immunity tests has declared that T. brucei is distinct from T. rhodesiense. No one has yet seen posterior nuclei in T. gambiense.

*Trypanosoma cruzi*, Chagas, 1909.

Syn.: Schizotrypanum cruzi, Chagas, 1909.

The trypanosome was discovered by Chagas[87] in the intestine of the bug, Triatoma (Conorhinus) megista, in Brazil, and then in the blood of a small monkey bitten by the bug. A little later it was found in the blood of a child, aged two years, suffering from irregular fever, extreme anæmia and enlarged glands in the State of Minas Geraes, Brazil. Chagas found that he was able to infect many of the usual laboratory animals with the trypanosome, by allowing the bug to bite them. He was also able to culture the parasite on blood agar.

[87] Mem. Inst. Oswaldo Cruz., i, p. 159.

Chagas found the Reduviid bug, Triatoma megista, in the houses of the poorer inhabitants of the Brazilian mining State, and that it attacked the people, more especially the children, at night, biting the face. On this account the insect is called “barbeiro” by the inhabitants. The bite is somewhat painful. The disease has since been found in other parts of Brazil, e.g., Matta de São João in Bahia province, Goyaz, Matto Grosso and São Paulo provinces, as well as in Minas Geraes.

Morphology.--The trypanosome has a large blepharoplast or kinetic nucleus. It is stated to occur both free and in the red blood corpuscles in the peripheral blood. It is about 20 µ long, on an average.

Two forms of the parasite (fig. 33, 6, 7) are described in the human blood. In one free form there is a large egg-shaped blepharoplast and the posterior (aflagellar) end of the parasite is drawn out. The blepharoplast (kinetic nucleus) may have a chromatin appendage. The nucleus is oval or band-like, containing a karyosome. The flagellum, starting close to the blepharoplast or its appendage, has a free portion of variable length. The other free form in the blood has a more or less round, terminal blepharoplast, smaller than in the first form, without a chromatin appendage as a rule. The body of this second form is decidedly broader than that of the first mentioned.

The dimorphism has been interpreted sexually, the first mentioned forms being termed males, the second ones females. The correctness of this interpretation is very doubtful.

No sign of longitudinal division was ever seen in the peripheral blood or in the internal organs. The “endocorpuscular” forms may be completely or partially enclosed in the red cell or only attached thereto (fig. 33, 1-5). At the beginning of infection the endocorpuscular forms are the more numerous. Some authorities, however, doubt these stages.

Life-history in the Vertebrate Host.--Chagas found fluctuations in the number of the parasites in the peripheral blood. He believes the increase of the parasites to be periodic.

The investigations of Chagas and of Hartmann have revealed two types of multiplication which take place in the internal organs of the vertebrate host.

(a) The first type--which possibly belongs to another organism, Pneumocystis carinii, see p. 90--occurs in the capillaries of the lungs. The flagellate parasite entering the lung capillaries loses its flagellum and undulating membrane. Its body becomes curved, and the two ends fuse, and so an oval mass is formed (fig. 33, 8-11). In some cases the blepharoplast disappears, in other cases it blends or fuses with the nucleus. The nucleus of the rounded parasite then divides into eight by successive divisions (fig. 33, 12-15). Next the body, which is surrounded by its own periplast, also divides, giving rise to eight tiny daughter individuals or merozoites (fig. 33, 15). The merozoites lie inside the periplast, which acts as a sort of “cyst wall.” The merozoites are said to exhibit dimorphism, and Chagas has interpreted the dimorphism in terms of sex. The daughter forms, produced by the parent trypanosomes which kept their blepharoplasts, themselves have blepharoplasts as well as nuclei, and have been termed “males” or “microgametes.” The merozoites, arising from parent trypanosomes which lost their blepharoplasts, have themselves only nuclei, and have been called “females” or “macrogametes.” In the case of the so-called “female” forms the single nucleus divides into two unequal parts, of which the smaller becomes the blepharoplast, and a flagellum is formed later. The so-called “males” possess early a rudiment of a flagellum. Both kinds of merozoites escape from the parent periplast wall, and enter red blood corpuscles. They grow into flagellates within the corpuscles, and then become free as adult trypanosomes in the blood-stream.

(b) The second mode of multiplication is one of asexual reproduction (schizogony or agamogony). It was first described by Hartmann from hypertrophied endothelial cells of the lungs. It has since been found in the cardiac muscle, in the neuroglia of the central nervous system, and in striped muscle (fig. 34). In laboratory animals it has also been found in the testicle and suprarenal capsules. In these tissues the parasite is intracellular, appearing as a small rounded body with nucleus and blepharoplast, without flagellum or undulating membrane. In other words the parasite is Leishmania-like in the body tissues, and recalls the organism of kala-azar.

Chagas considers this second mode of multiplication to be strictly asexual. By this means the number of parasites in the vertebrate host is increased, and symptoms are produced. On the other hand the first mode of multiplication, seen in the lung capillaries, is considered by Chagas to be a process of gametogony, in which sexual forms are differentiated. He finds that (1) the adult trypanosomes exhibit a dimorphism in human blood rarely seen in artificially infected guinea-pigs. In these guinea-pigs (infected from guinea-pigs) the so-called gametogony in the lungs is seldom seen. (2) The intermediate host, Triatoma (Conorhinus), becomes infective if fed directly on infected human blood, but very rarely so if fed on guinea-pigs. Chagas is led to believe that the occurrence of sexual forms constantly in the blood of man implies a greater resistance to infection on the part of man than on the part of guinea-pigs or other animals, assuming the general hypothesis that the formation of gametes represents a reaction of the Protozoön to unfavourable conditions. In human infection the number of parasites is always less than in laboratory animals, and their presence in the blood is transitory, lasting from fifteen to thirty days in acute cases. In many cases examination of the tissues at death has shown the presence of parasites in patients who did not exhibit them in the general circulation.

Life History in the Invertebrate Host.--About six hours after the ingestion of infected blood by the bug (Triatoma megista), the kinetic nucleus of the trypanosome moves towards the nucleus, and the flagellum is usually lost (fig. 35, 1-5). The parasite becomes rounded and Leishmania-like (fig. 35, 3-5), and multiplies rapidly by division. After a time, multiplication having ceased, the rounded forms become pear-shaped and develop a flagellum at the more pointed end. Crithidial forms (fig. 35, 7) are thus produced and pass into the intestine, where they multiply and may be seen in about twenty-five hours after the ingestion of blood. The crithidial forms may also be found in the rectum and fæces. The last stage in the invertebrate is a small, trypanosome-like type, long and thin with a band-like nucleus and conspicuous kinetic nucleus. These parasites are found in the hind gut and in the body cavity. They find their way into the salivary glands, and are the forms (fig. 36) which are transmissible to a new vertebrate host. The development in the bug takes about eight days altogether, after which time the bugs are infective.

There are thus three principal phases in the development of T. cruzi in Triatoma megista: (1) A multiplicative phase (Leishmania-like) in the stomach of the bug, (2) a crithidial phase, which is also multiplicative, in the hind-gut, and (3) a trypanosome phase, which is “propagative,” and apparently passes through the wall of the alimentary canal into the body cavity and so into the salivary glands.

Brumpt found that T. cruzi could live in Cimex lectularius, C. boueti, and Ornithodorus moubata. The Cimex fæces may be infective. Blacklock found multiplication of the parasite in C. lectularius.

Culture.--The trypanosome can be cultivated on Novy-MacNeal’s blood agar, and the cultural forms resemble those described in the bug.

Possible Reservoir.--Chagas thinks that probably the armadillo or “tatu” (Dasypus novemcinctus) may be the reservoir of T. cruzi. He also thinks that Triatoma geniculata is a transmitter; it lives in the burrows of the armadillo. Other carriers may be Triatoma infestans and T. sordida.

Clinical Features.--The trypanosomiasis of Brazil, produced by T. cruzi and spread by Triatoma spp. has received various names, such as oppilação, canguary, parasitic thyroiditis, and coreotrypanosis. It is also known as the human trypanosomiasis of Brazil, South American trypanosomiasis, and Chagas’ disease.

Chagas[88] reports two principal forms--acute and chronic. The acute infection is rare, and is characterized by increase in the volume of the thyroid gland, pyrexia, a sensation of crackling in the skin, enlarged lymphatic glands in the neck, axilla, etc., while the liver and spleen are increased in volume. Sclerosis of the thyroid gland is found at autopsy and fatty degeneration of the liver. During an attack of fever, trypanosomes are found in the blood. The acute form was only observed in children.

[88] Brazil Medico, Nov. 15, 1910. Longer account in Mem. Inst. Oswaldo Cruz, iii, pp. 219–275. See Sleep. Sick. Bull., Nos. 35 and 40.

In the chronic form Chagas reports several varieties: (a) A pseudo-myxœdematous form, occurring in most cases, especially up to the age of 15. There is hypertrophy of the thyroid gland or at least signs of hypothyroidism, general hypertrophy of glands, disturbance of heart rhythm, and nervous symptoms. (b) The myxœdematous form is characterized by similar symptoms, especially by considerable swelling of the thyroid body, and myxœdema of the subcutaneous cellular tissue; sometimes there is a true pachydermic cachexia. (c) In the nervous form there are motor disturbances, aphasia, disturbances of intelligence or signs of infantilism, athetosis of the extremities and idiocy. There are also paralytic symptoms of bulbar origin, disturbances of mastication, phonation and deglutition, and in some cases convulsive attacks. (d) The cardiac form, characterized by disturbance of the heart rhythm. In all these forms the parasite is found at autopsy in the nervous substance, brain, bulb and heart.

Vianna (1911)[89] has studied the histopathology of the disease. Some of the chief points are: in the heart muscle destruction of the sarcoplasm, followed by interstitial myocarditis; in the central nervous system invasion of the neuroglia cells and inflammatory reaction; in the suprarenal capsule invasion of medulla or cortex; inflammatory reaction can also be seen in the kidneys, the hypophysis and thyroid gland.

[89] Mem. Inst. Oswaldo Cruz, iii, p. 276.

Recently Chagas states[90] that “schizotrypanosomiasis” has been found in a child 15 to 20 days old, and that Trypanosoma cruzi has also been found in a fœtus--the mother being infected with the trypanosome. The trypanosomiasis can, then, be transmitted hereditarily.

[90] Rev. Med. S. Paulo (1912), xv, p. 337.

*Trypanosoma lewisi*, Kent, 1881.

The trypanosome has a nucleus somewhat displaced anteriorly, about one-third of the way from the anterior (flagellar) end of the body, a relatively straight edge to the undulating membrane, and a rod-shaped blepharoplast (fig. 37, A). It averages about 25 µ long and 1·5 µ broad.

Much attention has been devoted in recent years to the elucidation of the life history of the rat parasite, Trypanosoma lewisi. It is usually non-pathogenic to its host. It has been shown that the trypanosome can be transmitted from rat to rat by the rat-flea, Ceratophyllus fasciatus, and by Ctenocephalus canis (the so-called dog-flea). (See also p. 92). The flagellate may also persist, but doubtfully develop, in the rat-louse, Hæmatopinus spinulosus. These researches may now be summarized.

Life Cycle in the Vertebrate Host.--After infection of a rat, the trypanosomes usually appear in the animal’s blood in five to seven days. This incubation period applies either to a natural or an artificial infection. The trypanosomes first observed in the rat’s blood are diverse in form (fig. 37), being small, medium and large in size. This diversity is explained by the rapid multiplication taking place. A trypanosome may divide by equal longitudinal fission (fig. 37, C, D), but more commonly multiple fission occurs (fig. 37, G, H), and is unequal. Rosette forms are produced, in which the parent form can be recognized by its long flagellum (fig. 37, H) and attached to it are daughter individuals, smaller in size, from which flagella are growing. Minchin and J. D. Thomson (1912) find that the daughter forms may be set free sometimes with a crithidia-like facies (fig. 37, I), the blepharoplast being anterior but near to the nucleus. The daughter forms, when set free, may themselves divide by binary or multiple fission, in the latter case forming rosettes (fig. 37, K). Rosette forms were described by Moore, Breinl and Hindle in 1908.

Lingard, some years ago, described as a distinct species, T. longocaudense, certain forms with markedly elongate posterior ends (fig. 37, E). According to Minchin, “these forms appear to arise by binary fission” (fig. 37, D). These long drawn-out forms “are of constant occurrence and very numerous at a certain stage of the multiplication period.” It is about the eighth or tenth day after infection that the multiplication of T. lewisi is at its maximum in the rat’s blood. About the twelfth or thirteenth day the trypanosomes seen in the blood appear uniform. According to Minchin (1912)[91] the rat “gets rid of its infection entirely sooner or later, without having suffered, apparently, any marked inconvenience from it, and is then immune against a fresh infection with this species of trypanosome.” There is, then, a cycle of development in the vertebrate host. Minchin notes that the records of the pathogenicity of T. lewisi in rats, causing their death, need further investigation.

[91] “Protozoa,” p. 294.

T. lewisi inoculated into dormice (Myoxus nitela) and jerboas may become pathogenic thereto.

Carini found cysts in the lungs of rats infected with T. lewisi. He thought the cysts were schizogonic stages of the trypanosome, comparable with those found in the lungs of animals sub-inoculated with T. cruzi. Delanoë (1912)[92] has found, however, that such cysts, containing eight vermicules, occurred in rats uninfected with T. lewisi. Delanoë concludes that the pneumocysts are independent of T. lewisi, and represent a new parasite, Pneumocystis carinii. The pneumocysts may be allied to the Coccidia, and must be considered when investigating the life-cycle of a trypanosome in a vertebrate host. Some of the stages of T. cruzi may possibly be of this nature.

[92] C. R. Acad. Sci., clv, p. 658.

Life-cycle in the Invertebrate Host.--This occurs in fleas, and has been investigated in considerable detail by Minchin and Thomson in Ceratophyllus fasciatus, and by Nöller in Ctenocephalus canis and Ctenopsylla musculi.

When infected rat’s blood is taken up by the flea, the parasites pass with the ingested blood direct to the mid-gut of the Siphonapteran. In the flea’s stomach they multiply in a somewhat remarkable manner, namely, by penetration of the cells of the lining epithelium, and division inside the epithelial cells. Inside these lining cells the trypanosomes first grow to a large size and then form large spherical bodies, within which nuclear multiplication occurs (fig. 38, A-F). Any one of these large spherical bodies contains at first a number of nuclei, blepharoplasts and developing flagella, the original flagellum still remaining attached for a time. The cytoplasm then divides into daughter trypanosomes which are contained within an envelope, formed by the periplast of the parent parasite. Inside the periplast envelope are a number of daughter trypanosomes “wriggling very actively; the envelope becomes more and more tense, and finally bursts with explosive suddenness, setting free the flagellates, usually about eight in number, within the host-cell” (fig. 38, F). The daughter forms escaping from the host cell into the stomach lumen of the flea are fully formed, long trypanosomes.

The trypanosomes (fig. 38, G) pass into the flea’s rectum. The next phase is a crithidial one. The parasites become pear-shaped, in which the blepharoplast (kinetic nucleus) has travelled anteriorly past the nucleus towards the flagellum (fig. 39). The crithidial forms attach themselves to the wall of the rectum, and multiply by binary fission (fig. 39, D). A stock of parasites is thus formed which, according to Minchin and Thomson, “persist for a long time in the flea--probably under favourable conditions, for the whole life of the insect” (fig. 39, A-I).

From the crithidial forms of the rectum, according to Minchin, small infective trypanosomes arise by modification morphologically (fig. 39, J--M). The flagellum grows longer and draws out more the anterior part of the body, the blepharoplast migrates posteriorly, behind the nucleus, and carries with it the flagellar origin. These trypanosomes are small, but broad and stumpy (fig. 39, N), and can infect a rat. Minchin and Thomson formerly considered that the small, stumpy, infective trypanosomes pass forwards from the rectum into the stomach, and “appear to be regurgitated into the rat’s blood when the flea feeds.” However, the small infective trypanosomes were previously described by Swellengrebel and Strickland.[93] They may be found in the flea’s fæces. Nöller (1912)[94] has found that the development of T. lewisi proceeds quite well in the dog flea (Ctenocephalus canis) in Germany. Wenyon confirms this, and states that the human flea, Pulex irritans, and the Indian rat-flea, Xenopsylla cheopis, are also able to serve as true hosts for T. lewisi.

[93] Parasitology, iii, p. 360.

[94] Arch. f. Protistenkunde, xxv, p. 386.

Nöller stated that rats were not infected with T. lewisi by infective fleas biting them, but by the rats licking up the fæces passed by the fleas while feeding. This is not in agreement with Minchin and Thomson’s earlier views of regurgitation, which, apparently, they have now abandoned.[95] Wenyon (1912) confirms Nöller’s experiments. He took a dog flea, containing infective trypanosomes in its fæces, and allowed it to feed on a clean rat. The fæces of the flea, passed while feeding, were carefully “collected on a cover glass and taken up in culture fluid with a fine glass pipette.” The contents of the pipette were discharged into the mouth of a second clean rat. Injury to the rat’s mouth was carefully avoided. The first rat, on which the infective flea was fed, did not become infected, while the second rat, in whose mouth infective flea fæces were placed, became infected in six days.

[95] Report to Advis. Comm. Trop. Dis. Research Fund for 1913, p. 74.

When infective forms of T. lewisi have been developed within the gut of a rat flea, they may enter and infect the vertebrate host by[96] (a) being crushed and eaten by the rodent; (b) the rat may lick its fur on which an infected flea has just passed infective excrement; or (c) the rat may lick, and infect with flea excrement, the wound produced by the bite of the flea.

[96] Nuttall, Parasitology, v, p. 275.

The time taken for the full development of T. lewisi in the flea is about six days. The intracellular phase is at its height about the end of the first day; the crithidial phase, in the flea’s rectum, begins during the second day; the stumpy, infective trypanosomes are developed in the rectum about the end of the fifth day.

Wenyon[97] writes that, “the fleas, when once infected with T. lewisi, remain infected for long periods, for though many small infective trypanosomes are washed out of the gut at each feed, those that remain behind multiply to re-establish the infection of the hind gut. Further, the infection is still maintained even if the flea is nourished on a human being, so that fresh human blood does not appear to be destructive to the infective forms in the flea.”

[97] Report to Advis. Comm. Trop. Dis. Research Fund, October, 1912, p. 91. See also Journ. Lond. Sch. Trop. Med., ii, p. 119.

The best method of controlling fleas during experiments is that due to Nöller. He adopted the method of showmen who exhibit performing fleas, and secure them on very fine silver wire.

Of fleas fed on an infected rat only about 20 per cent. become infective. About 80 per cent. are immune. If fleas are examined twenty-four hours after feeding, trypanosomes will be found in all, so that many of the parasites are destined to degenerate.

It may be of interest to note that Gonder[98] (1911) has shown that a strain of T. lewisi resistant to arsenophenylglycin loses its resistance after passage through the rat-louse, Hæmatopinus spinulosus. These experiments suggest that physiological “acquired characters” may be lost by passage through an invertebrate host.

[98] Centralbl. f. Bakt., Orig., lxi, p. 102.

*Trypanosoma brucei*, Plimmer and Bradford, 1899.

Trypanosoma brucei was discovered by Sir D. Bruce in 1894 in cattle in Zululand and was named T. brucei by Plimmer and Bradford in 1899 in honour of its discoverer. This trypanosome is of considerable economic importance, as it is responsible for the fatal tsetse fly disease, or “nagana,” in cattle, horses and dogs. The disease is widely distributed in Africa and is transmitted from host to host by the tsetse, Glossina morsitans, and other species of Glossina. The virus is maintained in nature in certain big game, such as wildebeest, bushbuck and koodoo, which thus act as living reservoirs of disease from which the tsetse may become infected. These reservoir hosts are not injured, apparently, by the presence of the parasites.

T. brucei is rapidly fatal to the small laboratory animals, such as rats and mice. Horses, asses and dogs practically always succumb to its attacks, while a very small number of cattle recover from “nagana.” The disease is characterized by fever, destruction of red blood corpuscles, severe emaciation and by an infiltration of coagulated lymph in the subcutaneous tissue of the neck, abdomen and extremities giving a swollen appearance thereto. The natural reservoirs in which T. brucei has been long acclimatized are unaffected by the trypanosomes, while the newer hosts, such as imported cattle in Africa, are rapidly destroyed by their action.

The general morphology and life history in the vertebrate host is that of a typical trypanosome (fig. 40). Its length is from 12 µ to 35 µ, its breadth from 1·5 µ to 4 µ. Multiplication by longitudinal division proceeds in the peripheral blood (fig. 26), while latent, leishmaniform bodies are produced in the internal organs.

Bruce and colleagues[99] have quite recently (June, 1914) described the development of a Zululand strain of T. brucei in G. morsitans. The tsetse flies were bred out in Nyasaland. In vertebrate blood the brucei strain was polymorphic. The development was like that found for T. gambiense in G. palpalis (fig. 30), and by Bruce and colleagues for T. rhodesiense in G. morsitans in Nyasaland. Long trypanosomes were found in the proventriculus of the tsetse. Crithidial, rounded or encysted, and immature “blood forms” occurred in the salivary glands; and finally infective, stumpy, “blood forms” were differentiated in the salivary glands. The period of development of T. brucei in G. morsitans takes about three weeks, and then the fly becomes infective. Bruce believes that T. rhodesiense of Nyasaland and T. brucei of Zululand are the same, their cycles of development in G. morsitans being “marvellously alike.” (But see Laveran, p. 80.)

[99] Proc. Roy. Soc., B, lxxxvii, p. 526.

T. brucei has been cultivated with difficulty by Novy and MacNeal, using blood agar. The best treatment for nagana is arsenic in some form.

It is probable that more than one trypanosome has been confused under the name T. brucei, more especially as the occurrence of many species of trypanosomes in various animals in Africa was not suspected until comparatively recent times. It has been shown by Stephens and Blacklock (1913) that the original Zululand strain of T. brucei was monomorphic, while the organism sent from Uganda, and at the time believed by Bruce to be the same as the Zululand trypanosome, has been found to be polymorphic, with morphological resemblances to T. rhodesiense. Stephens and Blacklock[100] have suggested the name T. ugandæ for the polymorphic trypanosome, which, however, has marked resemblances with *Trypanosoma pecaudi*, and they are, perhaps, identical. T. pecaudi was the name given by Laveran[101] in 1907 to the causal agent of “baleri” in equines and sheep in the French Sudan. T. pecaudi, which is dimorphic, is widely distributed in Africa. An extremely small number of both T. pecaudi and T. ugandæ have been shown to possess posterior nuclei. T. pecaudi is transmitted by various species of Glossina, and is said to develop in the gut and proboscis of the fly.

[100] Proc. Roy. Soc., B, lxxxvi, p. 187.

[101] C.R. Acad. Sci., cxliv, p. 243.

On the other hand, Bruce and colleagues (1914), examining a strain sent from Zululand in 1913, state that T. brucei is polymorphic. Bruce (1914) suggests that passage through laboratory hosts has influenced and altered the morphology of the parasite.

*Trypanosoma evansi*, Steel, 1885.

Syn.: Spirochæta evansi, Steel, 1885; Hæmatomonas evansi, Crookshank, 1886; Trichomonas evansi, Crookshank, 1886.

Trypanosoma evansi, first found by Evans in 1880, in India, is the causal agent of the disease known as “surra.” The malady affects more particularly horses, mules, camels and cattle in India and neighbouring countries, such as Burma and Indo-China. It occurs also in Java, the Philippines, Mauritius and North Africa. Elephants may be affected. A serious outbreak among cattle in Mauritius occurred in 1902, the disease being imported into the island. The symptoms are fever, emaciation, œdema, great muscular weakness and paralysis culminating in death.

T. evansi varies from 18 µ to 34 µ in length and 1·5 µ to 2 µ in breadth. It has a pointed posterior extremity, and, anteriorly, there is a free portion to the flagellum (fig. 41). It is possibly monomorphic, but a few broad forms occur. The trypanosome multiplies by longitudinal fission in the blood. Rounded leishmaniform stages occur in the spleen of the vertebrate host, which stages Walker[102] (1912) considers to be phases of schizogony.

[102] Philippine Journ. Sc. (Sect. B), vii, p. 53.

The parasite is transmitted in nature by various species of Tabanus and Stomoxys, though at present little is known of the life-history within these invertebrate hosts.

Dogs are said to contract the disease by feeding on animals dead of surra.

A variety of T. evansi is the cause of “mbori” in dromedaries in Africa (Sahara and Sudan). Another possible variety, or closely allied form, is T. soudanense, the causal agent of “el debab” in camels and horses in North Africa, especially Algeria and Egypt.

An extraordinary example of the possible infection of a human being with an animal trypanosome is recorded in the case of Professor Lanfranchi, of the Veterinary School, Parma. The Professor became infected with trypanosomes, although only nagana and surra were maintained in his laboratory, and he himself had never visited the tropics. He suffered from irregular attacks of fever and was œdematous, but his mind remained clear. The identification of the trypanosome from Lanfranchi’s blood has been a matter of great difficulty. Apparently Mesnil and Blanchard (1914)[103] consider the strain found in the patient is almost indistinguishable in its reactions from T. gambiense, though the parasite is monomorphic. Lanfranchi considers that he was infected with T. evansi.

[103] Bull. Soc. Path. Exot., vii, p. 196.

*Trypanosoma equinum*, Voges, 1901.

Syn.: Trypanosoma elmassiani, Lignières.

Trypanosoma equinum was found by Elmassian to be the cause of the fatal disease, “mal de caderas,” of horses and dogs, in South America (Paraguay, Argentine, Bolivia). The name refers to the fact that in the disease, as in other trypanosomiases, the hind quarters become paralysed. Cattle are refractory to inoculation.

T. equinum is about 22 µ to 24 µ long and about 1·5 µ broad (fig. 42). Although this trypanosome is very active, yet it is characterized by the blepharoplast (kinetic nucleus) being very minute or even absent, as the granule sometimes seen may be the basal granule of the flagellum.

The mode of transmission of T. equinum is not known with absolute certainty. Migone has shown that the parasite causes a fatal disease in the large South American rodent, the capybara (Hydrochœrus capybara). This animal appears to be a reservoir of the parasite. Dogs may become infected by eating diseased capybaras, and it is suggested that the infection is spread from the dogs to horses by the agency of fleas. Some authorities consider that T. equinum may be spread by various Tabanidæ and by Stomoxys. Neiva (1913)[104] doubts all these modes of transmission in Brazil, and suggests Chrysops or Triatoma as vectors.

[104] Brazil Medico, xxvii, p. 366.

*Trypanosoma equiperdum*, Doflein, 1901.

Syn.: Trypanosoma rougeti, Laveran and Mesnil.

The malady of horses known as “dourine” or “mal du coït” is due to a trypanosome, T. equiperdum, discovered by Rouget in 1894. “Dourine”--also known as “stallion disease” or “covering disease”--is found among horses and asses in Europe, India, North Africa and North America. The trypanosome is transmitted by coitus, and so far as is known not by insect agency.

The progress of the disease may be considered under three periods. The period of œdema, when signs of œdema of the genitalia are seen. The œdema is generally painless and non-inflammatory. This period lasts about a month. It is succeeded by the period of eruption, which sets in about two months after infection. Circular œdematous areas (“plaques”), often about the size of a two-shilling piece, appear under the skin of the sides and hind quarters, and also, at times, under the skin of the neck, thighs and shoulders. The eruption is variable, but usually lasts about a week and leaves the animal in an enfeebled condition. Gland enlargement and swelling of the joints and synovia also may occur. The third period of the disease is described as that of anæmia and paralysis. The animal becomes very anæmic, emaciation is marked, superficial non-healing abscesses often form, and conjunctivitis and ulcerative keratitis can occur. Paralysis ensues, and in from two to eighteen months the animal dies. In the acute form of the disease the animal may die after the first period from acute paralysis.

It is difficult to find the trypanosomes in naturally infected animals, and they are best obtained from the plaques of the eruption. Apparently the parasite occurs more in the lymph than in the blood.

Ruminants are said to be refractory to this trypanosome.

T. equiperdum is about 25 µ to 28 µ in length on an average, but varies from 16 µ to 35 µ. Its cytoplasm is relatively clear, and does not show chromatic granules (fig. 43). It is stated to be monomorphic.

It has been shown recently by Blacklock and Yorke (1913)[105] that there is another trypanosome giving rise to dourine in horses. This trypanosome is dimorphic (resembling T. pecaudi and T. ugandæ), and is named T. equi. Previously T. equiperdum and T. equi had been confused.

[105] Proc. Roy. Soc., B, lxxxvii, p. 89.

Uhlenhuth, Hübner and Worthe have demonstrated the presence of endotoxins in T. equiperdum. These endotoxins may be set free by trypanolysis.

*Trypanosoma theileri*, Bruce, 1902.

This parasite, 60 µ to 70 µ long, and 4 µ to 5 µ broad, is distinguished for its large size, though it is not so large as T. ingens from Uganda oxen, whose length may be 72 µ to 122 µ, and breadth 7 µ to 10 µ. The posterior end of T. theileri is drawn out. Small forms of the flagellate are known, 25 µ to 53 µ in length. Probably other forms of the parasite have the nucleus posterior, and these flagellates were formerly separated as T. transvaaliense (Laveran, 1902). Myoneme fibrils may be seen on its body. The pathogenicity of this organism is doubtful, it was formerly thought to be the causal agent of “gall-sickness” in cattle in South Africa. T. theileri also occurs in Togoland, German East Africa, and Transcaucasia. Allied or identical parasites occur in cattle in India.

Trypanosoma theileri, specific to cattle, is perhaps transmitted by the fly Hippobosca rufipes in South Africa.

*Trypanosoma hippicum*, Darling, 1910.

Trypanosoma hippicum causes the disease of mules known as “murrina.”[106] It was found in mules imported to Panama from the United States. It can live in other equines. The parasite varies from 18 µ to 28 µ in length, and is from 1·5 µ to 3 µ broad. Its undulating membrane is little folded. The trypanosome has a noticeable blepharoplast. It can penetrate mucous membranes, and it is thought that the trypanosome may be transmitted during coitus. It may also be spread mechanically by species of Musca, Sarcophaga and Compsomyia, sucking the wounds of infected animals and carrying over the trypanosomes to wounds on healthy ones.

[106] Bull. Soc. Path. Exot., iii, p. 381.

*Endotrypanum schaudinni*, Mesnil and Brimont, 1908.

This organism was discovered in the blood of a sloth (Cholœpus didactylus), in South America (French Guiana).[107] It possesses special interest, in that the best known form of the organism is endoglobular, inhabiting the erythrocytes of the sloth. A free trypanosome in the same animal was considered to be different from the endoglobular form, which was somewhat like a peg-top, and possessed a short flagellum. Darling[108] (November, 1914) has seen the organism in Panama. He describes free crithidial forms in shed blood, but not in the blood-stream of the sloth.

[107] C. R. Soc. Biol., lxv, p. 581.

[108] Journ. Med. Research, xxxi, p. 195.

*Trypanosoma boylei*, Lafont, 1912.

This is a parasite of the Reduviid bug, Conorhinus rubrofasciatus. The insect attacks man in Mauritius, Réunion and other places. Lafont infected rats and mice by intraperitoneal injection with the gut-contents of infected bugs. Trypanosomes appeared in the mice. Other flagellate types were assumed by the parasites in the bug.

MONOMORPHIC TRYPANOSOMES.

A number of trypanosomes, characterized by relative uniformity in size and structure, may be considered under this heading. They occur in cattle, sheep, goats and horses in Africa, especially West Africa. Morphologically, they are characterized by the posterior (aflagellar) part of the body being swollen, while the anterior part narrows. The nucleus is central and situated at the commencement of the narrowing of the body. The blepharoplast is almost terminal, the undulating membrane is narrow and not markedly folded, so that the flagellar border lies close to or along the body. The flagellum may or may not possess a free portion.

Some recent workers have considered that T. brucei (Zululand strain) and T. evansi are also monomorphic, but they do not exhibit the general characteristics outlined above. T. brucei and T. evansi have already been considered separately.

The monomorphic trypanosomes, as defined above, include:--

*Trypanosoma vivax*, Ziemann, 1905.

This trypanosome[109] occurs in cattle, sheep and goats, and was first found in the Cameroons. It is fatal to cattle. Equines are also affected. Antelopes are the possible reservoirs of the trypanosome. It is probably transmitted by Glossina palpalis and other tsetse flies. Its movement is very active. It possesses a free flagellum (fig. 45) and it averages 23 µ to 24 µ in length. T. cazalboui (Laveran, 1906)--the causal agent of “souma” in bovines and equines in the French Sudan--is probably synonymous with T. vivax.

[109] See Bruce and colleagues (1910), Proc. Roy. Soc., B, lxxxiii, p. 15.

*Trypanosoma capræ* (Kleine, 1910) is allied, but is somewhat broader and more massive. It was found in goats in Tanganyika.

*Trypanosoma congolense*, Broden, 1904.

Probable synonyms.--Trypanosoma dimorphon, Laveran and Mesnil, 1904; Trypanosoma nanum, Laveran, 1905; Trypanosoma pecorum, Bruce, 1910; Trypanosoma confusum, Montgomery, 1909.

This trypanosome causes disease among horses (e.g., Gambia horse sickness), cattle, sheep, goats, pigs, and dogs. It is widely distributed in Central Africa (e.g., Gambia, Congo, Uganda, Nyasaland), the strain probably being maintained naturally in big game. It is transmitted by various Glossinæ, and perhaps by Tabanus and Stomoxys. It is said to develop in the gut and proboscis of Glossina palpalis and G. morsitans. The trypanosome averages 13 µ to 14 µ in length and has no free flagellum (fig. 46). It is about 2 µ broad. Formerly T. nanum and T. pecorum were said to differ in their pathogenicity, the former being said not to infect the smaller laboratory animals. Yorke and Blacklock (1913), however, consider that the virulence varies and that these trypanosomes are probably the same.

The T. dimorphon originally obtained by Dutton and Todd (1903) in Gambian horse sickness has been shown to be a mixture of T. vivax and T. congolense.

*Trypanosoma simiae* (T. ignotum) is like T. congolense. It averages 17·5 µ long. It is virulent to monkeys and pigs.

*Trypanosoma uniforme*, Bruce, 1910.

This trypanosome was found in oxen in Uganda.[110] It can be inoculated to oxen, goats and sheep, but is refractory to dogs, rats and guinea-pigs. It has been found in antelopes. It resembles T. vivax, but is smaller (fig. 47), averaging 16 µ in length. A free flagellum is present. It is transmitted by Glossinæ.

[110] Proc. Roy. Soc., B, lxxxiii, p. 176.

Many other trypanosomes occur in mammals, while birds, reptiles, amphibia (fig. 48) and fish also harbour them. The discussion of these forms does not come within the scope of the present work. They are dealt with in Laveran and Mesnil’s “Trypanosomes et Trypanosomiases,” 2nd edit., 1912.

GENERAL NOTE ON DEVELOPMENT OF TRYPANOSOMES IN GLOSSINA.

Before concluding the account of trypanosomes, it may be of interest to remark that several African trypanosomes develop in various species of Glossina, and are found in different parts of the alimentary tract and in the proboscis. Thus (a) T. vivax, T. uniforme and T. capræ develop in the fly’s proboscis (labial cavity and hypopharynx) only; (b) T. congolense, T. simiæ and T. pecaudi develop first in the gut of the fly and then pass forward to its proboscis; and (c) T. gambiense and T. rhodesiense develop first in the gut and later invade the salivary glands of the tsetse. The proboscis or the salivary glands in such cases are termed by Duke[111] the anterior station of the trypanosome, wherein it completes its development.

[111] Repts. Sleeping Sickness Commission Roy. Soc. (1913), xiii, p. 82.

ADAPTATION OF TRYPANOSOMES.

These flagellates may exhibit power of adaptation to changes of environment, such as those due to the administration of drugs, change of host, etc. A few examples of such mutations may be briefly considered:--

(1) Blepharoplastless Trypanosomes.--T. brucei may become resistant to pyronin and oxazine. Accompanying this drug resistance is a change in morphology, namely, the loss of the blepharoplast (Werbitzki).[112] A race or strain of blepharoplastless trypanosomes may be thus produced which retains its characteristic feature after as many as 130 passages (Laveran).[113] Oxazine is the more powerful drug, and it acts directly on the blepharoplast. (Compare the natural blepharoplastless character of T. equinum.)

[112] Centralbl. f. Bakt. (1910), Orig., liii, p. 303.

[113] Bull. Soc. Path. Exot., iv, p. 233.

(2) Reference has been made on p. 93 to the experiments of Gonder, who showed that a strain of T. lewisi rendered resistant to arsenophenylglycin lost its resistance after passage through the rat louse. This is in marked contrast with the retention of drug resistance during passage by inoculation from rat to rat.

(3) T. lewisi from the blood of a rat when transferred to a snake seems largely to disappear, as very few flagellates are seen. When blood from the snake is inoculated into a clean rat, then trypanosomes reappear in the rat, but they are not all like those originally inoculated. It seems certain that, in such a case, changes in form and virulence of the trypanosome have occurred. Similar experiments were made with T. brucei from rats to adders and other animals and back to rats. Changes in the form and virulence of T. brucei occurred.

These interesting experiments were performed by Wendelstadt and Fellmer.[114]

[114] Zeitschr. f. Immunitatsforschung, iv, p. 422 (1909), and v, p. 337 (1910).

Genus. *Herpetomonas*, Saville Kent, 1881.

Herpetomonas is a generic name for certain flagellates possessing a vermiform or snake-like body, a nucleus placed approximately centrally, and a blepharoplast (kinetic nucleus) near the flagellar end. There is no undulating membrane (fig. 49, a). The organisms included in this genus certainly possess one flagellum, while according to Prowazek (1904) Herpetomonas muscæ-domesticæ, the type species, possesses two flagella united by a membrane. Patton,[115] Porter[116] and others affirm, however, that the biflagellate character of H. muscæ-domesticæ (from the gut of the house-fly) is merely due to precocious division. The matter is further complicated by the generic name Leptomonas, given by Kent in 1881, to an uniflagellate organism found by Bütschli in the intestine of the Nematode worm, Trilobus gracilis. This parasite, Leptomonas bütschlii, has not yet been completely studied. Until these controversial points relating to the identity or separation of Herpetomonas and Leptomonas have been satisfactorily settled, we may retain the better known name Herpetomonas for such uniflagellate, vermiform organisms. However, the name Leptomonas, having been used by Kent two pages earlier in his book (“Manual of the Infusoria”) than Herpetomonas, would have priority if the two generic names were ultimately shown to be synonymous.

[115] Arch. f. Protist., xiii, p. 1.

[116] Parasitology, ii, p. 367.

A full discussion of these interesting and important flagellates hardly comes within the purview of the present work; brief mention can only be given here to certain species.

The Herpetomonads occur principally in the digestive tracts of insects, such as Diptera and Hemiptera. They are also known in the guts of fleas and lice, but are not confined to blood-sucking insects. One example, H. ctenocephali (Fantham, 1912)[117] occurs in the digestive tracts of dog fleas, Ctenocephalus canis, in England, France, Germany, Italy, India, Tunis, etc. It is a natural flagellate of the flea, and might easily be confused with stages of blood parasites in the gut of the dog flea. Dog fleas are stated by Basile to transmit canine kala-azar, which is believed to be the same as human infantile kala-azar. Confusion is further likely to arise since herpetomonads pass through pre-flagellate, flagellate and post-flagellate or encysted stages; pre- and post-flagellate stages being oval or rounded and Leishmania-like. The post-flagellate stages are shed in the fæces, and are the cross-infective stages by means of which new hosts are infected by the mouth. The possible presence of such natural flagellates must always be considered when experimenting with fleas, lice, mosquitoes, etc., as possible vectors of pathogenic flagellates like Leishmania and Trypanosoma. H. pediculi (Fantham, 1912) occurs in human body lice.[118] See further remarks on pp. 107, 112.

[117] Bull. Path. Exot., vi, p. 254.

[118] Proc. Roy. Soc., B, lxxxiv, p. 505.

Laveran and Franchini (1913–14)[119] have recently succeeded in inoculating Herpetomonas ctenocephali, from the gut of the dog flea, intraperitoneally into white mice, and producing an experimental leishmaniasis in the mice. A dog was also infected. They have also succeeded in infecting mice with H. pattoni--a natural flagellate of the rat flea--by mixing infected rat fleas with the food of the mice, and by causing them to ingest infected fæces of rat fleas. Further, they have shown that infection with the herpetomonas occurs naturally by this method, that is, by the rodents eating the fleas and not by the insects inoculating the flagellates into the vertebrates when sucking blood. These experiments shed an interesting light on the probable origin of Leishmania and its cultural herpetomonad stage, which were very probably once parasitic flagellates in the gut of an insect.

[119] C. R. Acad. Sci., clvii, pp. 423, 744. Ibid., clviii, pp. 450, 770. Bull. Soc. Path. Exot., vii, 605.

Fantham and Porter[120] (1914–15) have shown that young mice may be inoculated or fed with Herpetomonas jaculum, from the gut of the Hemipteran, Nepa cinerea (the so-called “water-scorpion”), with fatal results. The pathogenic effects are like those of kala-azar. They also showed that the post-flagellate stages of the herpetomonads seemed most capable of developing in the vertebrate.

[120] Proc. Camb. Philosoph. Soc., xviii, p. 39.

A herpetomonad, H. davidi, has been found in the latex of species of the plant-genus Euphorbia in Mauritius, India, Portugal, etc. It is apparently transmitted to the plants by Hemiptera. The plants sometimes suffer from “flagellosis.”

Franchini (1913)[121] has described a new parasite, Hæmocystozoon brasiliense, from the blood of a man who had lived in Brazil for many years. It possesses flagellate and rounded stages, and is closely allied to the herpetomonads.

[121] Bull. Soc. Path. Exot., vi, pp. 156, 333, 377.

Genus. *Crithidia*, Léger, 1902, emend. Patton, 1908.

Crithidia is the generic name of vermiform flagellates with a central nucleus, a blepharoplast or kinetic nucleus in the neighbourhood of the principal nucleus, and a rudimentary undulating membrane bordered by a flagellum arising from a basal granule, which is the centrosome of the kinetic nucleus (fig. 49_b_). The anterior or flagellar end of the body is attenuated and fades off as the undulating membrane.

Crithidia fasciculata, the type species, was found by Léger in the alimentary canal of Anopheles maculipennis. Crithidia occur in bugs, flies, fleas,[122] and ticks. Some of them are found in the body-fluid of the invertebrate host as well as in the gut. Others may be restricted to the body cavity or intestine respectively. C. melophagia from the sheep-ked, Melophagus ovinus, and C. hyalommæ from the hæmocœlic fluid of the tick, Hyalomma ægyptium, pass into the ovaries and eggs of their hosts, and the young keds or ticks are born infected.

[122] See Porter, Parasitology, iv, p. 237.

C. fasciculata has been shown by Laveran and Franchini to be inoculable into white mice, producing a sort of experimental leishmaniasis therein. In one case cutaneous lesions were produced like those of Oriental sore.

Crithidia are natural flagellates of Arthropoda, with their own pre-flagellate, flagellate and post-flagellate stages, and must not be confused with transitory crithidial stages of trypanosomes.

Genus. *Leishmania*, Ross, 1903.

With an oval body containing nucleus and blepharoplast (kinetic nucleus) but no flagellum. An intracellular parasite in the vertebrate host.

Included in the genus Leishmania are three species, namely:--

(1) Leishmania donovani, Laveran and Mesnil, 1903, the parasite of Indian kala-azar, a generalized systemic disease, usually fatal, occurring in subjects of all ages. (2) Leishmania tropica, Wright, 1903, the parasite of Delhi boil, Oriental sore, Aleppo button--a localized, cutaneous disease, usually benign. (3) Leishmania infantum, Nicolle, 1908, the parasite of infantile kala-azar, occurring in children (and a few adults) around the shores of the Mediterranean. The disease is perhaps a form of Indian kala-azar, and the parasite is probably identical with L. donovani.

These diseases may be termed collectively leishmaniases. The morphology of the various species is practically identical.

*Leishmania donovani*, Laveran and Mesnil, 1903.

Syn.: Piroplasma donovani, Laveran and Mesnil.

The parasite of Indian kala-azar was demonstrated in 1900 by Leishman from a post-mortem examination of a case of “Dum-Dum fever,” but details were not published till May, 1903. In July, 1903, Donovan found similar bodies from cases in Madras. Rogers succeeded in cultivating the parasite in July, 1904.[123] The original centre of the disease was probably Assam; it occurs also in Madras, Ceylon, Burma, Indo-China, China and Syria. A variety of this leishmaniasis is found in the Sudan. The patient becomes emaciated, with a greatly enlarged spleen. There is anæmia and leucopenia.

[123] The literature up to 1912, on kala-azar and other leishmaniases is reviewed in the Kala-azar Bulletin. Afterwards in the Tropical Diseases Bulletin.

The parasite, commonly known as the Leishman-Donovan body, is intracellular (fig. 50, 2, 3). It is found in the endothelial cells of the capillaries of the liver, spleen, bone-marrow, lymphatic glands and intestinal mucosa, and in the macrophages of the spleen and bone-marrow. Some host cells may contain many parasites. It is rather rare in the circulating blood, but may be found in the blood from the femoral, portal and hepatic veins. It does not occur in the red blood corpuscles as was formerly thought. The parasites liberated from the endothelial cells are taken up by the mononuclear and polymorphonuclear leucocytes. The Leishman-Donovan body is the resting stage of a flagellate. As found in man it is a small, oval organism, about 2·5 µ to 3·5 µ in length by 2 µ in breadth, and containing two chromatinic bodies, corresponding to the nucleus and kinetic nucleus (blepharoplast) of a flagellate. The latter element is the smaller and more deeply staining, and is usually placed at the periphery, transversely to the longer axis of the oval organism. There is sometimes a very short, slightly curved filament to be seen, which may be a rhizoplast. Multiplication takes place by binary or multiple fission. The presence of the parasite used to be demonstrated by splenic or hepatic puncture; nowadays it can be demonstrated in peripheral blood, e.g., of the finger, or by culture of infected blood.

L. donovani can be cultivated in citrated splenic blood, under aerobic conditions, at 22° to 25° C. This was first accomplished by Rogers (1904). It is not so easily culturable as L. infantum on the Novy-MacNeal-Nicolle medium.[124] L. donovani is inoculable with some difficulty into experimental animals--in India, white rats, white mice, dogs and monkeys (Macacus spp.), have been inoculated. The Sudan variety, somewhat less virulent, is inoculable to monkeys. Row also produced a local lesion in Macacus sinicus by subcutaneous inoculation of L. donovani. Parasites taken from such a local lesion were found to be capable of producing a generalised infection in Macacus sinicus and white mice.

[124] For the composition of this medium, see Appendix.

In cultures the various species of Leishmania all grow into herpetomonad, uniflagellate organisms (fig. 50, 10), about 12 µ to 20 µ in body length. On this account Rogers[125] and Patton place the Leishman-Donovan body within the genus Herpetomonas. The method of culture may be used in diagnosing leishmaniases.

[125] Proc. Roy. Soc., B, lxxvii, p. 284.

Kala-azar is very probably an insect-borne disease. Patton[126] suspects the bed-bug to be the transmitter and finds (fig. 50, 4-6) that the Leishman-Donovan body can develop into the flagellate stage in the digestive tract of the bed-bug. Feeding experiments are unsatisfactory, since there are very few cases in which the parasites occur in sufficient numbers in the peripheral blood to make the infection of the insect possible, or at any rate easy. In examining the alimentary tracts of insects for possible flagellate stages of Leishmania, it must be remembered that in many insects natural flagellate parasites, belonging to the genus Herpetomonas, may occur therein; such natural insect flagellates may be harmless, and have no connection with the life-cycle of L. donovani. Natural herpetomonads are known to occur in the alimentary tracts of flies, mosquitoes, sand-flies, fleas and lice, but not in bed-bugs. Further, if such flagellates are able to be inoculated into and live within vertebrate hosts, producing symptoms like those of leishmaniasis, the origin of kala-azar is indicated (see pp. 104, 112).

[126] Sci. Mem. Govt. India, Nos. 27, 31 (1907–08).

*Leishmania tropica*, Wright, 1903.

Syn.: Helcosoma tropicum, Wright, 1903; L. wrighti, Nicolle, 1908; Ovoplasma orientale, Marzinowsky and Bogrow.

It is believed by some that the parasite was first described by Cunningham in 1885, and studied by Firth in 1891, being called by him Sporozoon furunculosum. If these earlier studies were of the parasite, then its correct name is L. furunculosa, Firth, 1891.

The benign disease produced by this parasite has received many names, among the best known being Oriental sore, Tropical sore, Delhi boil and Aleppo button. These names, however, are not happy ones, as cutaneous leishmaniasis (e.g., on the ear) is now known to occur in the New World, for example in Mexico, Venezuela, Brazil and neighbouring States. However, it may be necessary to subdivide cutaneous leishmaniases later.

In the Old World the disease occurs in India, Persia, Arabia and Transcaucasia. It is also known in Algeria, Northern Nigeria, Egypt, Sudan, Crete, Calabria, Sicily and Greece.

The boils often occur on the face, and before ulceration the parasites may be found in the cells at the margin and floor of the “button.” In searching for parasites the scab should be removed and scrapings made from the floor and edges. Where lesions occur atrophy of the epidermis takes place, and infiltration of mononuclear cells (e.g., plasma cells, lymphoid and endothelial cells) follows. The parasites are intracellular, being found inside mononuclear cells. In non-ulcerating sores, Cardamitis found some free parasites. Non-ulcerating forms are said to occur in the Sudan. In the Old World the sores are often limited to exposed surfaces of the body. Infection of mucous membranes (such as the lip, palate, buccal and nasal membranes) may occur, especially in South America, and are often known there as “Espundia.” Christopherson (1914) has recorded a case in Khartoum.

Leishmania tropica is equally well cultivated on Novy-MacNeal-Nicolle medium or on citrated blood. The usual temperature for cultivation is 22° to 28° C., though Marzinowski claims to have cultivated the parasite at 37° C. L. tropica can be inoculated into monkeys and dogs, with the production of local lesions. Material from a human sore or flagellates from a culture may be thus successfully inoculated. Also infected material may be rubbed directly into a scarified surface. The incubation period is long, extending over several months. The duration of the disease may be from twelve to eighteen months. Recovery from one attack of tropical sore confers immunity, and the Jews in Bagdad inoculate their children with the disease on a part of the body which will be covered, and so secure immunity in adult life.

The mode of transmission of L. tropica is unknown. Wenyon (1911)[127] has found that the parasite develops into the flagellate stage in the digestive tract of Stegomyia fasciata in Bagdad. Patton (1912)[128] has found similar development in the bed-bug in Cambay. The house-fly, Phlebotomus and Simulium have been suspected as transmitters in different parts of the world.

[127] Parasitology, iv, p. 387.

[128] Sci. Mem. Govt. India, No. 50.

An interesting announcement has been made recently (May, 1913), that Neligan has found that L. tropica occurs in dogs in Teheran, Persia, producing ulcers on the dogs’ faces (cf. natural occurrence of L. infantum in dogs--see p. 110). Yakimoff and Schokhor (1914),[129] have found the disease in dogs in Tashkent.

[129] Bull. Soc. Path. Exot., vii, p. 186.

Gonder[130] (1913) has performed some interesting experiments showing the relation of infantile kala-azar to Oriental sore. Gonder infected mice with L. infantum and with L. tropica. He used culture material and injected intraperitoneally or intravenously. In each a general infection resulted, with enlargement of the liver and spleen. Later, however, mice injected with Oriental sore (North African variety) developed peripheral lesions on the feet, tail and head, and the lesions contained Leishmania. No such peripheral lesions developed in the case of the mice infected with the kala-azar virus. Gonder suggested that Oriental sore, like kala-azar, is really a general infection overlooked in its earlier stages, and that it is in the later stages that peripheral lesions on the skin are developed. Row (1914)[131] also obtained a general infection in a mouse by the injection of cultures of L. tropica from Oriental sore of Cambay.

[130] Arch. f. Schiffs- u. Trop. Hyg., xvii, p. 397.

[131] Bull. Soc. Path. Exot., vii, p. 272.

*Leishmania infantum*, Nicolle, 1908.[132]

Infantile splenic anæmia has been long known in Italy. It also occurs in Algeria, Tunis, Tripoli, Syria, Greece, Turkey, Crete, Sicily, Malta,[133] Spain and Portugal. This leishmaniasis is, then, distributed along the Mediterranean littoral; also in Russia. Cathoire (1904) in Tunis and Pianese (1905) in Italy were among the first to see the parasite. Nicolle then found the parasite in patients in Tunis, and further found spontaneous infection in dogs. The patients are usually children between the ages of 2 and 5 years. There are a few cases known in which the infantile type of leishmaniasis occurred in youths and adults of the ages of 17 to 19, while one patient in Calabria was 38 years old. The symptoms are like those of Indian kala-azar. Several Italian investigators and others consider that L. infantum is the same as L. donovani, and that the latter name should be used for the parasite of Mediterranean leishmaniasis. This view, as to the identity of L. donovani and L. infantum, seems coming into general favour.

[132] Arch. Inst. Pasteur Tunis, i, p. 26.

[133] See Wenyon (1914), Trans. Soc. Trop. Med. and Hyg., vii, p. 97; also Critien (1911), Annals Trop. Med. and Parasitol., v, p. 37.

There are, however, differences between the Indian and infantile kala-azars, in addition to the ages of the patients affected, thus: (a) As regards cultures, it is found that L. infantum is readily grown on the Novy-MacNeal-Nicolle (“N.N.N.”) medium (saline blood-agar), and that sub-cultures are easily obtained; in citrated blood L. infantum grows with difficulty. The reverse is the case with regard to culture media for L. donovani, which grows with difficulty on the N.N.N. medium, but relatively easily in citrated splenic blood. (b) Considering inoculability into experimental animals, it is found that L. donovani is inoculated generally with some difficulty into white rats, white mice and monkeys, and with greater difficulty into dogs, while L. infantum can be inoculated into several experimental animals, especially into dogs and monkeys, with ease. (c) At present L. donovani is not known to occur spontaneously in animals, but L. infantum is found naturally in dogs in the Mediterranean region, and the disease in dogs is often referred to as canine kala-azar. Kittens have occasionally been found infected. However, these differences must not be emphasized too much.

The material for cultivation is obtained from punctures of spleen, liver or bone-marrow of cases infected with L. infantum. It is not always easy, however, to infect from cultures, as the cultural flagellates inoculated into the body are often phagocytosed.

Similarly, the material for animal inoculation is obtained from emulsions of infected spleen, liver or bone-marrow. Dogs and monkeys are easily inoculated with such material; Nicolle inoculates into the liver or the peritoneal cavity. Mice, white rats, guinea-pigs and rabbits only show slight infections after such inoculations.

Dogs infected experimentally with infantile leishmaniasis may show either acute or chronic symptoms. The acute course occurs more often in young dogs, and is usually fatal in three to five months. The chronic course is found more commonly in older dogs, and may last seventeen to eighteen months. In acute forms there is irregular fever, progressive wasting, diarrhœa occasionally, motor disturbances involving the hind quarters, and the animal dies in a comatose condition. In the chronic form the animal may appear well, except for loss of weight. The parasites may be found in the internal organs of these experimental dogs, but are not numerous in the peripheral blood except at times of high fever. Experimental monkeys live about three months.

It may be interesting to record the number of dogs found to be infected naturally with leishmaniasis in various countries. In Tunis, Nicolle and Yakimoff found about 2 per cent. infected out of about 500 dogs examined. Sergent in Algiers found 9 infected out of 125 dogs examined. In Italy and Sicily, Basile found about 40 per cent. of the dogs to be infected out of 93 examined at Rome and Bordonaro. Cardamitis found 15 infected out of 184 examined in Athens. In Malta, Critien found 3 infected out of 30 dogs examined. Alvares found 1 infected dog out of 19 examined in Lisbon. Pringault has recently (December, 1913) found an infected dog in Marseilles.[134] Yakimoff and Schokhor found 24 per cent. infected out of 647 dogs examined in Turkestan.

[134] Bull. Soc. Path. Exot., vii, p. 41.

The distribution of the parasites in the body of the human patient is much the same as in the case of Indian kala-azar. Critien records the finding of parasites in the mucous flakes of the stools of a three-year-old Maltese child.[135] Intestinal lesions rarely occur in infantile leishmaniasis.

[135] Quoted by Leishman (1911) in his interesting review of Leishmaniasis, Journ. Roy. Army Med. Corps, xvii, p. 567, xviii, pp. 1, 125. Also Quart. Journ. Med. v, pp. 109–152.

Ætiology.--Infantile leishmaniasis is stated to be transmitted by fleas, especially dog fleas, Ctenocephalus canis (= Pulex serraticeps), and by Pulex irritans. Children living in contact with infected dogs may be bitten by infected dog fleas, and so contract the disease. Basile (1910–11) and Sangiorgi (1910) state that they found L. infantum parasites in the digestive tract of the dog flea. After searching they found infected dog fleas on the beds, mattresses, and pillows used by children suffering from the disease. Franchini (1912) thinks that Anopheles maculipennis may be concerned in the transmission.

Basile[136] tried a number of experiments to show that infantile leishmaniasis is transmitted by fleas, thus:--

[136] Numerous papers in Rendiconti R. Accad. dei Lincei (Rome), xix, xx (1910–11).

(1) Fleas were taken from a healthy dog. They were placed in vessels containing infected spleen-pulp and allowed to feed thereon. The fleas were then killed and dissected, and portions of the gut-contents examined for parasites. The remainder of the gut was emulsified and injected into a young puppy, whose bone-marrow had been shown previously to be uninfected. Basile states that the puppy became infected. The parasites are said to increase in number in the flea’s gut.

(2) Two healthy pups, each a month old, and born in the laboratory, were placed in a disinfected, flea-proof cage. A few days after, an infected dog was placed in the cage, so that fleas from the infected dog could pass on to the puppies. A month later the two pups became infected, parasites being found in them after liver puncture. A number of control puppies from the same litter remained uninfected and in good health.

(3) Basile next used other laboratory-born puppies, a month old. Four of the litter were placed in a disinfected, flea-proof gauze cage in Rome. The cage was isolated from other dogs. Fleas obtained from an infected area in Sicily were placed in the cage. The puppies were examined by hepatic puncture, but were found to be negative for two months. Then two of the puppies showed infection, and six days later the remaining two puppies were found to be infected, and all four died. They showed irregular temperatures, and were getting thin. Control puppies remained healthy.

From these experiments Basile concludes that fleas transmit leishmaniasis. However, Basile did not exclude the possible occurrence of natural herpetomonads in the gut of the fleas.[137] Herpetomonas ctenocephali is known to occur in the gut of Ctenocephalus canis. A natural Herpetomonas is also known in the gut of Pulex irritans, as well as a Crithidia (C. pulicis, Porter). These natural flagellates of the fleas pass through non-flagellate stages, like the Leishman-Donovan body. In consequence Wenyon and Patton, among others, have criticized Basile’s results. Further, other investigators, such as Wenyon and Da Silva (1913), have repeated Basile’s flea experiments and been unable to confirm them.

[137] See Fantham, Brit. Med. Journ., 1912, ii, p. 1196.

In feeding and inoculation experiments the incubation period of the parasite may be long, and so it is necessary to wait a long time to see whether the parasite will develop.

Immunity.--Nicolle has tried some experiments with L. infantum and L. tropica. He finds that in animals recovery from an attack of the former confers immunity against infection by the latter and vice-versâ.

Laveran[138] records that a monkey having an immunity against L. infantum was also immune to L. donovani.

[138] Annales Inst. Pasteur (1914–15), xxviii, pp. 823, 885; xxix, pp. 1, 71.

As mentioned on p. 103, Laveran and Franchini (1913), working in Paris, have succeeded in inoculating Herpetomonas ctenocephali, a natural flagellate in the gut of the flea, Ctenocephalus canis, into white mice. Leishmaniform stages of the flea flagellate were recovered from the peritoneal exudate, blood and organs of the mice some weeks after inoculation. The parasites may also be conveyed by way of the digestive tract of the vertebrate. Similar experiments have succeeded with H. pattoni. These experiments go to show, together with those of Fantham and Porter with H. jaculum (see p. 104), that, in the words of the latter authors, “it may be expected that the various leishmaniases, occurring in different parts of the world, will prove to be insect-borne herpetomoniases.”

Genus. *Histoplasma*, Darling, 1906.

Under the name Histoplasma capsulatum,[139] Darling described small round or oval parasites, enclosed in a refractile capsule, and each containing a single nucleus. The bodies were found in cases of splenomegaly in Panama. They occurred in the endothelial cells of the small blood-vessels of the liver, spleen, lungs, intestine and lymphatic glands, and also within the leucocytes. A few flagellates were stated to occur in the lungs. The parasite has usually been placed near Leishmania, but recently Rocha-Lima has stated that Histoplasma is a yeast.

[139] Journ. Amer. Med. Assoc., xlvi, p. 1283: Journ. Exptl. Med. (1909), xi, p. 515.

Genus. *Toxoplasma*, Nicolle and Manceaux, 1908.

The genus was created for crescentic, oval or reniform parasites, 2·5 µ to 6 µ by 2 µ to 3 µ, possessing a single nucleus and multiplying by binary fission. They occur in mononuclear and polymorphonuclear cells in the blood, spleen, liver, peritoneum etc. (fig. 51). The parasites have been found in the gondi, dog, rabbit, mole, mouse, pigeon and other birds. Although various species names have been given to the parasites in these hosts, it seems probable, from cross infection experiments, that there is but one species with several physiological races. Splendore[140] (1913) has described a flagellate stage.

[140] Bull. Soc. Path. Exot., vi, p. 318.

Castellani (1913–14)[141] has described similar parasites from a case of splenomegaly, with fever of long standing, in a Sinhalese boy. The bodies were found in the spleen and more rarely in the blood (fig. 52). Castellani has named them Toxoplasma pyrogenes. Further researches are needed.

[141] Journ. Trop. Med. and Hyg., xvii, p. 113.

THE SPIROCHÆTES.

The Spirochætes are long, narrow, wavy, thread-like organisms, with a firm yet flexible outer covering or periplast. There is a diffuse nucleus internally in the form of bars or rodlets of chromatin distributed along the body. In some forms there is a membrane or crista present (fig. 53), which in the past was compared with the undulating membrane of a trypanosome, but the membrane of a spirochæte does not undulate. Progression is very rapid, corkscrew-like and undulatory movements occurring simultaneously.

The genus Spirochæta was founded by Ehrenberg in 1833 for an organism which he discovered in stagnant water in Berlin. Ehrenberg named the organism Spirochæta plicatilis. According to Zuelzer (1912) S. plicatilis does not possess a membrane or crista, but an axial filament. S. gigantea has been described by Warming from sea-water.

Spirochætes occur in the crystalline style and digestive tract of many bivalve molluscs. The first molluscan spirochæte to be studied was that of the oyster, named by Certes (1882) “Trypanosoma” balbianii (fig. 53). Similar spirochætes, probably belonging to the same species, occur in various species of Tapes and in Pecten (the scallop). S. balbianii has rounded ends (fig. 53). Other spirochætes occur in freshwater mussels (Anodonta spp). S. anodontæ, studied by Keysselitz (1906) and by Fantham (1907), has pointed ends. Gross (1911) suggested the generic name Cristispira for molluscan spirochætes, because they possess a well-marked membrane or “crista,” which appears to be absent from S. plicatilis, according to Zuelzer’s researches.

Schaudinn in 1905 founded the genus Treponema for the parasite of syphilis (T. pallidum), discovered by him and by Hoffmann. According to Schaudinn the Treponemata have no membrane or crista. The pathogenic agent of yaws or frambœsia, discovered by Castellani, is also placed in the genus Treponema, as T. pertenue.

There remain the blood spirochætes. It is somewhat disputed as to whether these organisms possess a membrane. The present writer considers that they have a slight membrane or crista. The name of the genus in which to place the blood-inhabiting forms is somewhat uncertain and disputed. Various generic names given to them are Spirochæta, Treponema, Spiroschaudinnia (Sambon) and Borrelia (Swellengrebel). Included in this division are the causal agents of relapsing or recurrent fever. These Protists will be named, for description, Spirochætes without prejudice as to the ultimate correct generic name.

It is sometimes made a matter of argument as to whether the spirochætes are Protozoa or Bacteria. Such arguments are somewhat unprofitable. Morphologically the spirochætes are like the Bacteria in possessing a diffuse nucleus. They differ from Spirillum, an undoubted bacterial genus, in being flexible and not possessing flagella. Molluscan spirochætes, however, may appear to have flagella if their membrane becomes frayed or ruptured, when the myonemes therein (fig. 53), becoming separated, form apparent threads or flagella (Fantham, 1907–08).[142]

[142] Quart. Journ. Microsc. Sci., lii, p. 1.

Again, the mode of division of spirochætes has been used as a criterion of their bacterial or protozoal affinity. They have been stated to divide transversely, longitudinally, and by “incurvation,” or bending on themselves in the form of a *U*, “a form of transverse fission.” The present writer believes that they divide both transversely and longitudinally, and that there is a periodicity in their mode of division at first longitudinal (when there are few spirochætes in, say, the blood) and then transversely (when spirochætes are numerous in the blood).[143] Some authors consider that longitudinal division is explained by “incurvation.”

[143] Proc. Roy. Soc., B, lxxxi, p. 500.

The spirochætes of relapsing fever show a remarkable periodic increase and decrease in numbers in the blood. They are transmitted by ticks or by lice. They react to drugs (e.g., salvarsan or “606”) rather like trypanosomes, and--like Protozoa, but unlike Bacteria--they are cultivated with difficulty. These and other criteria have been used to endeavour to determine whether they are Protozoa or Bacteria. The present writer believes that they are intermediate in character, showing morphological affinities with the Bacteria and physiological and therapeutical affinities with the Protozoa. The group Spirochætacea, as an appendix to the Protozoa, has been created for them by the present writer (Jan., 1908). Others have placed them in the Spirochætoidea of the Bacteria or with the Spirillacea. Doflein (1909) called them Proflagellata. Further discussion is unnecessary, as they are undoubtedly Protista (see p. 29).

There is no true conjugation, sex or encystment in spirochætes, but morphological variation may occur.[144] They may agglomerate.

[144] Fantham, Parasitology, ii, p. 392.

The Spirochætes form an interesting chapter in the evolution of parasites. There are free living forms, parasitic forms in the guts of both vertebrates and invertebrates, and blood-inhabiting forms. These probably represent the order of evolution of parasitism. The blood-inhabiting forms are pathogenic to warm-blooded hosts.

We must now consider the blood Spirochætes and the Treponemata (organisms of syphilis and of yaws).

THE SPIROCHÆTES OF THE BLOOD.

There are at least two important human parasites included hereunder:--

(a) Spirochæta recurrentis (=S. obermeieri), (b) Spirochæta duttoni.

More is known of the life-cycle of Spirochæta duttoni, and it will be convenient to consider that first.

*Spirochæta duttoni*, Novy and Knapp, 1906.

The specific name duttoni was also given, independently, to this parasite in 1906 by Breinl and Kinghorn.

S. duttoni is the pathogenic agent of African tick fever in man, prevalent in the Congo State and other parts of Africa. The full-grown organism is about 16 µ to 24 µ long, and has pointed ends. It is 0·25 µ to 0·5 µ broad. P. H. Ross and Nabarro were among the earliest to see a spirochæte in the blood of patients in Uganda. It is transmitted by the tick, Ornithodorus moubata.

In the blood of the patient some of the spirochætes may show, after staining, lighter and darker portions (chromatin dots) and evidence of the possession of a very narrow membrane (fig. 54). The mode of division has already been discussed. Periodicity in the direction of division was first described by Fantham and Porter,[145] (1909). Just before the crisis in African tick fever, Breinl has stated that S. duttoni becomes thinner in the spleen and bone-marrow and rolls up into skein-like forms, which are surrounded by a thin “cyst” wall (probably the periplast). Such occur in apyrexial periods. Inside the cyst the spirochæte breaks up into granules. Balfour and Sambon have described somewhat similar rolled up forms, breaking into granules, inside the red blood cells of Sudanese fowls in the case of S. granulosa (possibly only a variety of S. gallinarum). The intracorpuscular stage is not definitely established.

[145] Proc. Roy. Soc., B, lxxxi, p. 500.

The granule phase, however, is an essential one in the invertebrate transmitter (fig. 54_c_). In 1905,[146] Dutton and Todd proved experimentally that O. moubata transmitted S. duttoni. They fed ticks, obtained from Congo native huts in which infected persons lived, on monkeys and the latter became infected. Dutton and Todd also found the offspring of infected ticks to be capable of transmitting the infection to experimental animals. They concluded that O. moubata was a true intermediate host.

[146] Liverpool Sch. Trop. Med., Memoir xvii; Lancet, Nov. 30, 1907, p. 1523.

A little later in 1905, Koch stated that spirochætes from the gut of the tick penetrated the gut wall and tissues and found their way into the eggs in the ovary. Koch figured tangled masses of spirochætes as occurring in the tick eggs. He found ticks infective to the third generation. He thought that the infection was spread by the salivary fluid of the tick, in the act of biting. (This is now known to be incorrect.) Markham Carter (1907) corroborated Koch’s work on the spirochætes in the tick eggs, and they have been seen since by Kleine and Eckard (1913).

Sir William Leishman,[147] in 1909–10, found that at ordinary temperatures the salivary glands of infected ticks (O. moubata) were not themselves infective, and that the infection occurred by way of the ticks’ excretion. The spirochætes (contained in the ticks’ excrement) found their way into the vertebrate host through the wound made by biting. While feeding, ticks pass large quantities of clear fluid from the coxal glands; in this fluid an anticoagulin occurs. Some of the ticks also pass thick, white Malpighian secretion, that is, excrement, towards the end of the feed. Leishman, using experimental monkeys, showed that if infected ticks were interrupted while feeding, then no infection resulted in the monkeys. If, however, the ticks were allowed to finish their feed, and the Malpighian secretions were passed, then the experimental monkeys became infected. Fantham[148] and Hindle[149] (1911), independently, have repeated the experiments with mice.

[147] Journ. Roy. Army Med. Corps, xii, p. 123; Lancet (1910), clxxviii, p. 11.

[148] Annals Trop. Med. and Parasitol., v, p. 479.

[149] Parasitology, iv, p. 133.

Leishman’s methods and results may be summarized thus: Saline emulsions of the organs of infected ticks were made, after the organs had been most carefully dissected out. The ticks were first kept for several days at certain constant temperatures, such as 24° to 25° C. or blood heat, 37° C. The saline emulsions of the organs were inoculated, separately, into experimental animals, and the results recorded:--

At 24° C. At 37° C. Salivary glands Negative Positive Malpighian tubules Positive Positive Gut and contents Positive Positive Excrement Positive Positive Genital organs Positive Positive

Coxal fluid is usually negative; thick, white excrement from Malpighian tubes is positive.

When the ticks were incubated at 21° to 24° C. no spirochætes, as such, were seen in the organs, except perhaps in the gut, where they often disappeared in a few days. When the ticks were previously incubated at 35° to 37° C. for two to three days, spirochætes, as such, reappear in the gut, organs and hæmocœlic fluid. The infection proceeds, not from the salivary gland, but from the infective excrement, that is, from the thick, white material voided by the tick while feeding, usually towards the end of the meal. This Malpighian excrement passes into the wound caused by the bite, being greatly aided by the clear and more limpid coxa fluid, which bathes the under surface of the tick’s body, and mixes with and carries the infective excrement into the wound. Ticks remain infective for a long time.

The spirochætes in the gut of infected ticks divide by a process of multiple transverse fission into granules, which are composed of chromatin (fig. 54). These granules--sometimes known as coccoid bodies--are capable of multiplication. Leishman first found them in clumps inside the cells of the Malpighian tubules (cf. fig. 55).

To summarize, when spirochætes are ingested by a tick, some of them pass through the gut-wall into the hæmocœlic (body) fluid. They then bore their way into the cells of various organs (fig. 55_a_) and break up into coccoid bodies. In this manner the granules find their way into the ovaries and ova, thus explaining how the young ticks are born infected. Inoculation of these chromatinic granules usually produces infection. Infective granules are also seen in the rudiments of the Malpighian tubules of embryo ticks. Bosanquet and Fantham (1911), independently, have shown that molluscan spirochætes also break up into similar granules or coccoid bodies. Gross has also demonstrated multiple transverse fission in molluscan forms. Marchoux and Couvy (1913) and Wolbach (1914) consider the granules or coccoid bodies to be degeneration products. This is unlikely (see below).

Schuberg and Manteufel have found that certain O. moubata, perhaps 30 per cent. of the specimens of a given neighbourhood, may acquire a natural active immunity against infection with S. duttoni.

S. duttoni, or a closely allied form (by some termed S. novyi), occurs in Colombia, and is spread by the tick Ornithodorus turicata. In Panama a similar spirochæte is probably spread by O. talaje.

*Spirochæta gallinarum*, Stephens and Christophers, 1905 (= *Spirochæta marchouxi*, Nuttall, 1905).

This Spirochæte, which occurs in fowls and is pathogenic, is transmitted by the tick Argas persicus. It is about 10 µ to 20 µ long. There is a pathogenic spirochæte known to occur in geese, named by Sakharoff (1891) S. anserina, and found in Caucasia. This may be the same as S. gallinarum, in which case the name S. anserina will have priority. These organisms cause fever, diarrhœa, anæmia and death. The life history of the avian pathogenic spirochætes has been studied by Balfour, by Hindle[150] and by Fantham.[151] It is essentially similar to that of S. duttoni.

[150] Parasitology, iv, p. 463.

[151] Annals Trop. Med. and Parasitol. (1911), v, p. 479.

Marchoux and Couvy[152] (1913) consider that the “fragmentation of the chromatin” in spirochætes is a process of degeneration. Working with A. persicus and S. gallinarum, they state that a large number of the spirochætes ingested by the Argas almost immediately pass through the wall of the alimentary canal and appear in the hæmocœlic fluid. Marchoux and Couvy consider that Leishman’s granules may be found in the Malpighian tubules of various Arachnids. They found spirochætes in the cephalic glands of infected Argas. They consider that spirochætes remain as wavy spirochætes within the tick, if they are to be infective, though the spirochætes may become so thin as to be invisible! The latter argument is obviously weak, and it was never asserted that all granules in the Malpighian tubules of infected ticks were derived from spirochætes. With dark-ground illumination small, refractile spirochætal granules may be seen to grow into spirochætes. The granule phase of spirochætes has recently been discussed by Fantham[153] (1914).

[152] Annales Inst. Pasteur, xxvii, pp. 450, 620.

[153] Annals Trop. Med. and Parasitol., viii, p. 471.

*Spirochæta recurrentis*, Lebert, 1874.

Syn.: Spirochæta obermeieri, Cohn, 1875.

This organism was discovered by Obermeier (1873) in cases of relapsing fever in Berlin. Short forms 7 µ to 9 µ long, and longer (probably adult) forms, 16 µ to 19 µ, are found in the blood. The width is 0·25 µ. Parasites 12 µ or 13 µ long are often observed.

The spirochæte is found in the blood during febrile attacks and relapses, but not during intervening periods. It can be inoculated into monkeys, rats and mice. It can live in the bed-bug, Cimex lectularius, and Nuttall has succeeded in transmitting S. recurrentis from mouse to mouse by the bites of the same bug. The French investigators Sergent and Foley (1908–9) in Algeria, and Nicolle, Blaizot and Conseil (1912) in Tunis, have shown experimentally that S. recurrentis (var. berbera) is transmitted by lice. The latter workers also demonstrated the method of infection that commonly occurs, namely, by the scratching of the skin and crushing of lice containing spirochætes on the excoriated surface of the body.

Lice as transmitting agents for relapsing fever were indicated by Mackie[154] in 1907. An epidemic among Indian school children furnished the materials.[155] It was noted that out of 170 boys, 137 were infected, and the boys were very verminous. Among the girls, 35 out of 114 suffered, and few lice were found on them. Twenty-four per cent. of the lice taken from the boys contained spirochætes as compared with 3 per cent. of those from the girls. As the epidemic died out among the boys, the lice also became fewer, and an increase in the number of cases among the girls coincided with an increase in the number of lice. Spirochætes were found in the gut, Malpighian tubules and genital organs of the lice. Mackie thought that infection of the patients was brought about by the regurgitation of the spirochætes when the lice fed, but proof of this was lacking.

[154] Brit. Med. Journ., Dec. 14, 1907, p. 1706.

[155] See also Nuttall, Herter Lecture on Spirochætosis, Parasitology, v, p. 269.

In 1912, Nicolle, Blaizot and Conseil,[156] working in Tunis and using chiefly an Algerian strain of relapsing fever spirochætes (sometimes called S. berbera), showed by direct experiments that infection by means of the bites of Pediculus vestimenti and P. capitis was untenable. As many as 4,707 infected lice were fed on one man, and 6,515 on another occasion were allowed to bite a man after they had fed on a monkey heavily infected with spirochætes, yet no infection of the man followed. Examination of the lice showed that the spirochætes left the gut soon after they were ingested, and passed into the body cavity, which swarmed with spirochætes. The contents of the alimentary tract and the fæces of the lice alike were uninfective. The spirochætes did not reappear in the gut till eight days after an infective feed, but some persisted as late as the nineteenth day when kept at 28° C.

[156] C.R. Acad. Sci., cliv, p. 1636; clv, p. 481.

It was noted that the irritation due to the lice caused scratching, and that thereby lice became crushed on to the skin. An emulsion was made of two infected lice and rubbed on to the slightly excoriated skin of one of the above workers. Infection followed five days later. A drop of emulsion placed on the conjunctiva of the human eye produced spirochætosis after an incubation of seven days. The body contents of such lice, then, produce infection when they reach the blood by any excoriated or penetrable surface. The stages leading up to infection in nature briefly are: The irritation due to the louse bites causes scratching, and the lice are crushed on to the skin. The slight abrasion is quite sufficient to permit the entry of the parasite. The louse bite alone is harmless. Infection by way of the eye is quite probable in Africa, remembering the constant trouble due to sand, dust, insects, etc., resulting in frequent touching of the eyes.

The spirochætes occur in the body fluid of the lice and can pass in it to the adjacent organs. Thus they probably find their way into the genital organs, and into the eggs of the lice. Eggs laid twenty to thirty days after the parent became infected have retained the infection, and the larvæ issuing from such eggs must have contained some form of spirochætes, for an emulsion of either the eggs or the larvæ produced spirochætosis when inoculated into monkeys. Further details regarding the spirochætosis in the eggs of the lice and in the larvæ are needed. Hereditary infection, however, has been demonstrated, but is not very common. Sergent and Foley (1914) state that the spirochæte possesses a very small and virulent form which it assumes during apyrexial periods in man and during a period following an infecting meal in the louse. Nicolle and Blanc (1914) find that the organisms are infective in the louse just before they reappear as spirochætes. Nicolle and Blaizot found that female lice were more susceptible to spirochætes than males, four times as many females as males being infected.

Tictin (1897) found S. recurrentis in bugs recently fed on patients, and infected a monkey with the fluids of crushed bugs. Karlinski (1902) found the spirochætes in bed-bugs in infected houses. There is some other evidence to show that bugs may transmit the spirochæte in Nature. Further researches are needed regarding the relationship of bed-bugs and human spirochætosis.

Multiplication of S. recurrentis is by longitudinal and transverse division (including so-called “incurvation”), and the organism forms small, ovoid bodies (“coccoid” bodies) in the same way as S. duttoni.

S. recurrentis is the cause of European relapsing fever, and a number of possible varieties of it are associated with relapsing fevers in other parts of the world. Such spirochætes only differ by biological reactions, such as acquired immunity tests. They include:--

S. rossii, the agent of East African relapsing fever; S. novyi, the agent of North American relapsing fever; S. carteri, the agent of Indian relapsing fever; S. berbera, the agent of North African and Egyptian relapsing fever.

OTHER HUMAN SPIROCHÆTES are:--

S. schaudinni. This organism, according to Prowazek, is the agent of ulcus tropicum. It varies in length from 10 µ to 20 µ.

S. aboriginalis has been found in cases of granuloma inguinale in British New Guinea and Western Australia. It also occurs in dogs, and may not be truly parasitic.

S. vincenti. This spirochæte is 12 µ to 25 µ in length, tapers at both ends and has few coils. It has been associated with angina vincenti. It often occurs in company with fusiform bacilli.

S. bronchialis, found by Castellani in 1907 in cases of bronchitis in Ceylon. The parasites are delicate, but show morphological variation. This organism is important and has since been found in the West Indies, India, Philippine Islands and various parts of Africa, such as the Anglo-Egyptian Sudan, Uganda and West Africa. It has recently been the subject of research by Chalmers and O’Farrell, Taylor, and Fantham.

S. phagedenis was found by Noguchi in a ten days old ulcerated swelling of the labium. The organism shows much variation in size, being 4 µ to 30 µ in length.

S. refringens (Schaudinn, 1905) occurs in association with Treponema pallidum in syphilitic lesions, but is non-pathogenic. It is 20 µ to 35 µ long and 0·5 µ to 0·75 µ broad, being larger than T. pallidum and more easily stained.

Various spirochætes have also been notified in vomits, chiefly in Australia; others from the human intestinal tract, e.g., S. eurygyrata; S. stenogyrata (Werner); S. hachaizæ (Kowalski), in cholera motions; S. buccalis (Cohn, 1875) and S. dentium occurring in the human mouth and in carious teeth (S. dentium, Koch, 1877, being the smaller); S. acuminata and S. obtusa found by Castellani in open sores in cases of yaws.

Animal spirochætes of economic importance include:--

S. anserina, highly pathogenic to geese.

S. gallinarum (= S. marchouxi) in fowls. (See p. 119.)

S. theileri in cattle and S. ovina in sheep also occur in Africa; their pathogenicity is not clear.

S. laverani (= S. muris), occurring in the blood of and pathogenic to mice, is probably the smallest spirochæte from the blood, being only 3 µ to 6 µ long.

Numerous spirochætes have been recorded from the guts of various mammals, birds, fishes, amphibia and insects.

CULTIVATION OF SPIROCHÆTES.--Cultures of spirochætes have been made with little success or with great difficulty until comparatively recently, when Noguchi (1912) devised a means whereby he has cultivated most of the pathogenic spirochætes as well as some Treponemata.

Noguchi has now cultivated S. duttoni, S. recurrentis, S. rossii, S. novyi and S. gallinarum from the blood; S. phagedenis[157] from human phagedænic lesions; S. refringens[158] and spirochætes from the teeth.

[157] Journ. Exptl. Med., xvi, p. 261.

[158] Journ. Exptl. Med., xv, p. 466.

His method is as follows:--

A piece of fresh, sterile tissue, usually rabbit kidney, is placed in a sterile test-tube. A few drops of citrated blood from the heart of an infected animal, e.g., rat or mouse, is added, and about 15 c.c. of sterile ascitic or hydrocœle fluid is poured quickly into the tube. Some of the tubes are covered with a layer of sterile paraffin oil, others are left uncovered. The tubes are incubated at 37° C. The best results are obtained if the blood is taken from an animal forty-eight to seventy-two hours after it has been inoculated, that is, before the spirochætes reach their maximum multiplicative period in the blood. The presence of some oxygen seems indispensable for these blood spirochætes, and they fail to develop in vacuo or in an atmosphere of hydrogen.

For subcultures, 0·5 c.c. of a culture is added to the medium instead of citrated blood, and it is useful to add a little fresh, normal blood, either human or from an animal, such as a rat.

Noguchi found that the events in cultures were:--

S. duttoni,[159] maximum multiplication on the eighth to ninth day; disintegration beginning on the tenth day, spirochætes disappeared after about the fifteenth day. No diminution of virulence was found at the ninth day.

[159] Journ. Exptl. Med., xvi, p. 202.

S. rossii (= S. kochi).[160] Maximum development on the ninth day, after which the virulence diminishes. The incubation period is also prolonged.

[160] Ibid., p. 205.

S. recurrentis[161] (= S. obermeieri). Maximum growth on the seventh day.

[161] Ibid., p. 205.

S. novyi.[162]--Maximum development on the seventh day. It is more difficult to grow than the preceding forms.

[162] Ibid., p. 208.

All the above spirochætes showed undoubted longitudinal division and transverse division was observed in part.

S. gallinarum[163] can be cultivated as above, but transverse division was usual here. Maximum growth occurred in the culture about the fifth day.

[163] Ibid., p. 620.

TREPONEMATA.

The genus Treponema (Schaudinn, 1905), includes minute, thread-like organisms, with spirally coiled bodies, the spirals being preformed or fixed. No membrane or crista is present, according to Schaudinn, though a slight one is said by Blanchard to be present in the organism of yaws. The ends of the organisms are tapering and pointed. Multiplication is by longitudinal and transverse division. The most important members of the genus are T. pallidum, the agent of syphilis, and T. pertenue, which is responsible for frambœsia or yaws.

*Treponema pallidum*, Schaudinn, 1905.

Syn.: Spirochæta pallida.

Treponema pallidum was first described by Schaudinn and Hoffmann in 1905 under the name of Spirochæta pallida. It has also been described under the names of Spironema pallida, Microspironema pallida and Trypanosoma luis. Siegel in 1905 described an organism which he called Cytorhyctes luis and considered to be the agent of syphilis. Schaudinn reinvestigated Siegel’s work and found T. pallidum, which he considered to be the causal agent of the disease, and pronounced against Cytorhyctes luis. It is probable now that both workers were correct, for Balfour (1911) has seen the emission of minute granules or “coccoid” bodies from T. pallidum and these granules probably correspond to the C. luis of Siegel. Recently E. H. Ross, having observed a spirochæte stage in the development of Kurloff bodies, thinks that T. pallidum is a stage in the life-history of a Lymphocytozoon. MacDonagh has also described a complicated and somewhat similar cycle, but these observations require further study and confirmation.

T. pallidum varies from 4 µ to 10 µ in length, its average length being 7 µ, while its width is usually about 0·25 µ. Longer individuals of 16 µ to 20 µ have been recorded. The body has from eight to ten spiral turns and forms a tapering process at each end (fig. 56). The organism is most difficult to stain, and its internal structure is little known. It is possibly like that of Spirochæta duttoni or S. balbianii, as the “granule shedding” observed by Balfour is strongly suggestive of the formation of resistant bodies by those spirochætes. Hoffmann (1912) has seen the formation of spores in T. pallidum.

The Treponemata occur in the primary and secondary sores, but are difficult to find in the tertiary eruptions of syphilis. Noguchi and Moore (1913) and Mott[164] (1913) have demonstrated T. pallidum in the brain in cases of general paralysis of the insane. Marie and Levaditi (1914), however, consider that the treponeme found in the brain in such cases is different from T. pallidum.

[164] Brit. Med. Journ., Nov. 15, 1913. p. 1, 271.

CULTIVATION of T. pallidum.--This has been accomplished successfully by Noguchi,[165] using a modification of his method for spirochæte cultivation, for T. pallidum is much more difficult to grow than spirochætes, being a strict anaerobe.

[165] Journ. Exptl. Med., xv, p. 90; xvi, p. 211.

The apparatus consists of two glass tubes, the upper being connected to the lower by a narrower tube passing through a rubber cork (fig. 57). Both tubes are carefully sterilized.

A piece of fresh, sterile rabbit’s kidney is placed in the lower tube, which is filled with ascitic fluid, or ascitic fluid and bouillon mixture. The tube is inoculated with syphilitic material and corked by inserting the upper tube. In the bottom of the upper tube a piece of sterile rabbit’s kidney is placed and syphilitic material poured over it. A mixture of one part ascitic fluid and two parts of slightly alkaline agar is then poured over the tissue and allowed to solidify. When solid, a layer of sterile paraffin oil is poured on top of it, and the top plugged with cotton wool (fig. 57). The whole is then incubated at 37° C. for two or three weeks. The tissue removes traces of oxygen from the lower levels of the medium and also probably provides a special form of nourishment. At first T. pallidum grows in the solid medium, and then when the cultural conditions in the lower fluid portion become favourable, the organisms migrate thither and multiply abundantly. At first the culture is impure, but after several transferences a pure culture is obtained readily.

The syphilitic material for culture is prepared by cutting off pieces of tissue from the lesions, washing in sterile salt solution containing 1 per cent. sodium citrate, and then emulsifying the tissue in a mortar with sodium citrate.

Good cultures show rapid multiplication, which is invariably by longitudinal division.

In his various cultivation experiments Noguchi[166] found morphological and pathogenic variations in T. pallidum. Three forms of the organism were found, namely, thicker, average and thinner types. The lesions caused in the testicle of the rabbit differ according to the variety inoculated, but more work is necessary on the subject.

[166] Journ. Exptl. Med., xv, p. 201.

Noguchi[167] has cultivated a separate organism, T. calligyrum, from the surface of human genital or anal lesions, either syphilitic or non-syphilitic. It is apparently non-pathogenic, and is 6 µ to 14 µ long.

[167] Journ. Exptl. Med., xvii, p. 89.

Hata (1913)[168] has modified the Noguchi technique for the cultivation of spirochætes and treponemes, with a view to simplification and convenience. Hata substitutes normal horse serum for ascitic fluid and the “buffy coat” of the clot of horse blood in place of the small pieces of rabbit’s kidney. It is unnecessary to place sterile paraffin on the surface of the medium.

[168] Centralbl. f. Bakt., Orig., lxxii, p. 107.

The horse serum is mixed with twice its volume of physiological saline solution. The mixture is placed in tubes which are heated on a water-bath at 58° C., the temperature being raised gradually until it reaches 70° or 71° C. in three hours. The tubes are then heated at 71° C. for half an hour. After cooling, the contents will consist of an opaque semi-coagulated mass. This semi-coagulated serum and saline mixture may be substituted for Noguchi’s ascitic fluid.

The buff coagulum is cut into small pieces, about 1 c.c. in volume. They must be forced with a sterile glass rod to the bottom of the semi-coagulated serum and saline mixture. The medium is inoculated with a small quantity of infected blood and kept at 37° C. In the case of S. recurrentis, growth of spirochætes is observed on the second day, reaching a maximum in five to seven days. The growth of the organisms proceeds rather more slowly, they live for a longer period and maintain their virulence better than in Noguchi’s medium.

*Treponema pertenue*, Castellani, 1905.

Syn.: Spirochæta pertenuis; S. pallidula, Castellani, 1905.

Castellani discovered the organism in 1905, in scrapings of yaws pustules. He first described it under the name of Spirochæta pertenuis.

Treponema pertenue (fig. 58), though delicate and slender, shows great morphological variation both in length and thickness. It may be short, e.g., 7 µ, but can attain 18 µ to 20 µ in length and may be even larger. In cultures made by Noguchi, thick, medium and thin forms were found, each giving rise to a different type of frambœsial lesion when inoculated into the testicles of rabbits, thus suggesting the possibility of the occurrence of varieties of T. pertenue.

The organism is difficult to stain, but occasionally deeper staining granules are found along its body. They may represent a diffuse nucleus. Granule formation similar to that of T. pallidum has been observed by Ranken, using dark-ground illumination.

Many experiments have been made with a view to establishing the identity of the organism of yaws and also of differentiating between the causative agents of yaws and syphilis. Both monkeys and the human subject have been experimentally inoculated with yaws material and have developed the disease.

In an early experiment, negroes were inoculated with the secretion from lesions of yaws. All of them developed the disease, nodules appearing, chiefly at the seat of inoculation, in from twelve to twenty days, followed by the usual eruption. Similar results were obtained with thirty-two Chinese prisoners, who were inoculated with yaws, twenty-eight becoming infected.

A naturally infected yaws patient when inoculated with syphilis, contracted that infection, thus showing that yaws does not confer immunity to syphilis. This has also been observed naturally, when yaws patients have contracted syphilis.

Experiments with monkeys have been successfully performed. The incubation period varies from sixteen to ninety-two days. Lesions appear first at the seat of inoculation, and in some monkeys the eruption is localized to this spot, though the infection is general, T. pertenue occurring in the spleen, lymphatics, etc. Monkeys inoculated with splenic blood of a yaws patient, and also sometimes with blood from the general circulation, have become infected.

Castellani and others have shown that monkeys successfully inoculated with syphilis do not become immune to yaws, and vice-versâ.

Craig and Ashburn, using the monkey Cynomolgus philippinensis, found these animals susceptible to yaws but not to syphilis.

The ulcerated lesions of frambœsia are rapidly invaded by numerous bacteria as well as by different spirochætes, of which Castellani has described three distinct species. One is identical with Spirochæta refringens, Schaudinn, the other two are thin and delicate. One, S. obtusa, has blunt ends; the other S. acuminata, has pointed ends. T. pertenue is also present.

The reasons for considering T. pertenue to be the specific cause of frambœsia are:--

(1) T. pertenue is the only organism present in non-ulcerated papules, in the spleen and in the lymphatics of yaws patients, or of monkeys artificially infected with the disease. By no method has any other organism been obtained.

(2) Extract of frambœsia material, free from all organisms other than T. pertenue, reproduces the disease if inoculated.

(3) Extract of frambœsia material deprived by filtration of T. pertenue is no longer infective on inoculation.

The method of infection is contaminative, by direct contact. Women in Ceylon are frequently infected by their children. Any slight skin abrasion is sufficient to admit the parasite. In some cases, insects may carry the disease from person to person, and even in hospitals, when dressings are removed, it has been noticed that flies greedily suck the secretion from the ulcers. T. pertenue has been recovered from flies that have fed on yaws, and monkeys have contracted the disease when flies were placed and retained on them for a short time, after the insects had fed on yaws material.

CULTIVATION.--T. pertenue has been cultivated by Noguchi, who finds three types of parasites in his cultures, as before mentioned. Its multiplication is by longitudinal division.

Noguchi[169] (1912), has cultivated species of Treponema from the human mouth, e.g., T. macrodentium, T. microdentium and T. mucosum, the latter from pyorrhea alveolaris. These parasites in the past may have been confused under the name Spirochæta dentium.

[169] Journ. Exptl. Med., xv, p. 81; xvi, p. 194.

Class III. *SPOROZOA*, Leuckart, 1879.

The third group of the Protozoa consists entirely of parasitic organisms forming the class known as the Sporozoa or spore-producing animals. The members of this class are characterized by possessing very great powers of multiplication, coupled with a capacity for producing forms that serve for the transference of the organisms to other hosts. These reproductive bodies, whether for increase of numbers within one host or for transmission to another host, are called spores. But, strictly, the term spore should be used only in the latter connection, when a protective or resistant coat known as a sporocyst envelops the body of the spore.

The Sporozoa are widely distributed, occurring in various tissues and organs of Annelids, Molluscs, Arthropods, and Vertebrates. Their food, which is fluid, is absorbed osmotically. The life-cycle of a Sporozoön may be completed within one host or may be distributed between two different hosts.

The Sporozoa were divided by Schaudinn into two groups or sub-classes, called (1) the *Telosporidia*, and (2) the *Neosporidia*.

The Telosporidia are Sporozoa in which the reproductive phase of the parasites is distinct from the growing or trophic phase, and follows after it. The Neosporidia include Sporozoa in which growth and spore-formation go on simultaneously. This classification is not final, for certain exceptions and difficulties are already known with regard to it. It is possible that the class Sporozoa is not a natural entity, but should be replaced by two classes of equal rank, corresponding in most respects with the Telosporidia and Neosporidia.

The *Telosporidia* comprise the *Gregarinida*, the *Coccidiidea*, and the *Hæmosporidia*. Doflein combines the two latter orders into one known as the *Coccidiomorpha*.

The *Neosporidia* comprise the *Myxosporidia*, the *Microsporidia*, the *Actinomyxidia*, the *Sarcosporidia*, and the *Haplosporidia*. Doflein combines the first three orders into one, the *Cnidosporidia*.

Sub-Class. TELOSPORIDIA, Schaudinn.

Sporozoa in which the reproductive phases follow completion of growth.

Order. *Gregarinida*, Aimé Schneider emend. Doflein.

Knowledge of the Gregarinida probably goes back as far as the year 1684, when Redi observed gregarines in the crab, Cancer pagurus. Von Cavolini (1787) found them in Cancer depressus. The name Gregarina was created by L. Dufour (1828), who observed masses of these organisms in the gut of insects of different orders. Hammerschmidt (1838) and von Siebold found rich infestations in insects, while Dujardin (1835) and Henle described various genera from segmented worms. Henle (1835) also observed cysts containing “navicellæ” in the sperm-sacs of segmented worms, and attention was drawn to his researches by the discovery by von Siebold (1839) of “pseudonavicellæ” in the gut of Sciara nitidicollis. Up to this time many workers considered the gregarines to be worms, but Kölliker (1845) investigated many of them and maintained their unicellular nature, while Stein’s work (1848) showed the interrelation of the pseudonavicellæ and the gregarines. The discovery of amœboid germs in the pseudonavicellæ by Lieberkühn (1855) and the demonstration of myonemes further aided in the elucidation of their true systematic position. The entire process of conjugation, of which Dufour had seen one phase, was followed by Giard under the microscope.

From 1873 onwards Aimé Schneider made important additions to the knowledge of the morphology, life-history, and systematic position of numerous gregarines. Bütschli (1881) and L. Léger (1892) also contributed much work on the subject. The discoveries of Schaudinn with regard to the life-cycle of Coccidia gave a fresh stimulus to the study of the Gregarines, whereby the life-cycles of numerous forms and the phases thereof have been elucidated.

Asexual multiplication is not common among the Gregarines, but is known to occur in the sub-order Schizogregarinea, formerly known as the Amœbosporidia.

Although the Gregarinida are not known to be parasitic in man or other vertebrates, they are of great interest, inasmuch as they are among the earliest known Sporozoa, and therefore will be briefly described here.

The Gregarines are usually elongate, somewhat flattened organisms (figs. 59, 60), whose bodies are enclosed in an elastic and often thick cuticle. The enclosed living substance shows a separation into ectoplasm and endoplasm, as is common among Protozoa. The cuticle is sometimes regarded as the outer portion or epicyte of the ectoplasm. A single, vesicular, spherical, or elliptical, large nucleus, with its chromatin concentrated to form a spherical karyosome, is present. The body of some gregarines may be divided by ingrowing ectoplasmic partitions or septa, and are then said to be “septate” or “polycystid” (fig. 61). Other gregarines remain simple and non-septate, and are termed “monocystid” (fig. 59). The monocystid gregarines occur especially in the body cavity of Chætopoda and Insecta, more rarely in Echinodermata, in the parenchyma of Platyhelminthes, also in the gut of Tunicata and Insecta (fig. 60) and in the seminal vesicles of Annelida. In the polycystid gregarines a single septum only is present as a rule, and thus the body presents two portions: (1) an anterior portion termed the protomerite; (2) a posterior, larger portion, known as the deutomerite, which generally contains the nucleus. The protomerite is often modified anteriorly to form an organ of attachment, termed the epimerite (fig. 61), which is developed from the pointed rostrum of the sporozoite or primary infecting young gregarine. The structure of the epimerite may be complicated, being provided with hooks, spines, knobs, and other appendages. An extension of the polycystid condition is seen in Tæniocystis mira Léger (from the dipteran larva, Ceratopogon solstitialis), whose body shows a number of partitions, giving the organism a superficial resemblance to a tapeworm.

The ectoplasm of a gregarine exhibits three layers: (1) An epicyte (cuticle) externally of which the epimerite is composed; (2) a sarcocyte which forms the septa if present; (3) the deeper myocyte layer containing contractile elements in the form of fibrils or threads termed myonemes (fig. 62).

The endoplasm is fluid and granular, containing many enclosures, which are of the nature of reserve food materials. They consist of fat droplets or of paraglycogen, and give the organisms an opaque appearance. Lithocystis contains crystals of calcium oxalate in its endoplasm.

Many gregarines are capable of active movements, though they do not possess obvious locomotor organs. The movement is of a smooth, gliding character and two suggestions have been put forward to explain it. According to Schewiakoff, a gelatinous substance is secreted between the layers of the ectoplasm. This is extruded posteriorly and thus the animal is pushed forward. On the other hand, Crawley considers that the movements are produced by contractions of the myonemes. These two explanations are probably correct as far as each goes, and are to be regarded as supplementary to one another.

Occasionally, temporary associations of gregarines are formed by a number of individuals adhering to one another end to end. Such temporary associations are examples of syzygy. Such syzygies must not be confused with true associations which form an essential part of the life-cycle.

The life-cycle of a relatively simple gregarine, such as Monocystis agilis (fig. 59), parasitic in earthworms, may now be considered. The gregarines, being members of the Sporozoa, produce spores at one phase of the life-cycle. Each gregarine spore (fig. 63) develops within itself a number of minute, sickle-shaped or vermicular bodies, known as sporozoites or primary infecting germs. Eight sporozoites are often formed within each spore. When absorbed by a new host, the spore softens and the sporozoites issue from it. They are capable of active movement and may or may not enter a cell, such as one of those of the digestive tract, or, as in Monocystis, a cell lining the vesicula seminalis which becomes a sperm-cell aggregate (sperm morula). When the sporozoite has reached the place of its choice in the host it ceases active movements and proceeds to feed passively on the fluid substances around it, whether they be those of tissues or body fluids. This passive, growing and feeding form is known as the trophozoite. After a trophic existence of longer or shorter duration, the trophozoite ceases to feed and prepares for reproduction. Two trophozoites associate together, each of them first becoming somewhat rounded. The two trophozoites, now known as sporonts or gametocytes, become invested in a single common envelope or cyst (fig. 64, a). The nucleus of each gametocyte then divides by a series of binary fissions (fig. 64, b), and the daughter nuclei thus produced arrange themselves at the periphery of the parent cells (fig. 64, c). Cytoplasm collects around each of these nuclei, and thus a number of gametes are formed within each gametocyte. The gametes for a time exhibit active movements, and ultimately ripe gametes of different parentage fuse in pairs, that is, conjugation occurs (fig. 64, d). In this way zygotes are produced, the nucleus of each zygote being formed by the fusion of two gamete nuclei.

The zygote grows slightly and becomes oval or elongate, and at this period is often called the sporoblast. It then secretes an external membrane, the sporocyst. Nuclear division occurs inside the sporocyst by a series of three binary fissions (fig. 64, e), so that each sporocyst, now usually referred to as a spore, contains eight nuclei. The cytoplasm collects around each nucleus and eight vermicular sporozoites are produced within each spore (fig. 64, f), thus completing the life-cycle.

It will be noticed that in the above life-cycle no asexual multiplication occurs. These organisms, such as Monocystis, are known as the Eugregarines, and include the majority of the gregarines. The remainder, which have introduced schizogony into their life-cycle, are known as the Schizogregarines.

There are variations in the morphology and life-cycle of gregarines besides those that have been mentioned. It is not within the scope of this book to discuss them in detail, but the following may be noted:--

Morphological differentiation of gametes may occur as in Stylorhynchus oblongatus (fig. 65), which differentiation is probably of a sexual nature.

The sporocyst really consists of two layers, an epispore and an endospore. Externally the spores of different gregarines show great variety in shape and markings, and spines, or long processes may be present (fig. 66).

The resistant spores serve for the transmission of the gregarines from host to host. The mode of infection is contaminative, the spores expelled with the dejecta of one host being absorbed with the food of a new host.

The Gregarinida may be classified as follows:--

Sub-order I.--*Eugregarinea*, without schizogony.

Tribe 1.--Acephalina.--Without an epimerite and non-septate; often “cœlomic” (body-cavity) parasites. E.g.: Monocystis, with several species parasitic in the seminal vesicles of earthworms. Many other genera parasitic in Echinodermata, Tunicata, Arthropoda, etc.

Tribe 2.--Cephalina.--With an epimerite, either temporarily or permanently, in the trophic phase. Usually septate (except Doliocystidæ). Many families, genera and species. Common in the digestive tracts of insects. E.g.: Gregarina, with several species, Gregarina ovata in the earwig, Gregarina blattarum in the cockroach, Stylorhynchus in beetles, Pterocephalus in centipedes, etc.

Sub-order II.--*Schizogregarinea*, with schizogony.

Tribe 1.--Endoschiza.[170]--With schizogony occurring in the intracellular phase, e.g., Selenidium (from Annelida and Gephyrea), Merogregarina (from an Ascidian).

[170] See Fantham (1908), Parasitology, i, p. 369.

Tribe 2.--Ectoschiza.--In which the schizont is free, and schizogony is extracellular, e.g., Ophryocystis (from Blaps, a beetle), and Schizocystis (from Ceratopogon larva).

Order. *Coccidiidea*.

Hake (1839) first saw the organisms now termed Coccidia during his investigations on the so-called coccidial nodules of rabbits. The opinions as to the nature of these peculiar formations were very diverse. The discoverer considered them to be a sort of pus corpuscle; Nasse (1843) took them for epithelial cells of the biliary passages, others for helminthes, especially the ova of trematodes (Dujardin, Küchenmeister, Gubler, etc). Remak (1845) was the first to draw attention to their relation to the Psorospermia (Myxosporidia), and this investigator found them also in the small intestine and vermiform appendix of rabbits. Lieberkühn (1854), who examined not only the coccidia of rabbits, but found similar forms in the kidneys of frogs, likewise called them definitely psorosperms. To differentiate Müller’s psorosperms, which are found in fishes, from those of rabbits, etc., the latter were called egg-shaped psorosperms (Eimer), until R. Leuckart (1879) named them Coccidia and placed them in a group of the Sporozoa analogous to that of the Gregarinida, Myxosporidia, etc. Numerous works confirmed the occurrence of coccidia, not only in all classes of vertebrate animals, but also in invertebrates (Mollusca, Myriapoda, Annelida, etc.). A large number of genera and species have in the course of time been described which inhabit the epithelium of the intestine and its appendages for choice, but are also found in other organs (kidneys, spleen, ovaries, vas deferens, testicles). Some also live in the connective tissue of various organs, more particularly of the intestine.

The knowledge of the development of the coccidia was of particular importance in determining their classification. By means of encysted coccidia from the liver of rabbits, Kauffmann (1847) first confirmed the fact that the cyst, which was partly or entirely filled with granular contents, divided into three or four pale bodies (fig. 71) after a long sojourn in water. Lieberkühn observed the same process in the host in the case of the coccidia of the kidney of the frog. Stieda (1865) studied more minutely the changes that occur within the encysted coccidia of the liver of rabbits after the death of the host. He discovered that the bodies now known as “spores” were oval formations pointed at one pole, and surrounded by a delicate membrane, which exhibited a certain thickness at the pointed extremity and enclosed a slightly bent rodlet, expanding at either end into a strongly light-refracting globule; a finely granular globule was present in the middle of the spore. Waldenburg (1862) saw the same phenomenon in coccidia from the epithelium of the villi and Lieberkühn’s glands of the intestine of the rabbit; but the process in this case took place in a much shorter time.

According to the discovery of Kloss (1855), the spores of the coccidia of the urinary organ of the garden snail were formed in far greater numbers: the round spores also harboured several (five to six) rodlets, which after the bursting of the spore-envelope became free. Eimer’s researches (1870) afforded information regarding a Coccidium from the intestine of the mouse, which was transformed in toto into a “spore,” containing small sickle-shaped bodies. The fact was, moreover, established that the little bodies left the delicate envelope when in the intestine, made movements of flexion and extension, and were finally transformed into amœboid organisms, which apparently penetrated the epithelial cells; at all events, similar bodies of various sizes were seen in these cells. Taking the immense number of these parasites into account and the lack of any other cause, Eimer attributed the sudden death of his mice to the Gregarina falciformis, as the parasite was then called, just in the same way as a few years previously Reincke ascribed the acute and fatal intestinal catarrh of rabbits to the invasion of intestinal coccidia.

All that had become known about coccidia up to 1879 was then compiled by Leuckart, and completed by his own observations on the coccidia of the liver of the rabbit. Experimental infections had already been conducted by Waldenburg (1862) with intestinal coccidia of rabbits, and by Rivolta (1869–73) with the coccidia of fowls, which experiments confirmed the importance of the spores, or bodies enclosed in them, in the transmission of the parasites to other animals. Accordingly, it was assumed that after the entry of the spores into the intestine the sporozoites were set free, actively penetrated into the intestinal cells, where they grew into coccidia, and finally became encysted. The further development, i.e., the formation of spores, took place outside the host’s body in these cases; in other cases (Kloss, Eimer) it took place within the host. Although much regarding the cycle of development was still hypothetical, the ideas coincided with the observations, and were therefore universally regarded as established. Further research confirmed this view in numerous new forms.

L. Pfeiffer’s statements (1891) on the part that certain coccidia or their sporozoites played, or seemed to play, as causes of disease gave a renewed impetus to the investigation of the coccidia. The ingestion of even very numerous spores did not appear to account for the mass infection so frequently observed, even after Balbiani had confirmed the fact that there were two, and not one, sporozoites contained in every spore of the coccidia of rabbits (fig. 72). The hypothesis was therefore advanced that the sporozoites or young coccidia were able to divide once again by sporulating. The question was finally solved quite differently. R. Pfeiffer (1892) first confirmed the fact that in addition to the well-known method of sporulation in the coccidia of the rabbit that causes the infection of fresh hosts (“exogenous sporulation”), an enormous increase may follow in the already infected host in a manner that Eimer first observed in the coccidia of the intestine of the mouse (“endogenous sporulation”). It had hitherto been believed that some of the species of coccidia increased like the rabbit parasite, then known as Coccidium oviforme, and others like Eimeria falciformis, and this difference had been made the foundation of a classification. R. Pfeiffer was successful in observing the occurrence of both kinds of development in the same species, and expressed the opinion that endogenous sporulation (fig. 73), which takes place within the host, was the cause of the mass-infection that is mostly accompanied by serious consequences (fig. 74). L. Pfeiffer sought, especially, to demonstrate the correctness of this view as regards other species of coccidia and for this purpose he utilized the experiences already published. Coccidia were known to exist in a number of different hosts, and to propagate in some according to the Coccidium type, in others according to the Eimeria type. It therefore was reasoned that in this case it was not a question of two species belonging to different genera living side by side, with a different mode of development, but of one species, in the life of which both forms of development occurred alternately.

This interpretation of facts was combated especially by A. Schneider (1892) and by Labbé, but has, nevertheless, proved true, apart from the circumstance that Schuberg succeeded in discovering the hitherto unknown Coccidium form in the intestine of the mouse; and that, moreover, Léger confirmed the fact that there are no Arthropoda in which Eimeria are not found together with coccidia. The question was finally settled by experiments made by Léger with the coccidia of Scolopendra cingulata, by Schaudinn and Siedlecki with those of Lithobius forficatus, and by Simond with the coccidia of the rabbit. On Simond’s suggestion the sickle-shaped germs corresponding to the sporozoites, which are formed by endogenous sporulation, are generally termed merozoites; and in accordance with Schaudinn’s suggestion, those individuals which form merozoites are termed schizonts, and those which produce spores are called sporonts. In contradistinction to sporogony (exogenous sporulation), the term schizogony (endogenous sporulation) is used.

The more minute examination of these processes at last led to the discovery of sexual dimorphism, of copulation and of alternation of generations in the coccidia. Schuberg was the first to consider the possibility of copulation in coccidia; in addition to the formations which now are termed merozoites, he observed very diminutive bodies (“microsporozoites”) in the coccidia of the intestine of the mouse, which were able eventually to copulate. Labbé confirmed this observation in some of the species, and Simond expressed the opinion that bodies termed “chromatozoites” occurred in all coccidia. Copulation itself was then observed by Schaudinn and Siedlecki (1897). The copulating bodies were termed gametes. As, however, they differed considerably one from the other, the males were called microgametes (i.e., the microsporozoites of Labbé and the chromatozoites of Simond) and the females macrogametes. After copulation was completed sporogony took place, and in the cycle of development of one species this regularly alternated with schizogony (asexual multiplication). Schaudinn in 1900 described in detail the life-cycle of Eimeria (Coccidium) schubergi.

The recognition of this unsuspected complicated process was bound to effect reforms in the classification of the coccidia; and all the forms that had been regarded as developmental stages (Eimeria, etc.) had to be reconsidered.

Occurrence.--The Coccidiidea in their mature condition usually live within the epithelial cells of various organs, and by choice inhabit those of the intestine and of its associated organs. They also occur frequently in the excretory organs of mammals, birds, amphibia, molluscs, arthropods, and may also be found in the testes and vas deferens, but the statement that they live in hen’s eggs, as well as in the oviducts of fowls, has not been confirmed.[171] Some species inhabit the nuclei of cells, others live in the connective tissue, but their presence in the latter situation is probably only secondary, that is, they have only reached it from the epithelium of the affected organs.

[171] Notwithstanding the progress made during the last decades, the ova of helminthes and more particularly of trematodes, have been mistaken for Coccidia. Thus Poschinger (Zool. Anz., 1819, ix, p. 471) and Gebhard (Virchow’s Arch., 1897, No. 147, p. 536) mistook the ova of Distoma turgidum, Brds., for Coccidia. Podwyssotzki (Centralbl. f. allg. Path., 1890, i, p. 135) made a similar error with the ova (and vitelline sacs) of a species of Prosthogonimus (Distoma ovatum of the authors); von Willach (Arch. f. wiss. u. prakt. Thierheilk., 1892, xviii, p. 242) mistook the ova of a nematode for Coccidia.

The size of the Coccidiidea, corresponding as a rule to the capacity of their habitat, is usually small, but there are said to be species that attain a diameter of 1 mm. Their form[172] is globular, oval, or elliptical. External appendages are lacking, at least during the trophic or vegetative period of their life, which is spent in epithelial cells, within which they increase in size. Frequently one only is present in each cell, but more can occur. The body substance is composed of a more or less finely granular or distinctly alveolar protoplasm which exhibits no differentiation into ecto- and endoplasm. All species possess a nucleus that enlarges with their growth; sometimes it only shows through the cytoplasm as a lighter spot, or may even be quite concealed. It is vesicular, and besides containing very delicate threads of chromatin in the clear nucleoplasm, it contains generally only one large karyosome.

[172] The life-cycle given here is based on that of Eimeria (Coccidium) schubergi, after Schaudinn (1900). See “Untersuchungen über den Generationswechsel bei Coccidien,” Zool. Jahrb., Abt. f. Anat., xiii, pp. 197–292, 4 plates.

The infected epithelial cells degenerate sooner or later as the parasite feeds on them (fig. 67, II-IV). After their form has been changed by the action of the growing parasite, they finally perish. The cell membrane then alone surrounds the coccidia, which, at least in the species sufficiently known, begin to propagate by an asexual process (schizogony), the parasites themselves becoming schizonts, as the initial stage is usually called. They differ from later stages (sporonts or gametocytes), which resemble them in form, by the absence of granulations in the cytoplasm, as well as by the vesicular nucleus. The form is not always the same, for in some cases, at least, many schizonts assume a globular form.

Schizogony (fig. 67, V-VII) commences with a division of the nucleus, which takes place in different ways in the various species. This finally leads to the formation of numerous daughter nuclei which become smaller and smaller, and which collect beneath the surface of the schizonts. In some species the daughter nuclei collect only in one half of the schizont. A part of the protoplasm of the periphery now divides around each daughter nucleus, the remaining part (residual body) being left in the centre or on one side. The segments of the divided cytoplasm, each containing a nucleus, assume a fusiform shape and become merozoites, which very soon become free (fig. 67, VIII) and leave the residual body. They are distinguishable from the very similar sporozoites (fig. 67, I), as the merozoites possess a karyosome.

The merozoites move in a manner similar to that of the sporozoites. The movements consist either of slow incurvations with subsequent straightenings, or annular contractions along the entire extent of the body. In addition, there are gliding movements similar to those of many gregarines, and brought about in a like manner by the secretion at the posterior extremity of a gelatinous substance that hardens rapidly.

The merozoites do not gain the open in the usual way, but are destined to infect still further the same host by actively penetrating into other epithelial cells of the affected organ. Here they continue their growth and may again and again undergo schizogony. In the Infusoria the repeated segmentations finally cease and are renewed only after a conjugation. This is likewise the case with the Coccidia, with the difference that in the latter the two conjugating individuals (gametes) are differently constituted one from the other, whereas in the Infusoria they are almost always similar.

When the schizogony ceases, the merozoites, that had penetrated the epithelial cells and become trophozoites there, consist of two kinds of differently constituted individuals. One kind possesses a clear cytoplasm (fig. 67, XII), the other an opaque, richly granular cytoplasm (fig. 67, XI), while both possess a vesicular nucleus with a karyosome. In order to continue their development, the more granular individuals must be fertilized, and are therefore termed either female gametes or, on account of their size, macrogametes. The male individuals (microgametes) necessary to conjugation, are formed in greater numbers from the less dense microgametocytes or male mother-cells (fig. 67, XIId). They are slender bodies consisting chiefly of nuclear substance, and in most species bear two flagella of unequal length directed backwards, the place of insertion of which varies according to the species (fig. 67, XIIe).

While the development of the microgametes is rapidly advancing a change occurs in the nucleus of the female parent forms or macrogametocytes. Parts of the karyosome are extruded (fig. 67, XIc), and the nucleus loses at the same time its vesicular form. One macrogamete results, after nuclear maturation, from one macrogametocyte. By this time the macrogametes are capable of conjugation, and the process takes place within the host, generally, however, outside the affected and degenerated host cells. The microgametes that have now become free from the very large residual body, crowd around the mature macrogametes, which often send out a small prominence (“cone of reception” or fertilization protuberance) for their reception (fig. 67, XIII). As soon as a microgamete comes in contact with this and penetrates into the cytoplasm of the macrogamete, the latter surrounds itself with a membrane which prevents the intrusion of other microgametes. The nucleus of the microgamete that has gained entry unites with the nucleus of the macrogamete, which latter is afterwards capable of forming the well-known spores. The parasite is now called an encysted zygote or oöcyst. The oöcysts of some other members of the Coccidiidea, e.g., Eimeria avium, can form their walls prior to fertilization. In such cases, a weak spot is left at one place in the cyst wall, forming a micropyle, that permits of the entry of the male, immediately after which the micropyle is closed.

The reduced nucleus of the macrogamete elongates on the entry of the microgamete, and becomes a fertilization spindle to which the male pronucleus (from the microgamete) becomes attached (fig. 67, XIV and XV). Thereupon the spindle divides into two daughter nuclei (fig. 67, XVI) which assume a round shape. The protoplasm at this stage may at once divide, or another segmentation of the daughter nuclei may first occur. In the former case the two halves divide again, so that finally four nucleated segments, the sporoblasts, are formed, whereas in the latter case the four sporoblasts appear simultaneously (fig. 67, XVII). In both cases a residual body of varying size is separated from the protoplasm of the oöcyst. As a rule the oöcysts have already been discharged from the body of the host, and in the manner described above, form the sporoblasts after a longer or shorter period of incubation.

The sporoblasts are originally naked, but each soon secretes a homogeneous membrane, the sporocyst, in which it becomes enveloped (fig. 67, XVIII). After the segmentation of the nucleus the contents divide into two sickle-shaped sporozoites, in addition to which there is generally also a residual body (fig. 67, XIX).

This terminates the development. The spores are intended for the infection of other hosts. If they reach the intestine of suitable hosts, either free or enclosed in the oöcyst wall, the action of the intestinal juices causes them to open and permits the escape of the sporozoites (fig. 67, XX). The latter move exactly like the merozoites and soon make their way into epithelial cells (fig. 67, I), where they become schizonts, and thus repeat the life cycle.

Although our knowledge of the development of the coccidia is but of recent date, yet it already extends to a large number of species, which exhibit various deviations from the cycle of development described above. For instance, in addition to differences in the gametocytes, the schizonts of Adelea and Cyclospora also show differentiation and give rise to macromerozoites and micromerozoites, whilst in Adelea and Klossia a precocious association of the gametocytes precedes the true copulation of the ripe gametes.

The classification of the Coccidiidea is based chiefly on the number of sporozoites found in each spore, and the number of sporocysts (spores) found in one oöcyst. Léger[173] recognises two great legions, the Eimeridea and the Adeleidea, the former comprising the greater number of genera, including the genus of most economic importance, Eimeria. It must be noted that, though a member of this genus may be frequently referred to as Coccidium, strictly it should be termed Eimeria, that name having priority. The name of the disease resulting from the action of such parasites is, however, established and remains as coccidiosis.

[173] Arch. f. Protistenkunde (1911), xxii, p. 71.

Certain of the more important of the Coccidiidea may now be considered.

Genus. *Eimeria*, Aimé Schneider, 1875.

Syn.: Psorospermium, Rivolta, 1878; Cytospermium, Rivolta, 1878; Coccidium, R. Leuckart, 1879; Pfeifferia, Labbé, 1894; Pfeifferella, Labbé, 1899.

The Eimeria belong to Léger’s old family, the Tetrasporocystidæ, which comprises forms producing oöcysts with four sporocysts, each containing two sporozoites. The cysts are spherical or oval, as are also usually the schizonts. The members of the genus are confined chiefly to vertebrate hosts, the more important economically occurring in mammals and birds. From the mammalian hosts very rarely the parasites may reach man. Eimeria (Coccidium) avium of wild birds and poultry, and Eimeria stiedæ parasitic in rabbits, may be considered. There is a general similarity in their life-cycles and each is of great practical importance.

*Eimeria avium*, Silvestrini and Rivolta.

Eimeria avium is responsible for fatal epizoötics among game birds such as grouse, pheasants and partridges, and domestic poultry such as fowls, ducks, pigeons and turkeys, and can pass from any one of these hosts to any of the others with the same effect. The organism is parasitic in the alimentary tract of the host, affecting more especially the small intestine (duodenum) and the cæca, but in some cases penetrating to the liver and multiplying there (as in turkeys), producing necrotic cheesy patches, that ultimately become full of oöcysts. The gut is rendered very frail by the action of the parasites, its mucous membrane is greatly injured, and is often reduced to an almost structureless pulp, riddled with parasites (fig. 68). Infection is conveyed from host to host by the ingestion of food or drink contaminated with the oöcysts voided in the fæces of infected birds. Oval oöcysts from 24 µ to 35 µ long and from 14 µ to 20 µ broad are the means of infection. The oöcysts develop internally four sporocysts or spores, from each of which two sporozoites are produced. The life-history[174] presents two phases: (1) The asexual multiplicative phase, schizogony, for the increase in numbers of the parasites within the same host; (2) the reproductive phase, following the formation of gametes (gametogony), leading to the production of resistant oöcysts, destined for the transference of the parasite to new hosts (sporogony).

[174] Fantham, H. B. (1910), “The Morphology and Life History of Eimeria (Coccidium) avium, a Sporozoön causing a fatal disease among young Grouse,” Proc. Zool. Soc. Lond., 1910, pp. 672–691, 4 plates. Also Fantham, H. B. (1911), “Coccidiosis in British Game Birds and Poultry,” Journ. Econ. Biol., vi, pp. 75–96.

The oöcysts usually reach the duodenum unharmed, with food or drink. Under the influence of the powerful digestive juices (especially the pancreatic) now encountered, the oöcysts soften, as do the sporocysts, and ultimately two sporozoites emerge from each sporocyst. The sporozoites are from 7 µ to 10 µ long, and each is vermicular with a uniform nucleus (fig. 69, A). After a short period of active movement in the gut, each sporozoite penetrates an epithelial cell (figs. 68 spz, 69, B), and once within, gradually becomes rounded (fig. 69, B, C). It grows rapidly, feeding on the contents of the host cell and living as a trophozoite (fig. 69, D). When the parasite is from 10 µ to 12 µ in diameter, usually multiplication by schizogony (fig. 69, E-H) begins. The nucleus of the parent cell, now called a schizont, divides into a number of portions that become arranged at the periphery (fig. 69, E). Cytoplasm collects around each nucleus (fig. 69, E, F) and gradually a group of daughter individuals (merozoites) is produced (fig. 69, G), the nucleus of each merozoite showing a karyosome.

The merozoites of Eimeria avium are arranged “en barillet,” like the segments of an orange (figs. 68 mz, 69, G), therein differing from those of E. schubergi, which are arranged “en rosace.” They separate from one another (fig. 69, H), penetrate other epithelial cells, where they may, in turn, become schizonts. Eight to fourteen merozoites are usually formed by each schizont, twenty have been found, while in cases of intense infection when space has become limited, the number may be only four.

After a number of generations of merozoites have been formed, a limit is reached both to the multiplicative capacity of the parasite and to the power of the bird to provide the invader with food. Consequently, resistant forms of the parasite are necessary, and the trophozoites begin to show sexual differentiation instead of forming schizonts, that is, gametogony commences.

Certain trophozoites store food and become large and granular. These are macrogametocytes (fig. 69, I, ♀). The microgametocytes (fig. 69, I, ♂) are smaller and far less granular. The macrogametocyte continues to grow, and becomes loaded with chromatoid and plastinoid granules (fig. 69, J, ♀), while the microgametocyte has its nucleus divide to form a number of bent, rod-like portions (fig. 69, J, ♂). The macrogametocyte gives rise to a single macrogamete, which forms a cyst wall for itself, leaving a thin spot (micropyle) for the entry of the male (fig 69, K, ♀). The microgametocyte gives rise to numerous small, biflagellate microgametes (fig. 69, K, ♂) around a large, central residual mass, from which they ultimately break free, and swim away. When a macrogamete is reached, the microgamete enters through the micropyle (fig. 69, L)--which then closes, thus excluding the other males--and applies itself to the female nucleus (fig. 69, M). Nuclear fusion occurs, the oöcyst (encysted zygote) being thus produced. Sporogony then ensues. The oöcyst (fig. 69, N) at first has its contents completely filling it. They then concentrate into a central spherical mass (fig. 69, O) which gradually becomes tetranucleate (fig. 69, P). Cytoplasm collects around each nucleus, and four sporoblasts are thus formed (fig. 69, Q). Each sporoblast becomes oval (fig. 69, R) and produces a sporocyst. Ultimately two sporozoites are formed in each sporocyst or spore, at first lying tête-bêche (fig. 69, S), but finally twisting to assume the position most convenient for emergence (fig. 69, T) when they reach a new host. The period of the life-cycle of Eimeria avium (as well as the details of the life-cycle) was determined by Fantham to be from eight to ten days, of which period schizogony occupies four to five days.

The method of infection[175] is contaminative, by way of food or drink. Young birds are especially susceptible to infection. Certain birds, particularly older ones, may act as reservoirs of oöcysts, being continuously infected themselves, without showing any marked ill effects from the parasite, but being highly infectious to other birds. Much moisture retards the development of sporocysts considerably. The duration of vitality of the infective oöcysts has been determined experimentally to extend well over two years, and in certain cases longer. Eimeria avium is the causal agent of “white diarrhœa” or “white scour” in fowls, and of “blackhead” in turkeys.

[175] Fantham, H. B. (1910), “Experimental Studies on Avian Coccidiosis, especially in relation to young Grouse, Fowls and Pigeons,” Proc. Zool. Soc. Lond., 1910, pp. 722–731, 1 plate.

Eimeria avium of birds and E. stiedæ of rabbits closely resemble one another, but are not the same parasite, for E. avium is not infective to rabbits, nor E. stiedæ to poultry.

*Eimeria stiedæ*, Lindemann, 1865.

Syn.: Monocystis stiedæ, Lindemann, 1865; Psorospermium cuniculi, Rivolta, 1878; Cytospermium hominis, Rivolta, 1878; Coccidium oviforme, Leuckart, 1879; Coccidium perforans, Leuckart, 1879; Coccidium cuniculi.

Eimeria stiedæ is parasitic in the gut epithelium (fig. 70), liver, and epithelium of the bile ducts of rabbits, and is usually considered to be the parasite very occasionally found in man. The life-cycle resembles that of Eimeria avium in its general outlines (see fig. 69) and therefore will not be detailed in full here. The oöcysts (fig. 71) are large, elongate-oval, greenish in fresh preparations and vary in size from 24 µ to 49 µ long and 12·8 µ to 28 µ broad, the gut forms being usually smaller than those occurring in the liver, owing to the more confined space in which they are formed. Formerly, the parasites in the liver were described under the name of Coccidium oviforme, while those from the intestine were termed Coccidium perforans. This distinction has now broken down.

The oöcysts[176] are thick-walled, somewhat flattened at one pole, where a large micropyle is present. Four egg-shaped spores (sporocysts) are formed within, each about 12 µ to 15 µ long and 7 µ broad (fig. 72). The oöcysts are voided with the fæces. Sporogony takes, in nature, about three days in the excrement. Fæcal contamination of the food of rabbits results, and coccidian oöcysts are swallowed. Under the influence of the pancreatic juice of a new host, the sporozoites (fig. 72, a--c) are liberated from the spores and proceed to attack the epithelium and multiply within it, as in the case of Eimeria avium. From the gut, infection spreads to the liver, where multiplication of the parasite goes on actively, resulting in the formation of the whitish coccidial nodules, which may be very conspicuous (fig. 74). Proliferation of the connective tissue may occur around the coccidial nodules, which then contain large numbers of oöcysts in various stages of development. It is said that the oöcysts in the older nodules do not seem to be capable of further development. Schizogony (fig. 73) and gametogony in all stages can be found in both liver and gut.

[176] For an account of the life-cycle of Eimeria stiedæ consult Wasielewski, Th. von (1904), “Studien und Photogramme zur Kenntnis der pathogenen Protozoen,” Heft. 1 (Coccidia), 118 pp., 7 plates, Leipzig: J. A. Barth. Also, Metzner, R. (1903), Arch. f. Protistenk., ii, p. 13.

Young rabbits often die of intestinal coccidiosis before infection of the liver occurs. The repeated schizogony of Eimeria stiedæ in the gut is sufficient to cause death.

The disease of cattle popularly known as “red dysentery” is also ascribed to the action of Eimeria stiedæ. The fæces of infected cattle show blood clots of various sizes and in severe cases watery diarrhœa is present. Acute cases end fatally in about two days. Numerous oöcysts, considered to be those of Eimeria stiedæ, occur in the fæces, and there is a heavy infection of the gut, especially the large intestine and rectum, all stages of the parasite being found in the epithelium. It is suspected that cattle contract the disease by feeding on fresh grass contaminated with oöcysts. The disease is recorded from Switzerland and from East Africa.

As before mentioned, Eimeria stiedæ is considered to be the organism found in a few cases in man, possibly acquired by eating the insufficiently cooked livers of diseased rabbits. These cases may now be described.

(a) *Human Hepatic Coccidiosis.*

(1) Gubler’s Case. A stone-breaker, aged 45, was admitted to a Paris hospital suffering from digestive disturbances and severe anæmia. On examination the liver was found to be enlarged and presented a prominent swelling, which was regarded as being due to Echinococcus. At the autopsy of the man, who succumbed to intercurrent peritonitis, twenty cysts were found averaging 2 to 3 cm. in diameter, and one measuring 12 to 15 cm. The caseous contents consisted of detritus, pus corpuscles, and oval-shelled formations, which were considered to be Distoma eggs, but which, in accordance with Leuckart’s conjecture, proved to be Coccidia.[177]

[177] Gubler, A., “Tumeurs du foie déterm. par des œufs d’helm....” Mem. Soc. Biol., Paris, 1858, v, 2; and Gaz. med. de Paris, 1858, p. 657; Leuckart, R., Die menschl. Paras., 1863, 1ST edition, i, pp. 49, 740.

(2) Dressler’s Case (Prague). Relates to three cysts, varying from the size of a hemp-seed to that of a pea, and containing Coccidia, found in a man’s liver.[178]

[178] Leuckart, R., Die menschl. Paras., 1863, 1st edition, i, p. 740.

(3) Sattler’s Case (Vienna). Coccidia were in this case observed in the dilated biliary duct of a human liver.[179]

[179] Leuckart, R., Die Paras. d. mensch., 1879, 2nd edition, p. 281.

(4) Perls’ Case (Giessen). Perls discovered Coccidia in an old preparation of Sömmering’s agglomerations.[180]

[180] Leuckart, R., ibid., p. 282.

(5) Silcock’s Case (London).[181] The patient, aged 50, who had fallen ill with serious symptoms, exhibited fever, enlarged liver and spleen, and had a dry, coated tongue. At the autopsy numerous caseous centres, mostly immediately beneath the surface, were found, while the contiguous parts of the liver were inflamed. Microscopical examination demonstrated numerous Coccidia in the hepatic cells as well as in the epithelium of the biliary ducts. A deposit of Coccidia was likewise found in the spleen, which the parasites had probably reached by means of the blood-stream.[182]

[181] Silcock, “A Case of Parasit. by Psorospermia,” _Trans. Path. Soc._, London, 1890, xli, p. 320.

[182] Pianese has confirmed the fact that Coccidia actually occur in the blood of the hepatic veins of infected rabbits.

(b) *Human Intestinal Coccidiosis.*

In two cadavers at the Pathological Institute in Berlin, Eimer[183] found the epithelium of the intestine permeated by Coccidia. Railliet and Lucet’s case may be traced back to intestinal Coccidia, which were found in the fæces of a woman and her child, who had both suffered for some time from chronic diarrhœa.[184] In other cases (Grassi, Rivolta), where only the existence of Coccidia in the fæces was known, it is doubtful whether the parasites originated in the intestine or in the liver.

[183] Die ei- u. kugelf. Psorosp. d. Wirbelt., 1870, p. 16.

[184] Railliet and Lucet, “Obs. s. quelq. Cocc. intest.,” _C. R. Soc. Biol._, Paris, 1890, p. 660; Railliet, Trait. Zool. med. et agric., 2e éd., 1895, p. 140.

(c) *Doubtful Cases.*

To these belong Virchow’s case[185] where, in the liver of an elderly woman, a thick walled tumour measuring 9 to 11 mm. was found. Among the contents of this tumour there were oval formations 56 µ long, surrounded by two membranes and enclosing a number of round substances. Virchow considered these foreign bodies to be eggs of pentastomes in various stages of development, others consider them to be Coccidia.

[185] Arch. f. path. An., xviii, 1860, p. 523.

The Coccidia which Podwyssotzki claims to have seen in the liver of a man, not only in the liver cells, but also in the nuclei, are also problematic.[186] The parasite was called Caryophagus hominis.

[186] Podwyssotzki, “Ueb. d. Bedeut. d. Coccid. in d. Path. Leber des Menschen,” Centralbl. f. Bakt., vi, 1889, p. 41.

Again, other explanations can be given to an observation by Thomas, on the occurrence of Coccidium oviforme in a cerebral tumour of a woman aged 40. The growth was as large as a pea and surrounded by a bony substance.[187]

[187] Thomas, J., “Case of Bone Formation in the Human Brain, due to the Presence of Coccidium oviforme,” Journal Boston Soc. Med. Sc., iii, 1899, p. 167; Centralbl. f. Bakt. [I] xxviii, 1900, p. 882.

Genus. *Isospora*, Aimé Schneider, 1881.

Syn.: Diplospora, Labbé, 1893.

Belonging to the section Disporea, that is, forming only two spores, each with four sporozoites.

*Isospora bigemina*, Stiles, 1891.

Syn.: “Cytospermium villorum intestinalium canis et felis,” Rivolta, 1874; “Coccidium Rivolta,” Grassi, 1882; Coccidium bigeminum, Stiles, 1891.

This parasite lives in the intestinal villi of dogs, cats, and the polecat (Mustela putorius, L.). According to Stiles,[188] the oöcyst divides into two equal ellipsoidal portions or sporoblasts which become spores and then each forms four sporozoites. The oöcysts of this species vary from 22 µ to 40 µ in length and from 19 µ to 28 µ in breadth. Each spore is 10 µ to 18 µ long and contains four sporozoites. The parasites live and multiply, not only in the gut epithelium, but also in the connective tissue of the intestinal submucosa. Wasielewski has seen merozoites in the gut of the cat.

[188] “Notes on Paras.,” No. II, Journ. of Comp. Med. and Vet. Sci., 1892, xiii, p. 517.

Isospora bigemina (fig. 75) appears to occur also in man, for Virchow published a case which was communicated to him by Kjellberg, and attributed the illness to this parasite.[189] Possibly also it would be more correct to ascribe the observation of Railliet and Lucet, which is mentioned under “Human Intestinal Coccidiosis,” p. 148, to this species, as the Coccidia in that case were distinguished by their diminutive size (length 15 µ, breadth 10 µ). The case communicated by Grunow may also possibly refer to Isospora bigemina.[190] Roundish or oval structures of 6 µ to 13 µ in diameter occurred in the mucous membrane of the gut and in the fæces of a case of enteritis.

[189] Arch. f. path. An., 1860, xviii, p. 527.

[190] Grunow, “Ein Fall von Protozoën (Coccidien?) Erkrankung des Darmes,” Arch. f. exper. Path. und Pharm., 1901, xlv, p. 262.

DOUBTFUL SPECIES.

In literature many other statements are found as to the occurrence of Coccidia-like organisms in different diseases of man. In some of the cases the parasites proved to be fungi. This was the case with the parasites of a severe skin disease of man, formerly called Coccidioides immitis and Coccidioides pyogenes. Other statements are founded on misapprehensions, or are still much disputed. If reference is here made to “Eimeria hominis,” R. Blanchard, 1895, this is done on the authority of the investigator mentioned. The structures in question are nucleated spindle-shaped bodies of very different lengths (18 µ to 100 µ), which either occurred isolated or were enclosed in large globular or oval cysts, alone or with a larger tuberculated body (“residual body”). These formations were found by J. Künstler and A. Pitres in the pleural exudation removed from a man by tapping. The man was employed on the ships plying between Bordeaux and the Senegal River.

Blanchard looks upon the fusiform bodies as merozoites and the cysts as schizonts of a Coccidium. On the other hand, Moniez declares the spindle bodies to be the ova and the supposed residual bodies to be “floating ovaries” of an Echinorhynchus.

Severi’s “monocystid Gregarines,” which were taken from the lung tissue of a still-born child, are also quite problematical.

No less doubtful are the bodies which Perroncito calls Coccidium jalinum, and which he found in severe diseases of the intestine in human beings, pigs, and guinea-pigs; Borini also reported another case.

Order. *Hæmosporidia*, Danilewsky emend. Schaudinn.

The Hæmosporidia are a group of blood parasites, comprising forms differing greatly among themselves. Some of the forms need much further investigation. However, there are certain true Hæmosporidia which present close affinities with the Coccidia, leading Doflein to use the term *Coccidiomorpha* for the two orders conjoined.

The Hæmosporidia present the following general characteristics:--

(1) They are parasites of either red or white blood corpuscles of vertebrates during one period of their life-history.

(2) They exhibit alternation of generations--asexual phases or schizogony alternating with sexual phases or sporogony--as do the Coccidia.

(3) There is also an alternation of hosts in those cases which have so far been completely investigated. The schizogony occurs in the blood or internal organs of some vertebrates while the sporogony occurs in an invertebrate, such as a blood-sucking arthropod or leech.

(4) Unlike the Coccidia, resistant spores in sporocysts are not generally produced, such protective phases in the life-cycle being unnecessary, as the Hæmosporidia are contained within either the vertebrate or invertebrate host during the whole of their life.

The Hæmosporidia may be considered for convenience under five main types:--

(1) The Plasmodium or Hæmamœba type. This includes the malarial parasites of man and of birds. The asexual multiplicative or schizogonic phases occur inside red blood corpuscles and are amœboid. They produce distinctive, darkish pigment termed melanin or hæmozoin. Infected blood drawn and cooled on a slide may exhibit “exflagellation” of the male gametocytes, i.e., the formation of filamentous male gametes. The invertebrate host is a mosquito. The malarial parasites of man are discussed at length on p. 155. Similar pigmented hæmamœboid parasites have been described in antelopes, dogs, and other mammals, and even reptiles.

(2) The Halteridium type. The trophozoite stage inside the red blood corpuscle is halter-shaped. Pigment is produced, especially near the ends of the organism. The parasites occur in the blood of birds. The invertebrate host of H. columbæ of pigeons in Europe, Africa, Brazil and India, is a hippoboscid fly, belonging to the genus Lynchia.

Halteridium parasites are common in the blood of passerine birds, such as pigeons, finches, stone owls, Java sparrows, parrots, etc. The Halteridium embraces or grows around the nucleus of the host red cell without displacing the nucleus. Young forms and multiplicative stages of H. columbæ have been found in leucocytes in the lungs of the pigeon (fig. 76, 8-12). Male and female forms (gametocytes) are seen in the blood (fig. 76, 3a, 3b). The cytoplasm of the male gametocytes is pale-staining and the nucleus is elongate, while the cytoplasm of the females is darker and the nucleus is smaller and round. Formation of male gametes from male gametocytes (the so-called process of “exflagellation”) may occur on a slide of drawn infected blood, also fertilization, and formation of the oökinete, as first seen by MacCallum. The correct generic name for Halteridia is, apparently, Hæmoproteus. Wasielewski (1913), working on H. danilewskyi (var. falconis), in kestrels, finds that the halteridium may be pathogenic to nestlings. The cycle of H. noctuæ described by Schaudinn (1904) lacks confirmation. The account of the life-cycle of H. columbæ given by Aragão (1908) is illustrated in fig. 76. It agrees with the work of Sergent (1906–7) and Gonder (1915). Mrs. Adie (1915) states that the cycle in Lynchia is like that of a Plasmodium.

(3) The Leucocytozoön type. The trophozoites and gametocytes occur within mononuclear leucocytes and young red cells (erythroblasts) in the blood of birds. Laveran and França consider that the Leucocytozoa occur in erythrocytes. The host cells are often greatly altered by the parasites, becoming hypertrophied and the ends usually drawn into horn-like processes (fig. 77), though some remain rounded. Leucocytozoa are limited to birds, and very rarely produce pigment. Male and female forms (gametocytes) are distinguishable in the blood (fig. 77), and the formation of male gametes (“exflagellation”) may occur in drawn blood.

The Leucocytozoa were first seen by Danilewsky in 1884. They are usually oval or spherical. It is not easy sometimes to distinguish the altered host cell from the parasite, as the nucleus of the former is pushed to one side by the leucocytozoön. The cytoplasm of the female parasite stains deeply, and the nucleus is rather small, containing a karyosome. In the male the cytoplasm stains lightly and the nucleus is larger, with a loose, granular structure.

Many species of Leucocytozoa are recorded, but schizogony has only been described by Fantham (1910)[191] in L. lovati in the spleen of the grouse (Lagopus scoticus), and by Moldovan[192] (1913) in L. ziemanni in the internal organs of screech-owls.

[191] Annals Trop. Med. and Parasitol., iv, p. 255.

[192] Centralbl. f. Bakt., Orig., lxxi, p. 66.

M. and A. Leger[193] (1914) propose to classify Leucocytozoa, provisionally, according as the host cells are fusiform or rounded.

[193] Bull. Soc. Path. Exot., vii, p. 437.

(4) The Hæmogregarina type. Included herein are many parasites of red blood corpuscles, with a few (the leucocytogregarines) parasitic in the white cells of certain mammals and a few birds. They are not amœboid but gregarine-like, vermicular or sausage-shaped (fig. 78). They do not produce pigment. They are widely distributed among the vertebrata, but are most numerous in cold-blooded vertebrates (fishes, amphibia and reptiles). The hæmogregarines of aquatic hosts are transmitted by leeches, those of terrestrial hosts by arthropods.

The nucleus of hæmogregarines is usually near the middle of the parasite, but may be situated nearer one end. The body of the parasite may be lodged in a capsule (“cytocyst”). There is much variation in size and appearance among hæmogregarines. Some are small (Lankesterella); some attack the nucleus of the host cell (Karyolysus); others have full grown vermicules larger than the containing host corpuscle, and so the hæmogregarines bend on themselves in the form of *U* (fig. 78, b). Schizogony often occurs in the internal organs of the host, sometimes in the circulating blood.

The hæmogregarines occurring in the white cells (mononuclears or polymorphonuclears) of mammals have been referred to a separate genus, Leucocytogregarina (Porter) or Hepatozoön (Miller). Such leucocytogregarines are known in the dog (fig. 79), rat, mouse, palm-squirrel, rabbit, cat, etc. Schizogony of these forms occurs in the internal organs, such as the liver, lung and bone-marrow of the hosts. They are apparently transmitted by ectoparasitic arthropods, such as ticks, mites, and lice.

A few hæmogregarines are known to be parasitic in the red blood corpuscles of mammals. Such are H. gerbilli in the Indian field rat, Gerbillus indicus; H. balfouri (jaculi) in the jerboa, Jaculus jaculus, and a few species briefly described from marsupials. These parasites do not form pigment.

Strict leucocytic gregarines have been described from a few birds by Aragão and by Todd.

The sporogony of hæmogregarines is only known in a few cases, and in those affinity with the Coccidia is exhibited. In fact, the Hæmogregarines are now classified by some authors with the Coccidia.

(5) The Babesia or Piroplasma type. These are small parasites of red blood corpuscles of mammals. They do not produce pigment. They are pear-shaped, round or amœboid in Babesia, bacilliform and oval in other forms referred to this group. Piroplasms are transmitted by ticks. These parasites are described at length on p. 172.

THE MALARIAL PARASITES OF MAN.

Malaria, otherwise known as febris intermittens, chill-fever, ague, marsh fever, paludism, etc., is the name given to a disease of man, which begins with fever. It has been known since ancient times and is distributed over almost all the world, although very unevenly, but does not occur in waterless deserts and the Polar regions. In many places, especially in the civilized countries of Central Europe, the disease is extinct or occurs only sporadically, and large tracts of land have become free from malaria.

The rhythmical course of the fever is characteristic. It begins apparently suddenly with chilliness or typical shivering, whilst the temperature of the body rises, the pulse becomes low and tense and the number of beats of the pulse increases considerably. After half to two hours the heat stage begins. The patient himself feels the rise of his temperature (shown by feeling of heat, dry tongue, headache, thirst). The temperature may reach 41°C or more. At the same time there is sensitiveness in the region of the spleen and enlargement of that organ. After four to six hours an improvement takes place, and with profuse perspiration the body temperature falls rapidly, not often below normal. After the attack the patient feels languid, but otherwise well until certain prodromal symptoms (heaviness in the body, headache) which were not noticed at first, denote the approach of another attack of fever, which proceeds in the same way.

The intervals between the attacks are of varying length which permit of a distinction in the kinds of fever. If the attacks intermit one day, occurring on the first, third and fifth days of the illness and always at the same time of day, it is termed febris tertiana; if two days occur between fever days, it is called febris quartana. In the case of the fever recurring daily, later writers speak of typical febris quotidiana. But a quotidian fever may arise when two tertian fevers differing by about twenty-four hours exist at the same time (febris tertiana duplex). The patient has a daily attack, but the fever of the first, third and fifth days differs in some point (hour of occurrence, height of temperature, duration of cold or hot stage) from the fever of the second, fourth and sixth days. Similarly, two or three quartan fevers which differ by about twenty-four hours each may be observed together (febris quartana duplex or triplex); in the latter case the result is also a quotidian fever.

Two kinds of tertian fever are differentiated--a milder form occurring especially in the spring (spring tertian fever), and a more severe form appearing in the summer and autumn in warmer districts, especially in the tropics (summer or autumn fever, febris æstivo-autumnalis, febris tropica, febris perniciosa). The latter often becomes a quotidian fever.

All the afore-mentioned infections are termed acute. They are distinguished from the very different chronic malarial infection by the frequent occurrence of relapses, which finally lead to changes of some organs and particularly of the blood. The relapses are then generally marked by an irregular course of fever.

The term masked malaria is used when any disturbance of the state of health of a periodic character shows itself and disappears after treatment with quinine.[194] Generally it is a question of neuralgia.

[194] Quinine is still almost exclusively the remedy used in the treatment of malaria. It is prepared from the bark of the cinchona tree. This important remedy was introduced into Europe in 1640 from Ecuador by Juan del Vego, physician of the Countess del Cinchon.

That intermittent fever was an infectious disease, although not one which was transmitted direct from man to man, had been assumed for a long time. Therefore it was natural, at a time when bacteriology was triumphing, to look for a living agent causing infection in malaria, which search was, seemingly, successful (Klebs, Tomasi-Crudeli, 1879). Hence it was not surprising that the discovery of the real malarial parasites in November, 1880, by the military doctor A. Laveran[195] in Constantine (Algeria), at first met with violent opposition, even after Richard (1882) had confirmed it and Marchiafava, Celli, Grassi and others, had further extended it. Not that the existence of structures found in the blood of malaria patients by Laveran and Richard was denied; on the contrary, the investigations of the opponents furnished many valuable discoveries, but the organisms were differently interpreted and considered to be degeneration products of red blood corpuscles. Only when Marchiafava and Celli (1885) saw movements in the parasites, which Laveran called Oscillaria malariæ and later Hæmatozoön malariæ, was their animal nature admitted and the parasites were named Plasmodium malariæ. Shortly before this, Gerhardt (1884) had stated that the disease could be transmitted by the injection of the blood of a malarial patient to a healthy person.

[195] The discovery of Laveran is in no way lessened by the fact that one investigator or another (according to Blanchard [Arch. de Paras., vii, 1903, p. 152], P. F. H. Klencke in 1843) had seen, mentioned and depicted malarial parasites. (Neue phys. Abhandl. auf. selbständ. Beob. gegr., Leipzig, 1843, p. 163, fig. 25). In 1847 Meckel had recognized that the dark colour of the organs in persons dead of malaria was due to pigment. Virchow in 1848 stated that this pigment occurred in blood cells. Kelsch in 1875 recognized the frequency of melaniferous leucocytes in the blood of malarial patients. Beauperthuy (1853) noticed that in Guadeloupe there was no malaria at altitudes where there were no “insectes tipulaires,” and suggested that the disease was inoculated by insects.

This supplied the starting point for further investigations, which were made not exclusively, but principally, by Italian investigators (Golgi, Marchiafava and Celli, Bignami and Bastianelli, Grassi and Feletti, Mannaberg, Romanowsky, Osier, Thayer and others). In 1885 Golgi described the asexual cycle in the blood, in the case of the quartan parasite. These investigations, after attention had been drawn by Danilewsky (1890) to the occurrence of similar endoglobular parasites in birds, were extended to the latter (Grassi and Feletti, Celli and Sanfelice, Kruse, Labbé and others).

The result was as follows: Malaria in man (and birds) is the result of peculiar parasites included in the Sporozoa by Metchnikoff, which parasites live in the erythrocytes, grow in size and finally “sporulate,” that is, separate into a number of “spores” which leave the erythrocytes and infect other blood corpuscles. Morphologically and biologically several species (and respectively several varieties) of malarial parasites may be distinguished, on which the different intermittent forms depend. Transmission of the blood of patients to healthy people produces a malarial affection which corresponds in character to the fever of the patient from whom the inoculation was made. The combined types of fever (tertiana duplex, quartana duplex or triplex) are explained by the fact that the patient harbours two or three groups of parasites which differ in their development by about twenty-four hours, whilst the irregular fevers depend on deviation from the typical course of development of the parasites. In addition to stages of the parasites which could easily be arranged in a developmental series concurrent with the course of the disease, other phases of the parasites also became known, such as spheres, crescents, polymitus forms, which seemed not to be included in the series and, therefore, were very differently interpreted.

The decision reached at the beginning of the last decade of the last century, which found expression in comprehensive statements (Mannaberg, Ziemann and others), only concerned a part of the complete development of the malarial parasites. No one could with any degree of certainty demonstrate how man became infected, nor were there reliable hypotheses based on analogy with other parasites concerning the exit of the excitants of malaria from the infected person and their further behaviour. Numerous hypotheses had been advanced, but none was able to elucidate the various observations made from time to time in dealing with malaria. One hypothesis only seemed to have a better foundation. Manson (1894), who knew from his own experience the part played by mosquitoes in the development of Filaria from the blood of man, applied this also to the malarial parasites living in the blood, whereby at least the way was indicated by which the Hæmosporidia could leave man. The parasites were said finally to get into water through mosquitoes which had sucked the blood of malarial patients, and the germ spread thence to men who drank the water. In some cases the parasites were supposed to reach man by the inhaling of the dust of dried marshes. On the other hand, Bignami believed that the mosquitoes were infected in the open air by malarial parasites which occurred there in an unknown stage and the insects transmitted the germs to man when biting. R. Koch combined both hypotheses, without, however, producing positive proof. R. Ross, then (1897–8) an English military doctor in India, was the first to succeed in this. He had been encouraged by Manson to study the fate of malarial Plasmodia which had entered the intestine of mosquitoes with malaria-infected blood, especially in the case of the Plasmodium (Proteosoma) living in the blood of birds. He showed that the Proteosoma penetrate the intestinal wall of the mosquitoes, grow and develop into large cysts which produce innumerable rod-like germs, which burst into the body cavity and penetrate the salivary glands. Ross allowed mosquitoes to suck the blood of birds affected by malaria, and some nine days later, let the infected mosquitoes which had been isolated suck healthy birds. After five to nine days Proteosoma were found to occur in the blood of the birds used. The Proteosoma and Halteridium of birds were also further investigated by MacCallum (1897–8), Koch and others, and important results followed.

In any case Ross (1898) had clearly established the importance of mosquitoes in the spread of malaria among birds. It was now only a question of proving whether, and how far, mosquitoes were concerned with human malaria. Ross himself worked to this end. Here the experiments of Italian investigators (Bignami, Bastianelli, Grassi)[196] were of importance. These investigators studied the fate of malarial parasites in man, produced malaria in men experimentally by the bites of infected mosquitoes, and established that only mosquitoes belonging to the genus Anopheles were concerned, and not species of Culex. These latter are only able to transmit Proteosoma to birds. It is true that Culex can ingest the human malarial parasites, but the latter do not develop in them. Development only occurs in species of Anopheles. In Anopheles (and similarly for Proteosoma in Culex) sexual reproduction takes place; crescents, spheres and polymitus forms are necessary stages of development in the mosquito.

[196] Grassi, B. (1901), “Die Malaria,” 250 pp., 8 plates. G. Fischer, Jena.

With these discoveries the campaign against malaria became more definite. It was directed partly against the transmitters, whose biology and life-cycle were more thoroughly investigated, instead of merely against the infection of the adult Anopheles. The latter do not, as was believed for some time, transmit the malarial germs to their offspring. They always infect themselves from human beings, whereby the relapses appearing in early summer, and the latent infection, especially of children of natives, play a principal part (Stephens and Christophers, Koch). Further, the crusade was directed against the infection of man by the bites of Anopheles. Important results have been obtained in these directions. Low and Sambon in 1900 lived in a mosquito-screened hut in a malarial part of the Roman Campagna for three of the most malarious months and did not contract the disease. In the same year Dr. P. T. Manson was infected with malaria by infected mosquitoes sent from Italy. The rôle of mosquitoes having been proved, it may be hoped that ultimately the eradication of malaria, or at least a considerable restriction of it, will be achieved.

It is of importance to record that, although malarial parasites occur in mammals (monkeys, bats, etc.) the human ones are not transmissible to mammals, not even to monkeys. The species, therefore, are specific to the different hosts (Dionisi, Kossel, Ziemann, Vassall).

An important work dealing with the modern applications of the mosquito-malaria theory in all parts of the Tropics was published by Sir Ronald Ross in 1911. It is entitled “The Prevention of Malaria” (John Murray, London, 21s.).

DEVELOPMENT OF THE MALARIAL PARASITES OF MAN.

The commencement of the developmental cycle and of the infection of man, is the sporozoites (fig. 80, 1) which are passed into the blood of a person by the bite of an infected mosquito. Prior to this the parasites collect in the excretory ducts of the salivary glands (fig. 80, 27) of the Anopheles. The sporozoites are elongate and spindle-shaped, 10 µ to 20 µ long and 1 µ to 2 µ broad, with an oval nucleus situated in the middle. They are able to glide, perform peristaltic contractions, or curve laterally. Schaudinn has studied the penetration of the red blood corpuscles (fig. 80, 2) by the sporozoites in the case of the living tertian parasite. The process takes forty to sixty minutes in drawn blood. After its entrance the parasite, which is now called a trophozoite, contracts, and becomes an active amœbula (fig. 80, 3). It develops a food vacuole and grows at the expense of the invaded blood corpuscle (fig. 80, 4), which is shown by the appearance of pigment granules (transformed hæmoglobin) in it. When the maximum size is attained, multiplication by schizogony (fig. 80, 5-7) begins with a division of the nucleus, which is followed by further divisions of the daughter nuclei, the number of which varies up to 16 or even 32, depending on the species of the parasite. Then the cytoplasm divides into as many portions as there are nuclei, the result being a structure suggestive of the spokes of a wheel or of a daisy, the centre of the resulting rosette being occupied by dark pigment. Finally, the parts separate from one another, leaving behind a residual body containing the pigment, and the daughter forms issue into the blood plasma as merozoites (fig. 80, 7). They are actively amœboid (fig. 80, 8) and soon begin to enter other blood corpuscles of their host, for the entry into which thirty to sixty minutes are necessary, according to Schaudinn’s observations.[197]

[197] It should be remembered that some authors (Laveran, Argutinsky, Panichi, Serra) argue against the intra-globular position of malarial parasites and state that they only adhere outwardly to the red blood corpuscles. These views have recently been revived by Mary Rowley-Lawson, and she states that the malarial parasite is “extracellular throughout its life-cycle and migrates from red corpuscle to red corpuscle destroying each before it abandons it.” (Journ. Exper. Med., 1914, xix, p. 531.)

Here they behave like sporozoites which previously entered and again produce merozoites. This process is repeated until the number of parasites is so large that, at the next migration of the merozoites, the body of the person infected reacts with an attack of fever,[198] which is repeated with the occurrence of the next or following generations.

[198] The incubation period, that is, the time between infection and the first attack of fever, is ten to fourteen days; with severe infection fewer days (minimum 5 to 6) are needed.

The growth and schizogony last different times, according to the species of the parasite, about forty-eight hours in the case of the parasite of febris tertiana or tropica, and seventy-two hours for the quartan parasite. The various intermittent forms produced by them depend on this specific difference in the malarial parasites.

The schizogony can, however, only be repeated a certain number of times, supposing that the disease has not been checked prematurely by the administration of quinine, which is able to kill the parasites. It appears that after a number of attacks of fever the conditions of existence in man are unfavourable for the malarial parasites, and this brings about the production of other forms which have long been known, but also long misunderstood (spheres, crescents, polymitus). The merozoites in this case no longer grow into schizonts, or at least not all of them, but become sexual individuals called gametocytes (fig. 80, 9-12), which only start their further development when they have reached the intestine of Anopheles. This does not take place in every case, nor with all the gametocytes which exist in the blood of patients with intermittent fever. Of those parasites which remain in the human blood the male ones (microgametocytes) soon perish, the females (macrogametocytes) persist for some long time, and perhaps at last acquire the capacity of increasing by schizogony. They might thus form merozoites which behave in the body as if they had proceeded from ordinary schizonts (fig. 80, 13c-17c). If their number increases sufficiently, in course of time the patient, who was apparently recovering, has a new series of fever attacks, or relapses, without there having been a new infection. This is the view of Schaudinn, who from researches of his own concluded that relapses were brought about by a sort of parthenogenetic reproduction of macrogametocytes. R. Ross, on the contrary, believes that in the relatively healthy periods the number of parasites in the blood falls below that necessary to provoke febrile symptoms; relapses then result merely from increase in the numbers of the parasites present in the individual. Ross’s view is now generally accepted.

If the gametocytes, which are globular, or in the pernicious or malignant tertian parasite crescentic (fig. 81), gain access to the intestine of an Anopheline,[199] they mature. The macrogametocytes extrude a part of their nuclear substance (fig. 80, 13a, 14a) and thereby become females or macrogametes. The microgametocytes, on the other hand, undergo repeated nuclear division, preparation for this being made apparently whilst in the blood of man. This results in the formation of threadlike bodies which move like flagella and finally detach themselves from the residual body (fig. 80, 13b, 14b). These are the males or microgametes[200] (fig. 80, 15b).

[199] Schizonts ingested about the same time perish in the intestine of the mosquito.

[200] If the microgametocytes are sufficiently mature the formation of microgametes occurs in the blood of man as soon as it is taken from the blood-vessel and has been cooled and diluted. Such a stage is called a Polymitus form, and the process has been called “exflagellation.”

Copulation takes place in the stomach of the Anopheline (fig. 80, 16). A microgamete penetrates a macrogamete and coalesces with it. The fertilized females elongate very soon and are called oökinetes or “vermicules” (figs. 80, 17; 82). They penetrate the walls of the stomach, pierce the epithelium (fig. 80, 18, 19), and remain lying between it and the superficial stratum (tunica elastico-muscularis). Then they become rounded and gradually develop into cysts which grow larger and are finally visible to the naked eye, being called oöcysts (figs. 80, 20-24; 83). Their size at the beginning is about 5 µ, the maximum that they attain is 60 µ, only exceptionally are they larger.

The sporulation (figs. 80, 21-25; 84), which now follows, begins with repeated multiple fission of the nucleus. Long before the definitive number of nuclei, which varies with the individual, is attained the protoplasm, according to Grassi, begins to segment around the individual large nuclei but without separating completely into cell areas. According to Schaudinn, however, there is a condensation of the outstanding protoplasmic strands. It is certain that the number of nuclei increases with simultaneous decrease in size. They soon appear on the surface of the strands or sporoblasts, surround themselves with some cytoplasm and then elongate (fig. 84). In this manner the sporozoites are formed and break away from the unused remains of the cytoplasmic strands of the sporoblasts (fig. 80, 26). The number of the sporozoites in an oöcyst varies from several hundreds to ten thousand.

The sporulation is influenced in its duration by the external temperature (Grassi, Jansci, Schoo). In the tertian parasite it takes place quickest at a temperature of 25° to 30° C. and takes eight to nine days. A temperature a few degrees lower has a retarding effect (eighteen to nineteen days at 18° to 20° C). A still lower one has a restraining or even destructive effect. Temperatures over 35° C. also exercise a harmful effect. The malignant tertian parasite seems to need a somewhat higher temperature and the quartan parasite a lower one.

The sporozoites of the various malarial parasites show no specific differences. They were stated by Schaudinn to occur in three forms, and these were described as indifferent (neuter), female and male. There is, however, little or no evidence for this hypothetical differentiation. The last were said to perish prematurely, that is, in the oöcyst. The others after the rupture of the oöcysts enter the body cavity of the Anophelines, whence they are carried along in the course of the blood. Finally they penetrate the salivary glands (fig. 80, 27) probably by their own activity, break through their epithelia and accumulate in the salivary duct (fig. 80, 27). At the next bite by the mosquito they are transmitted to the blood-vessels of man.

THE SPECIES OF MALARIAL PARASITES OF MAN.

In view of the differences in opinion regarding “species” and “varieties,” the dispute whether the malarial parasites of man represent one species with several varieties, or several species is almost superfluous. If necessary two genera may be distinguished.

The parasites of the tertian and quartan fever are alike in that their gametocytes have a rounded shape (figs. 80, 12, 13), whilst the corresponding stages of the pernicious or malignant tertian parasites are crescentic (figs. 81, 88). These differences are used by some writers as the distinguishing characteristic of two genera: Plasmodium, Marchiafava and Celli, 1885, for the first mentioned species; Laverania, Grassi and Feletti, 1889, for the pernicious or malignant tertian parasite. Whether there is a genuine quotidian fever and accordingly a special quotidian parasite is still disputed.

These parasites are treated in practical detail in Stephens and Christophers’ “Practical Study of Malaria,” 3rd edition, 1908.

*Plasmodium vivax*, Grassi and Feletti, 1890.

Syn.: Hæmamœba vivax, Grassi and Feletti, 1890; Plasmodium malariæ var. tertianæ, Celli and Sanfelice, 1891; Hæmamœba laverani var. tertiana, Labbé, 1894; *Hæmosporidium tertianum*, Lewkowitz, 1897; Plasmodium malariæ tertianum, Labbé, 1899: Hæmamœba malariæ var. magna, Laveran, 1900, p.p.; Hæmamœba malariæ var. tertianæ, Laveran, 1901.

This species, P. vivax,[201] is the causal agent of the simple or spring tertian fever and is, therefore, named directly the tertian or benign tertian parasite (figs. 80, 3-8; 85). During the afebrile period in the patient, the young trophozoites or amœbulæ appear on or in the red blood corpuscles as pale bodies of 1·5 µ to 2 µ diameter which at first show only slow amœboid movements. Their nucleus is difficult to recognize in the early stage. Soon the food vacuole is formed and this grows concomitantly with the trophozoite and the parasite has a ring-like appearance. Afterwards the vacuole diminishes, and at this period the first brownish melanin granule appears. From this time the activity and number of the pigment granules increase with continuous growth. When the parasite has grown to about one-third the diameter of the erythrocyte the latter shows characteristic red Schüffner’s dots or “fine stippling,” after staining with Romanowsky’s solution. Later, after about twenty-four hours, the blood corpuscles begin to grow pale, then to increase in size, and after thirty-six hours, that is, about twelve hours before the next attack of fever, schizogony of the parasite is initiated by the division of the nucleus. The parasite at this time occupies half to two-thirds of the enlarged blood corpuscle. The daughter nuclei continue dividing until sixteen, and occasionally twenty-four, daughter nuclei are produced. The pigment which, up till now lies nearer the periphery, moves to the middle, while the nuclei lie nearer the surface.

[201] See Schaudinn, F. (1902), Arb. a. d. kaiserl. Gesundheits., xix, pp. 169–250, 3 plates.

Around each nucleus a portion of cytoplasm collects and thus young merozoites are produced. These separate from each other and from the little residual masses[202] which contain the melanin and pass from the blood corpuscles, which now can hardly be recognized, to the blood plasma, where they soon attack new erythrocytes.

[202] The pigment masses (melanin or hæmozoin) are taken up by the leucocytes, particularly the mononuclear ones, and are carried especially to the spleen, and also to the liver and the bone-marrow. From this circumstance arises the well-known pigmentation of the spleen in persons who have suffered from malaria.

The migration of the merozoites initiates a new attack of fever and two groups of tertian parasites in the blood, differing in development by about twenty-four hours, are the conditions for febris tertiana duplex.

After a lengthy duration of fever the gametocytes (figs. 80, 9--12) appear. They are uninucleate. The microgametocytes are about the size of fully developed schizonts, the macrogametocytes are somewhat larger. Their further development takes place in Anophelines.

The chief distinctive characteristics of the simple tertian parasite, as seen in infected blood, are:--(1) The infected red-cell is usually enlarged; (2) the presence of fine red granules known as Schüffner’s dots in the red blood corpuscles, after Romanowsky staining; (3) the fragile appearance of the parasite compared with other species. Large forms are pigmented, irregular and “flimsy-looking,” sometimes appearing to consist of separate parts. Irregularity of contour is common.

Ahmed Emin[203] (1914) has described a small variety of P. vivax.

[203] Bull. Soc. Path. Exot., vii, p. 385.

*Plasmodium malariæ*, Laveran.

Syn.: Oscillaria malariæ, Laveran, p.p., 1883; Hæmamœba malariæ, Gr. et Fel., 1890; Plasmodium malariæ var. quartanæ, Celli et Sanfel., 1891; Hæmamœba laverani var. quartana, Labbé, 1894; Hæmosporidium quartanæ, Lewkowitz, 1897; Plasmodium malariæ quartanum, Labbé, 1899; Plasmodium golgii, Sambon, 1902; Laverania malariæ, Jancso, 1905 nec Grassi et Fel. 1890; Hæmomœba malariæ var. quartanæ; Lav., 1901.

Plasmodium malariæ is the parasite of quartan malaria (fig. 86). The trophozoites of the quartan parasite differ from the corresponding stages of the tertian parasite in that their motility is less and soon ceases. They differ also in their slower growth, by the early disappearance of the food vacuole, by the more marked formation of the dark brown pigment, and by the fact that the red blood corpuscles attacked are not altered either in colour or size.

When the parasites have grown almost to the size of the erythrocytes schizogony occurs. The pigment granules arrange themselves in lines radiating towards the centre and the merozoites are also radially disposed in groups of 6, 8, 10 or even 12, but are often arranged less regularly. The whole development, growth and schizogony, occupies seventy-two hours.

The appearance of quartana duplex or triplex is conditional on the presence in the blood of the patient of two or three groups of Plasmodia differing in their development by twenty-four hours.

The chief distinctive characters of the quartan parasite are: (1) The erythrocyte is unchanged in size; (2) the rings are compact and show pigment early; in the larger forms the chromatin is dense and relatively plentiful; (3) the pigment, which is relatively well-marked, may be arranged at the periphery.

*Laverania malariæ*, Grassi and Feletti, 1890 = *Plasmodium falciparum*, Welch, 1897.

Syn.: Plasmodium malariæ var. quotidianæ, Celli et Sanf., 1891; Hæmamœba malariæ præcox, Gr. et Fel., 1892 (nec H. præcox, Gr. et Fel., 1890); Hæmamœba laverani, Labbé, 1894; Hæmatozoön falciparum, Welch, 1897; Hæmosporidium undecimanæ and H. sedecimanæ and H. vigesimo-tertianæ, Lewkowitz, 1897; Hæmamœba malariæ parva, Lav., 1900; Plasmodium præcox, Dofl., 1901; Plasmodium immaculatum, Schaud., 1902; Plasmodium falciparum, Blanch., 1905.

The names most commonly used for the parasite of malignant tertian malaria are Plasmodium falciparum and Laverania malariæ.

The summer and autumn fever (febris æstivo-autumnalis), also called malignant tertian or sub-tertian, is caused by a malarial parasite which is distinguished by the small size of its schizont, while the gametocytes are crescentic (figs. 81, 88).

Most authors identify this kind of fever or the parasites which cause it (Laverania malariæ) with the pernicious malaria of the tropics. Ziemann, however, repeatedly has drawn attention to certain small but definite differences between the usual malignant tertian or pernicious parasites which occur in the tropics and the tropical parasites of some malarial districts, particularly of West Africa, and insists that at least two varieties or sub-species occur. Other investigators distinguish from this or these forms a quotidian parasite. On the other hand, the assertion is made that there are no specific differences, but that the malignant or pernicious tertian parasite which normally needs forty-eight hours for its development in the blood of man, can also develop in twenty-four hours. The establishment of the duration of the development is a matter of especial difficulty, because the stages of schizogony are far less numerous in the peripheral blood than in that of the internal organs. It is also stated that the tropical parasite very seldom forms crescentic but rather rounded gametocytes. According to such an observation the organism would belong to Plasmodium and not to Laverania. The question whether the tropical fevers are caused by two different parasites does not seem to be definitely settled.

The young trophozoite of the malignant, pernicious tertian, or sub-tertian parasite (fig. 87) are but slightly active and are very small, even after the formation of the comparatively large food vacuole, which makes the body appear annular (“signet ring” stage). Often two and even more parasites are found in one blood corpuscle.

Fully grown they only attain two-thirds or less of the diameter of the erythrocytes, which display an inclination to shrink and then appear darker than the normal (brass-coloured). In the early stage dots or stippling--sometimes called Maurer’s dots--appear on the blood corpuscles as in those attacked by the ordinary tertian parasite (Plasmodium vivax), but the Maurer’s dots are relatively coarse and few, and are not easily stained. These dots were first described by Stephens and Christophers in 1900, and subsequently by Maurer in 1902.

About thirty hours after the entrance into the blood corpuscles, the parasites are rarely found in the peripheral blood, but they are present in the internal organs, and especially in the spleen. The schizogony, which now begins in the internal organs, proceeds on the same lines as that of the quartan parasite, that is, usually with the merozoites radially arranged around a central agglomeration of dark brown pigment.

The number of merozoites formed is quoted differently, e.g., 8 to 24, on an average 12 to 16. However, according to the recent cultural researches of J. G. and D. Thomson[204] (1913) the number of merozoites of P. falciparum is 32. D. Thomson, from examination of spleen smears at autopsy, also concludes that the number of merozoites may reach 32. During their formation the blood corpuscle which is attacked gets paler and disintegrates.

[204] Proc. Roy. Soc., B, lxxxvii, p. 77.

The gametocytes which finally appear are attenuated, curved bodies, rounded at each end and known as crescents (figs. 81, 88), and are provided with a nucleus and with coarse pigment masses. In the males the pigment is more scattered than in the females, where it is around the nucleus. Their length is 9 µ to 14 µ, and their breadth is 2 µ to 3 µ. At first they are still in the pale blood corpuscles, later they free themselves and are found in numbers in the peripheral blood in cases of pernicious malaria of Southern Europe and the tropics, while, on the other hand, they occur much more rarely in the peripheral blood in West African malignant tertian. Their further development takes place under the same conditions as in the other malarial parasites.

D. Thomson (1914),[205] from studies of autopsy smears, has shown that crescents develop chiefly in the bone-marrow and spleen, and take about ten days to grow into the adult state in the internal organs. He believes that crescents are produced from ordinary asexual spores. Quinine, he states, has no direct destructive action on crescents, but it destroys the asexual source of supply.

[205] Annals Trop. Med. and Parasitol., viii, p. 85.

The sporozoites of Laverania malariæ (P. falciparum) are represented in fig. 89.

The principal distinctive characters of the malignant tertian parasite are: (1) The ring forms are very small, occasionally bacilliform, and may be marginal (“accolé” of Laveran); (2) the larger trophozoites are often ovoid, and about one-third or one-half of the erythrocyte in size; (3) the infected red cells sometimes show coarse stippling (Maurer’s dots); (4) the gametocytes, or sexual forms, are crescentic in shape.

J. W. W. Stephens (1914) has described a new malarial parasite of man; it is called Plasmodium tenue. It is very amœboid, with scanty cytoplasm and much chromatin, sometimes rod-like or irregular. The parasite was described from a blood-smear of an Indian child. The creation of a new species for this parasite has been criticized by Balfour and Wenyon, and by Craig.

*Plasmodium relictum*, Sergent, 1907.

Syn.: Plasmodium præcox, Grassi and Feletti, 1890; Plasmodium danilewskyi, Gr. et Fel., 1890; Hæmamœba relicta, Gr. et Fel., 1891; Proteosoma grassii, Labbé, 1894.

Hæmamœboid, pigment-producing, malarial parasites are often found in birds. Like the human malarial parasites they have been variously named. Labbé created the genus Proteosoma for them, and this name is still often used as a distinctive one unofficially. The correct name is stated to be either Plasmodium relictum or P. præcox, or possibly even P. danilewskyi, assuming that there is only one species. The nomenclature of the malarial parasites is most confused. The avian malarial parasites are transmitted by Culicine mosquitoes.

The organism was discovered by Grassi in the blood of birds in Italy, and causes a fatal disease in partridges in Hungary. Sparrows are affected in India, and it was this Plasmodium in which Ross first traced the development of a malarial parasite in a mosquito. The parasite may be transmitted from bird to bird by blood-inoculation, canaries being very susceptible.

The principal stages of the avian plasmodium closely resemble those of the malarial parasites of man. In its earliest stage P. relictum is unpigmented, but soon the trophozoite grows and becomes pigmented, meanwhile displacing the nucleus of the avian red-blood corpuscle, a characteristic feature, distinguishing it from Halteridium. Schizonts are formed, each of which gives rise to about nine merozoites in the circulating blood. Sexual forms or gametocytes also occur in the blood. These develop in Culex fatigans, C. pipiens and C. nemorosus. Oökinetes or vermicules are formed in twelve to fifteen hours in the stomach of the mosquito, and in one to two days well-developed round oöcysts may be seen. In three to four days sporoblasts have formed within the oöcysts and young sporozoites begin to develop. In nine to ten days the oöcysts are mature, being filled with sporozoites. The oöcysts then burst and the sporozoites travel through the thoracic muscles to the salivary glands of the Culicine.

Neumann, experimenting with canaries, found that Stegomyia fasciata could transmit the infection, but less efficiently than species of Culex.

THE CULTIVATION OF MALARIAL PARASITES.

The successful cultivation of malarial parasites in vitro was first recorded by C. C. Bass and by Bass and Johns (1912).[206] Since then, J. G. and D. Thomson,[207] and McLellan (1912–13), Ziemann[208] and others have repeated the experiments.

[206] Journ. Exptl. Med., xvi, p. 567.

[207] Annals Trop. Med. and Parasitol., vi, p. 449; vii, pp. 153, 509.

[208] Trans. Soc. Trop. Med. and Hyg., vi, p. 220.

DIFFERENTIAL CHARACTERS OF THE HUMAN MALARIAL PARASITES.

======================================================================= | | |Laverania malariæ Character | _Plasmodium |Plasmodium vivax| Plasmodium | malariæ | (Benign tertian) | falciparum_ | (Quartan) | |(Malignant tertian) -------------+------------------+------------------+------------------- Schizogony |Complete in |Complete in forty-|Complete in forty- | seventy-two | eight hours | eight hours | hours | | or less -------------+------------------+------------------+------------------- Trophozoite |Smaller than _P. |Young trophozoite |Young trophozoite | vivax_larger than| large. | small | L. malariæ | | |Pseudopodia not |Long pseudopodia | | marked or long | | -------------+------------------+------------------+------------------- Movements |Rather slow in |Active amœboid |Sometimes actively | immature forms | movements | motile -------------+------------------+------------------+------------------- Pigment |Coarse granules, |Fine granules, |Granules fine and | peripherally | with active | scanty, movement | arranged, little | movement | oscillatory | movement | | -------------+------------------+------------------+------------------- Schizont |Smaller than red |Larger than red |Smaller than red | corpuscle | blood corpuscle | corpuscle -------------+------------------+------------------+------------------- Merozoites |6 to 12 forming |15 to 20 regularly|8 to 32 (according | rosette | arranged | to different | | | authors) arranged | | | irregularly -------------+------------------+------------------+------------------- Gametocytes |Spherical |Spherical |Crescentic -------------+------------------+------------------+------------------- Distribution |About equal number|Larger numbers in |Scanty in periph- of | in peripheral and| visceral blood | eral blood com- parasites in| visceral blood | | pared with the vertebrate | | | enormous numbers host | | | in the internal | | | organs. The latter | | | part of the cycle | | | (schizogony) may | | | occur in the in- | | | ternal organs only -------------+------------------+------------------+------------------- Alterations |Almost normal |Pale and |Corpuscle may be in | | hypertrophied. | shrunken and dark, erythrocytes| |Schüffner’s dots | or may be colour- | | seen in deeply | less. Maurer’s | | stained specimens| coarse dots some- | | | times seen -------------+------------------+------------------+-------------------

Essentially the method of cultivation, as used by Thomson, is as follows: 10 c.c. of infected blood are drawn from a vein and transferred to a sterile test tube, in which is a thick wire leading to the bottom of the tube. One-tenth of a cubic centimetre of a 50 per cent. aqueous solution of glucose or dextrose is placed in the test tube, preferably before adding the blood. The blood is defibrinated by stirring gently with the wire. When defibrination is complete the wire and the clot are removed, and the glucose-blood is transferred, in portions, to several smaller sterile tubes, each containing a column of blood about one inch in height. The tubes are plugged and capped and then transferred, standing upright, to an incubator kept at a temperature of 37° C. to 41° C. The blood corpuscles soon settle, leaving a column of serum at the top, to the extent of about half an inch in each tube. The leucocytes need not be removed by centrifugalization. J. G. Thomson (1913) and his collaborators did not find it necessary to destroy the complement in the serum, and they found that the malarial parasites developed at all levels in the column of corpuscles, and not merely on the surface layer of the corpuscles as first stated by Bass and Johns.

So far only the asexual generation of the malarial parasites has been grown in vitro. Thomson rarely observed hæmolysis in the cultures. Clumping of the malignant tertian parasites occurred. In cultures of the benign tertian parasite (Plasmodium vivax) clumping was not observed. J. G. and D. Thomson consider that this difference as regards clumping explains why only young forms of malignant tertian are found in peripheral blood, as the clumping tendency of the larger forms causes them to be arrested in the finer capillaries of the internal organs. It also explains the tendency to pernicious symptoms, such as coma, in malignant tertian malaria. Further it was found from cultures that P. falciparum was capable of producing thirty-two spores (merozoites) in maximum segmentation, while P. vivax produced sixteen spores (merozoites) as a rule, though the number might be greater than sixteen. (Quartan parasites produce eight spores or merozoites in schizogony.)

It may also be mentioned here that Babesia (Piroplasma) canis has been successfully cultivated in vitro by Bass’s method. This has been accomplished by Thomson and Fantham,[209] Ziemann, and Toyoda in 1913. J. G. Thomson and Fantham used the simplified Bass technique recorded above, namely, infected blood and glucose, incubating at 37° C. In one of the B. canis cultures, starting with heart blood of a dog containing corpuscles infected with one, two, or, exceptionally, four piroplasmata, Thomson and Fantham succeeded in obtaining a maximum of thirty-two merozoites in a corpuscle. The cultures are infective to dogs and sub-cultures have been obtained.

[209] Annals Trop. Med. and Parasitol., vii, p. 621.

Family. *Piroplasmidæ*, França.

The parasites included in this provisional family or group belong to the Hæmosporidia. They are minute organisms, sometimes amœboid, but usually possessing a definite form. They are endoglobular, being contained within mammalian red blood corpuscles, but they produce no pigment. The true Piroplasmata, belonging to the genus Babesia, destroy the host corpuscles, setting free the hæmoglobin, which is excreted by the kidneys of the cow, sheep, horse, dog, etc., acting as host. The disease produced, variously called piroplasmosis or babesiasis, is consequently characterized by a red coloration of the urine known as hæmoglobinuria, or popularly as “red-water.” One of the best known piroplasms is Piroplasma bigeminum or Babesia bovis (probably the latter name is correct), which is the causal agent of “Texas fever” or “red-water” in cattle and is spread by ticks.

Of recent years, researches on the morphology of these blood parasites has led to their separation into various genera and species. However, our knowledge is still very far from complete. The various genera recognized by França[210] (1909), and placed in a provisional family, Piroplasmidæ, may be listed, though further research may lead to emendations:--

[210] Arch. Inst. Bact. Camara Pestana, iii, p. 11.

(1) Babesia (Starcovici) or Piroplasma (Patton). Pyriform parasites, dividing by a special form of budding or gemmation with chromatin forking, as well as by direct binary fission. Parasitic in oxen, dogs, sheep, horses, etc.

(2) Theileria (Bettencourt, França and Borges). Rod-shaped and oval parasites occurring in cattle and deer. T. parva is the pathogenic agent of African East Coast fever in cattle.

(3) Nuttallia (França). Oval or pear-shaped parasites, with multiplication in the form of a cross. N. equi[211] (fig. 90) of equine “piroplasmosis” (nuttalliosis). N. herpestidis in a mongoose.

[211] Parasitology, v (1912), p. 65.

(4) Nicollia (Nuttall). Oval or pear-shaped parasites with characteristic nuclear dimorphism, and with quadruple division at first fan-like, then like a four-leaved clover. N. quadrigemina from the gondi.

(5) Smithia (França). Pear-shaped, single forms stretching across the blood corpuscle. Multiplication into four in the form of a cross. S. microti from Microtus arvalis, S. talpæ from the mole.

(6) Rossiella (Nuttall). This belongs to the family Piroplasmidæ of França. It is intracorpuscular and non-pigment forming, occurring singly, in pairs, or occasionally in fours. It is usually round and larger than Babesia. The parasite multiplies by binary fission. R. rossi in the jackal.

The genus Babesia is the best known and most important, and will be considered next.

Genus. *Babesia*, Starcovici, 1893.

Syn.: Pyrosoma, Smith and Kilborne, 1893; Apiosoma, Wandolleck, 1895; Piroplasma, W. H. Patton, 1895; Amœbosporidium, Bonome, 1895.

The organisms belonging to this genus are pyriform, round or amœboid. The characteristic mode of division is as follows: Just before division the parasite becomes amœboid and irregular in shape, (fig. 91, 1–5) with a compact nucleus. The latter gives off a nuclear bud. This nuclear bud divides into two by forking (fig. 91, 6, 7). The chromatin forks grow towards the surface of the body of the rounded parasite, and then two cytoplasmic buds grow out. The forking nuclear buds, which are *Y*-shaped, pass into the cytoplasmic outgrowths[212] (fig. 91, 8, 9). The buds gradually increase in size at the expense of the parent form until they become two pear-shaped parasites joined at their pointed ends. The connecting strand shrinks and the two daughter forms separate (fig. 91, 10–14). The pyriform parasites after having exhausted the blood corpuscle escape from it (fig. 91, 15), and seek out fresh host corpuscles, entering by the rounded, blunt end (fig. 91, 1). It is the pyriform phase of the parasite which penetrates red blood corpuscles, not rounded forms, which die if set free. The pyriform parasite, however, becomes rounded (fig. 91, 2, 3), soon after its entry into a fresh host cell. This interesting mode of division by gemmation and chromatin forking has been made diagnostic of the genus Babesia by Nuttall.[213] Rounded forms of Babesia divide by binary fission, and this direct method can also be adopted by the other forms of Babesia.

[212] Nuttall and Graham-Smith, Journ. Hyg., vii, p. 232.

[213] “Piroplasmosis,” Herter Lectures, Parasitology, vi, p. 302.

The distribution of the chromatin in the pear-shaped Babesia, as seen in B. canis and B. bovis, is interesting. The main nuclear body consists of a karyosome surrounded by a clear area. There is also a loose (chromidial) mass of chromatin representing the remains of the chromatin forks seen during the formation of the parasite as a daughter form by gemmation. Occasionally there is a small dot or point, the so-called “blepharoplast” of Schaudinn and Lühe. This minute dot is not a flagellate blepharoplast, for there is no flagellate stage in the life-history of Babesia. These nuclear phenomena have been described by Nuttall and Graham-Smith and Christophers (1907)[214] for B. canis, by Fantham (1907)[215] for B. bovis, and by Thomson and Fantham (1913) from glucose-blood cultures of B. canis.

[214] Sci. Mems. Govt. India, No. 29.

[215] Quart. Journ. Microsc. Sci., li, p. 297.

Babesia are tick borne, as was first shown by Smith and Kilborne (1893). The developmental cycle in the tick is incompletely known. The best accounts are those of Christophers (1907)[216] for B. canis and Koch (1906) for B. bovis, and these accounts are supplementary. The principal stages, so far as known, may be summarized thus:--

[216] Sci. Mems. Govt. India, No. 29.

(1) The piroplasms taken by the tick in feeding on blood pass into the tick’s stomach. The pyriform parasites, which alone are capable of further development, are set free from the blood corpuscles. In about twelve to eighteen hours they become amœboid, sending out long, stiff, slender, pointed pseudopodia. The nucleus of each parasite divides unequally into two. Similar forms have been obtained in cultures. These stellate forms may be gametes, and according to Koch fuse in pairs.

(2) A spherical stage follows, possibly representing the zygote. This grows, and a uninucleate globular mass results. This form is found in large numbers on the third day, according to the observations of Koch.

(3) A club-shaped organism is next formed. This may represent an oökinete stage. The club-shaped bodies are motile and gregarine-like, and are about four times the size of the blood forms. These club-shaped bodies and subsequent stages were described by Christophers in the development of B. canis in the dog-tick, Rhipicephalus sanguineus.

(4) The club-shaped bodies pass from the gut of the tick into the ovary, and so get into the ova. There they become globular, and later are found in the cells of the developing tick-embryo. The parasites are, then, transmitted hereditarily. Similar globular bodies are found in the tissue cells of the body of tick nymphs which have taken up piroplasms. The globular stage was called the “zygote” by Christophers, but it may correspond to the oöcyst of Plasmodia.

(5) The globular body divides into a number of “sporoblasts,” which become scattered through the tissues of the larval or nymphal tick, as the case may be.

(6) The sporoblasts themselves divide into a large number of sporozoites, which are small uninucleate bodies, somewhat resembling blood piroplasms. The sporozoites collect in the salivary glands of the tick. They are inoculated into the vertebrate when the tick next feeds.

The chief species of Babesia and their pathogenic importance may be listed thus:--

(1) Babesia bovis (Babes) produces infectious hæmoglobinuria of cattle in Europe and North Africa. It is transmitted by Ixodes ricinus. A similar parasite also occurs in deer.

(2) Babesia bigemina (Smith and Kilborne) produces Texas fever, tristeza, or red-water in cattle in North and South America, South Africa and Australia. It is transmitted by Boöphilus annulatus in North America, by B. australis in Australia, South America, and the Philippines, and by B. decoloratus in South Africa.

The parasite is from 2 µ to 4 µ long, and from 1·5 µ to 2 µ broad.

Babesia bigemina may be the same parasite as B. bovis.

(3) Babesia divergens (MacFadyean and Stockman) is a small parasite. It is found in cattle suffering from red-water in Norway, Germany, Russia, Hungary, Ireland, Finland, and France, and is transmitted by Ixodes ricinus.

(4) Babesia canis (Piana and Galli-Valerio) gives rise to malignant jaundice or infectious icterus in dogs in Southern Europe, India, and other parts of Asia and North Africa, where it is transmitted by Rhipicephalus sanguineus. In Africa generally, especially South Africa, the disease is transmitted by Hæmaphysalis leachi. Babesia canis varies from 0·7 µ to 5 µ, the size depending partly on the number of parasites within the corpuscle. It averages about 3 µ. It has been cultivated in Bass’ medium (glucose and infected blood), see p. 172.

In India Piroplasma gibsoni (Patton) infects hunt dogs and jackals. It is annular or oval in shape.

(5) Babesia ovis (Babes) produces “Carceag,” a disease of sheep in Roumania, the Balkan Peninsula, Italy, and Transcaucasia. It varies in size from 1 µ to 3 µ. It is transmitted by Rhipicephalus bursa. The parasite has recently been recorded from Rhodesia.

(6) Babesia caballi (Nuttall and Strickland) causes “biliary fever” in equines. The parasite occurs in Russia, Roumania, and Transcaucasia. It varies in size from 1 µ to 2 µ. It is transmitted by Dermacentor reticulatus.

It should be mentioned that Nuttallia equi also causes “piroplasmosis” in equines, with symptoms of hæmoglobinuria and jaundice in Italy, Sardinia, many parts of Africa, Transcaucasia, India, and Brazil. In Africa it is transmitted by Rhipicephalus evertsi. It has been shown experimentally that a horse recovered from Babesia caballi was susceptible to the inoculation of Nuttallia equi blood.

(7) Babesia pitheci (P. H. Ross) was found in a monkey, Cercopithecus sp., in Uganda. The pear-shaped forms measure 1·5 µ by 2·5 µ.

(8) Babesia muris (Fantham)[217] was found in white rats. The pyriform parasites are 2 µ to 3 µ long and 1 µ to 1·5 µ broad; oval forms are 0·5 to 1·5 µ diameter.

[217] Quart. Journ. Microsc. Sci., 1, p. 493.

The usual symptoms of babesiasis (piroplasmosis) are high fever, loss of appetite, hæmoglobinuria, icterus, anæmia, paralysis, and death in about a week in acute cases. In chronic cases there is anæmia, and hæmoglobinuria is less marked. When animals recover, there are still some piroplasms left in the blood. “Recovered” or “salted” animals are not susceptible to reinfection, but ticks feeding on them acquire piroplasms, and are a source of danger to freshly imported animals.

Treatment.--Trypan-blue is the best drug, as shown by Nuttall and Hadwen[218] (1909). It should be administered intravenously in 1 to 1·5 per cent. aqueous solution. A dose of 5 to 10 c.c. is curative for dogs, one of 100 to 150 c.c. for horses and cattle. Unfortunately, the tissues are coloured blue by the drug. The “salted” animals, after trypan-blue treatment, still harbour the parasites in their blood for years.

[218] Parasitology, ii, p. 156.

Genus. *Theileria*, Bettencourt, França and Borges, 1907.

The organisms belonging to this genus are rod-like or bacilliform, and coccoid or round.

The best known of the species of Theileria is T. parva, the pathogenic agent of East Coast fever or Rhodesian fever in cattle in Africa.

*Theileria parva*, Theiler, 1903.

Syn.: Piroplasma parvum.

In the blood corpuscles of infected cattle minute rod-like and oval parasites are seen. Some are comma shaped and others are clubbed (fig. 92, 1–12). The rod-like forms measure 1 µ to 3 µ in length by 0·5 µ in breadth; the oval forms are 0·7 µ to 1·5 µ in diameter. The intracorpuscular parasites are said by R. Gonder (1910) to be gametocytes, the rod-like forms being thought to be males, the oval forms to be females. Free parasites are practically never seen in the blood. It is known that it is impossible to produce the disease in a healthy animal by blood inoculation, but only by intraperitoneal transplantation of large pieces of infected spleen (Meyer). There may be as many as eight parasites in a corpuscle. The chromatin is usually at one end of the organism. In some parasites the appearance of the chromatin suggests division, but such division, if it takes place, must be very slow, as it has not been actually seen in progress. The red blood corpuscles appear merely to act as vehicles for the parasites (Nuttall, Fantham, and Porter).[219]

[219] Parasitology, ii, p. 325; iii, p. 117.

In the internal organs, especially the lymphatic glands, spleen and bone-marrow, are found multinucleate bodies known as Koch’s blue bodies (fig. 92, 13–18). These are schizonts, according to Gonder.[220] The actual Koch’s blue bodies are said to be extracellular, but similar multinucleate bodies, schizonts, occur in lymphocytes. The schizonts divide and the merozoites resulting probably invade the red blood corpuscles in the internal organs. Gonder considers that the sporozoites injected by the tick collect in the spleen and lymphatic glands, penetrate the lymphocytes and give rise to the schizonts.

[220] Zeitschr. f. Infekt. paras. Krankh. u. Hyg. d. Haustiere, viii, p. 406.

Gonder has studied the cycle of T. parva in the tick. He states that the gametocytes leave the host corpuscles and give rise to gametes, then conjugation occurs producing zygotes. The zygotes are then said to become active to form ookinetes, and to enter the salivary glands of the tick. Multiplication is said to occur therein, producing a swarm of sporozoites. This work needs confirmation.

T. parva is transmitted by Rhipicephalus appendiculatus, R. simus, R. evertsi, R. nitens, and R. capensis. The parasites are not hereditarily transmitted in Rhipicephalus, but when taken by the transmitter at one stage of its development the tick is infective in its next stage (e.g., if the larva becomes infected, then the nymph is infective; if the nymph becomes infected, then the adult is infective).

An animal recovered from Theileria parva is incapable of infecting ticks, but few animals recover from East Coast fever. Animals suffering therefrom do not show hæmoglobinuria.

*Theileria mutans*, Theiler, 1907·

Syn.: Piroplasma mutans.

This is transmissible experimentally by blood inoculation. It occurs in cattle in South Africa and Madagascar and is apparently non-pathogenic. No Koch’s blue bodies are formed. It is transmitted by ticks.

Theileria annulata (Dschunkowsky and Luhs) occurs in cattle in Transcaucasia.

A Theileria (T. stordii) has been found in a gazelle (França, 1912).

Genus. *Anaplasma*, Theiler, 1910.

This genus[221] may be mentioned here. The organisms included therein are, according to Theiler, coccus-like, consisting of chromatin, and are devoid of cytoplasm. They occur in the red blood corpuscles of cattle, causing a disease characterized by destruction of red cells, fever and anæmia, but with yellow urine. The disease is tick transmitted. The bodies now called Anaplasma marginale were formerly described as marginal points. They multiply by simple fission. They are said by Theiler to cause gall-sickness in cattle in South Africa. Some authors doubt whether these bodies are organismal.

[221] Bull. Soc. Path. Exot., iii, p. 135.

Genus. *Paraplasma*, Seidelin, 1911.

Under this generic name Seidelin described certain bodies found by him in cases of yellow fever in 1909. The type species is P. flavigenum,[222] and is claimed by Seidelin to be the causal agent of yellow fever.

[222] Yellow Fever Bulletin, i, p. 251.

Paraplasma flavigenum occurs in the early days of the disease as small chromatin granules with or without a faint trace of cytoplasm. The bodies are usually intracorpuscular. Also, somewhat larger forms, with distinct cytoplasm, are seen in small numbers. During the later days of the disease still larger forms are found, and these occur also in sections of organs (e.g., kidney) made post-mortem. Some of these larger forms are perhaps schizonts. In the second period of the disease possible micro- and macro-gametes may be found, some of which are extracorpuscular. Some small free bodies have been seen. Recently schizogony has been stated to occur in the lungs, and it is said that guinea-pigs can be inoculated with Paraplasma flavigenum, and show yellow pigment in the spleen.

Seidelin places Paraplasma in the Babesiidæ, with resemblances more particularly to Theileria. V. Schilling-Torgau and Agramonte have criticized these findings; the former considers them to be the resultant of certain blood conditions.

P. subflavigenum was found by Seidelin in 1912 in a man suffering from an unclassified fever in Mexico.

Further, it is now known that a Paraplasma occurs naturally in guinea-pigs. More researches are needed on these matters, as some writers (e.g., Wenyon and Low) claim that the bodies are not organismal.

-------------------------------------------------------------------- |Paraplasma flavigenum.--The Yellow Fever Commission (West Africa) | |in their third report, dated 1915, have come to the conclusion that | |there is no evidence that the bodies termed Paraplasma flavigenum | |are of protozoal nature or that they are the causal agents of yellow| |fever. | --------------------------------------------------------------------

Sub-class. NEOSPORIDIA, Schaudinn.

Sporozoa in which growth and spore formation usually go on together.

Order. *Myxosporidia*, Bütschli.

These parasites, which were discovered by Johannes Müller (1841), live principally in fishes, and occasionally cause destructive epizoötics amongst their hosts. Müller first observed them in the form of whitish-yellow pustules on the skin or on the gills of various fishes. These pustules contained masses of small shell-covered bodies with or without tails (“psorosperms,” see fig. 93). Similar bodies were also found in the air bladders of certain fish. Creplin (1842) demonstrated the resemblance of the cysts (“psorosperm tubes”) harbouring the psorosperms to the “pseudonavicella-cysts” of a gregarine, as described by v. Siebold. Dujardin (1845) considered that there was possibly some connection between the protoplasmic “psorosperm tubes” and the spores they contained, and the developmental stages of monocystid gregarines from the vesiculæ seminales of earth-worms. The relationship of the “fish psorosperms” was placed on a firmer basis by Leydig (1851) and Lieberkühn. The former found numerous forms in marine fish, and he discovered in species which live free in the gall bladder of cartilaginous fishes that the psorosperms originated in a manner similar to the gregarines. Lieberkühn (1854) studied the Myxosporidia in the bladder of the pike (fig. 93, a, b, d), and observed their amœboid movements, as well as the formation of the spores, from each of which a small amœboid body escaped, a discovery that was confirmed by Balbiani. The same author also found that spiral filaments were enclosed in the so-called polar body, i.e., the polar capsule of the psorosperm spores, and that these could be protruded (fig. 93, d, and fig. 95).

The term Myxosporidia, which at the present day is universally applied to the “psorosperm tubes,” was introduced by Bütschli in 1881, who studied not only the structure and development of the spores, but also the protoplasmic body of the parasites (fig. 96), and confirmed the occurrence of numerous nuclei. Many authors have made important additions to our knowledge of the Myxosporidia: Perugia, Thélohan, Mingazzini, L. Pfeiffer, L. Cohn, Doflein, Mercier, Schröder and Auerbach; while the presence of this parasite outside the class of fishes has become known through Lutz, Laveran, and others. The species causing disease in fishes have been described by Ludwig, Railliet, Weltner, L. Pfeiffer, Zschokke, Hofer, Doflein, Gurley, Plehn, Schuberg, Fantham and Porter. With regard to classification the works of Thélohan (1895) and Gurley (1894) may be mentioned.

The Myxosporidia live either free on the epithelial surface of hollow organs (gall or urinary bladder, renal tubules, but never in the intestine), or are enclosed in the tissues of their host. The gills and muscular system are their favourite habitat, but other tissues or organs may be attacked. Species of Myxosporidia are also known from Amphibia, Reptilia, and a few invertebrates.

The free forms, which are often amœboid (fig. 96), move by the aid of variously shaped pseudopodia, have a constant form, or may exhibit contractions of the body. The tissue parasites often reach a considerable size, so that the integument of the host forms protuberances over them. They are of a roundish or irregular shape. Frequently they are enveloped in a connective tissue covering formed by the host.

The protoplasmic body in the trophic phase (fig. 96) shows a distinct ectoplasm which is finely granular or sometimes striated, and an endoplasm which is coarsely granular and contains many nuclei as well as cell inclusions, such as crystals, pigment grains and fat globules. The nuclei originate by division from the primitive nucleus of the amœboid germ that issues from the spore. This amœbula may or may not live intra-cellularly during the early stages of its existence.

The multinucleate trophozoite of a Myxosporidian forms spores in its endoplasm practically throughout its whole period of growth (fig. 96). Vegetative reproduction by a process of external budding or plasmotomy may also occur, as in Myxidium lieberkühni from the urinary bladder of the pike.

The myxosporidian trophozoite may produce two spores within itself, when it is placed in the sub-order Disporea, or it may produce numerous spores, which is characteristic of the sub-order, Polysporea. The phenomenon of spore formation is not simple (fig. 97), and the spore itself is surrounded by a bivalved shell or sporocyst and contains polar capsules in addition to the amœboid germ (fig. 97, G, H). The valves of the sporocyst and the polar capsules are really differentiated nucleate cells, so that each spore is an aggregate of cells rather than one cell, though only a single amœbula issues from a spore. The accounts of spore formation vary somewhat according to the different workers.

Spore formation is usually very complicated and there are differences of opinion as to the interpretation of various stages, particularly as to whether conjugation occurs therein. The process is initiated by the concentration of cytoplasm around one of the nuclei of the endoplasm, so that a small spherical mass or initial corpuscle is produced, the pansporoblast (Gurley) or primitive sphere (Thélohan). Some authors state that a pansporoblast really results from a conjugation of two initial corpuscles (fig. 97, A-D). Nuclear multiplication occurs within the pansporoblast (fig. 97, E), and sooner or later two multinucleate sporoblasts are formed within it (fig. 97, F). Each sporoblast gives rise to a single spore, which consists of a sporocyst or envelope composed of two valves each secreted by a cell, two polar capsules each secreted by a cell, and the sporoplasm or amœbula which becomes binucleate (fig. 97, G). During the process of spore formation (fig. 97) various vegetative and reduction nuclei may be produced, in addition to those which are essentially involved in spore formation, and the sporocyst cells may be developed early.

Each spore contains two (figs. 94, 95) or more polar capsules which are clearly visible in the fresh condition. Each polar capsule is a hollow, more or less pear-shaped body, secreted by a cell and having a well defined contour. Within it, a long, delicate, elastic filament, the polar filament, is formed, and lies spirally coiled in the polar capsule until just before the emergence of the amœbula from the spore (fig. 95). The polar filament is ejected, probably under the influence of the digestive juice, when the spore reaches a new host, and serves to anchor the spore to the tissue with which it is in contact, and thus allow of the emergence of the amœbula in a situation suitable for its development. The polar capsule with its contained polar filament has been compared with the stinging cells or nematocysts of the Cœlentera, but it has a totally different function.

The spores fulfil the purpose of effecting transmission to other hosts. Infection occurs by the ingestion of the parasites per os after their escape by some means from their host. Thélohan and others have demonstrated that the valves of the spores soon open under the influence of the digestive juices, thus allowing the young myxosporidia to escape. Their further history is unknown; but it may be surmised that they either travel direct to the organs usually affected (gall bladder, urinary bladder), or are distributed in the body by means of the circulatory or lymphatic systems.

The Myxosporidia that invade tissues are often deadly to their hosts. They may be present in a state of “diffuse infiltration” when practically every organ of the body may be infected, as in barbel disease (due to Myxobolus pfeifferi). On the other hand, the parasites may be concentrated at one spot, when cysts, either large or small, are produced. Such cysts occur on the gills of many fishes. A few additional important pathogenic forms are Myxobolus cyprini, the excitant of “pockenkrankheit” of carp, and Lentospora cerebralis, parasitic in the skeleton of Salmonidæ and Gadidæ. The skeletons of the tail, fins and skull particularly are seats of infection, and from the skull the Lentospora can spread to the semicircular canals, resulting in loss of power to maintain its balance on the part of the fish. On this account the malady is termed “drehkrankheit.” Young fish are more particularly infected. Myxobolus neurobius infects the spinal cord and nerves of trout.

Myxosporidia are divided into two sub-orders--Disporea and Polysporea--according to whether they form only two or several spores during their growth. The former include two genera limited to fishes, which are easily distinguishable by the shape of the spores: Leptotheca, Thél., with a rounded spore, and Ceratomyxa, Thél., with a very elongate spore. The larger number of genera belong to the Polysporea, which are divided into three families:

(1) Amœboid germ with a vacuole {(a) With two polar capsules.-- the contents of which do { Myxidiidæ. not stain with iodine. {(b) With four polar capsules.-- Chloromyxidæ.

(2) Amœboid germ with a vacuole stainable with iodine. Spores with two polar capsules.--Myxobolidæ.

For further subdivisions the differences in the spores are principally utilized.

Order. *Microsporidia*, Balbiani.

These are the organisms discovered in the stickleback by Gluge in 1834, and in Coccus hesperidum by Leydig in 1853. They have since been found in numerous other arthropods, especially insects. They acquired particular importance when it was discovered that they were the cause of the “pébrine” disease (“gattina” of the Italians) which caused so much destruction amongst silkworms (Bombyx mori). Pasteur (1867–70) and especially Balbiani (1866) participated in the researches on Nosema bombycis, and it was the latter who classed the “pébrine bodies” or “psorospermia of the arthropoda” amongst the Sporozoa as Microsporidia (1882).[223] The complete life cycle of N. bombycis was described in 1909 by Stempell. The Microsporidia are not confined to insects and arachnoids, they are now known to occur also in crustacea, worms, bryozoa, fishes, amphibians and reptiles. Certain tumours in fishes, similar to those formed by many Myxosporidia, are produced by Microsporidia. Fantham and Porter found that Nosema apis was pathogenic to bees and other insects, and was the causal agent of the so-called “Isle of Wight” disease in bees[224] in Great Britain.

[223] C. R. Acad. Sci., Paris, xcv, p. 1168.

[224] Annals Trop. Med. and Parasitol., vi, pp. 145–214, 3 pls.

The Microsporidia, as their name implies, form minute spores which usually are oval or pear-shaped. Each spore contains a single polar capsule which is not easily visible in the fresh state (fig. 98, f) and a single amœboid germ issues from the spore (fig. 99, b).

The life cycle of Nosema apis, parasitic in bees, may be taken as an example of that of a microsporidian. The infection of the host is initiated by the ingestion of spores of N. apis in food or drink contaminated with the excrement of other infected bees. Under the influence of the digestive juice of the bee the spore-coat (sporocyst) softens, the polar filament is ejected and anchors the spore to the gut epithelium, and the minute amœbula contained in the spore emerges. The amœbula is capable of active amœboid movements (fig. 98, b) and so is termed the planont or wandering form (fig. 98, a). After a short time each planont penetrates between or into the cells of the epithelium of the gut, a few only passing through into the body cavity. Within the cells the amœbulæ become more or less rounded, lose their power of movement, and after a period of growth of the trophozoite (fig. 98, c) commence to divide actively, these dividing forms being known as meronts (fig. 98, d). Various forms of fission occur, and during this phase, termed merogony, the numbers of the parasite within the host are greatly increased, with concomitant destruction of the epithelium (fig. 98, e). After a time sporogony commences. The full-grown meront becomes successively the pansporoblast and sporoblast. Nuclear multiplication and differentiation ensue and five nuclei are ultimately produced. At the same time a sporocyst is secreted, and two vacuoles are produced within. One is the polar capsule, and within it the polar filament is differentiated; the other forms the posterior vacuole (fig. 98, g). Between the two vacuoles the body cytoplasm or sporoplasm forms a girdle-like mass. Of the nuclei, one regulates the polar capsule, two control the secretion of the sporocyst, and two remain in the sporoplasm. The polar capsule and polar filament are not usually visible in the fresh condition, but can be demonstrated by the use of various chemical reagents (fig. 100). The sporoplasm ultimately becomes the amœbula (fig. 98, g) which issues from the spore after the ejection of the polar filament.

A trophozoite (meront) of N. apis becomes a single pansporoblast which gives rise to one sporoblast producing one spore, and this procedure is characteristic of the genus Nosema. In other genera the trophozoite may form more than one pansporoblast and each pansporoblast may form a variable number of spores in different cases. Various attempts at classification have been based on these characteristics. It must suffice here to note that in the cases where the trophozoite becomes one pansporoblast, the latter can produce four spores in the genus Gurleya, eight spores in Thélohania and many spores in Pleistophora. In other cases, where the trophozoites give rise to many pansporoblasts, each of the latter may form many spores, as in the genus Glugea.

A few pathogenic microsporidian parasites other than N. apis may be mentioned. N. bombycis, causing pébrine in silkworms, may infect any or all the tissues of the host (fig. 99). The larvæ of the host, i.e., the “silkworms,” may become infected by eating food contaminated with spore-containing excrement of already infected silkworms. In cases of heavy infection the silkworm dies, but should the infection be less intense the larva becomes a pupa in which the parasite persists, so that the moth emerges from the cocoon already infected. Not only is the moth parasitized itself, but the Nosema reaches the generative organs of both sexes and penetrates the ovaries of the female, with the result that the ova are deposited infected. Such infected eggs are capable of developing, so that infection may be transmitted hereditarily as well as by the contaminative method. Infected eggs can be recognized by microscopic examination, as Pasteur showed, and thus preventive measures may be adopted.

A microsporidian parasite is known to occur on the roots of the spinal and cranial nerves of Lophius piscatorius, the angler fish. This parasite is variously referred to the genera Nosema and Glugea.

Thélohania contejeani, parasitic in the muscles of crayfish, is believed by some to be the causal agent of recent epizoötics among them, though others believe the disease to be really due to a bacillus. It may be that the one organism aids in the entry of the other into the host.

Order. *Actinomyxidia*, Stolč.

A brief mention may be made of the Actinomyxidia (fig. 101), which were first described by Stolč in 1899 as parasites of Oligochætes. They have also been investigated by Mrazek, and a detailed study of certain species was made by Caullery and Mesnil (1905). The trophozoite is small and amœboid. The spores are large, and exhibit tri-radiate symmetry. Spore formation is complicated and sexual processes occur therein. Many amœbulæ are set free from each spore.

Order. *Sarcosporidia*, Balbiani.

The first member of this group was discovered by Miescher in 1843. This author found white filaments running parallel with the direction of the fibres in the voluntary muscles of mice. They were visible to the naked eye, and proved to be cylindrical tubes tapering at each end. They were as long as the muscular fibres, were enveloped in a membrane, and contained innumerable elongate or kidney-shaped bodies and a smaller number of little spherical forms. Th. v. Hessling confirmed (1853) the occurrence of these “Miescher’s tubes” within the muscular fibres, this author having discovered the same structures in the heart muscles of deer, cattle, and sheep. Both investigators considered them to be pathological transformations of the muscles. v. Siebold, from his own experiences, regarded them as fungus-like entophytes.

Rainey (1858) discovered similar structures in the muscular system of pigs, and considered them to be early stages of Cysticercus cellulosæ, which error Leuckart rectified, simultaneously emphasizing their relationship with Myxosporidia. Both these authors found them in the muscular fibres, and both observed that they possessed a thick striated membrane. Manz (1867) published the results of more minute investigations on the structure and contents of the cylinders. This observer also recognized the disease in rabbits and attempted to cultivate the parasites. He also tried to induce experimental infection in guinea-pigs, rats, and mice, but the result was negative.

However, domestic and wild mammals are not the only hosts of Sarcosporidia; these parasites are also harboured by birds. Thus, according to Kühn, they are found in the domestic fowl; according to Rivolta in Turdus, Corvus, and other birds; according to Stiles in North American birds; while Fantham found Sarcosporidia in the African mouse-bird, Colius. Reptiles also are parasitized occasionally. Bertram found them in the gecko, Lühe in the wall-lizard. It was found also that the Sarcosporidia could develop not only in the muscles but also in the connective tissue. This led to the foundation of a new, but provisional, classification by Blanchard, using the generic name Miescheria for the parasites in the muscles and Balbiania for those in the connective tissue. Finally, Sarcosporidia have also been observed in man.

The relation of these parasites to certain diseases of domestic animals has been studied by veterinary surgeons. Sarcosporidia may cause fatal epizoötics among sheep.

There is still a wide field open for research in regard to the structure and development of these parasites, and the manner in which the hosts become infected.

The Sarcosporidia usually appear as elongate, cylindrical, or fusiform bodies, rounded at both extremities and of various lengths and breadths (fig. 102). In some species they may be from 16 mm. to 50 mm. long, as in the sheep and roebuck. These bodies are the so-called sarcocysts or Miescher’s tubes. They lie in transversely striated muscular fibres which they distend more or less. The forms found in the connective tissue are apparently parasites which originally inhabited the muscular fibres, and only on disintegration of the fibres reached the connective tissue, where they grow to large oval or globular bodies (fig. 105). The mammalian muscles usually infected are those of the œsophagus, larynx, diaphragm, body-wall, and the psoas muscles. The skeletal muscles may be affected in acute cases, as well as those of the tongue and eye. The heart muscles are sometimes parasitized.

In fresh material cut into thin slices the parasites are frequently recognizable, even with the naked eye, because of their yellowish-white colour. Under the microscope they appear to be coarsely granular (fig. 103). Beginners may find some difficulty in distinguishing them from other foreign bodies, such as dead and calcified encapsuled Trichinæ, or from Cysticerci that have died and become calcified in the early stages, more particularly as the Sarcosporidia also occasionally may become calcified.

The Sarcosporidia are always enveloped in a membrane, which is probably formed at an early stage. In a few cases it remains thin and simple, in other cases a radially striated ectoplasmic layer is present (figs. 104, 108), which has been variously described. From the inner integument, which may be homogeneous or fibrous, thick or thin, membranes or trabeculæ pass into the interior of the body, forming anastomosing partitions, and so producing a system of chambers of various sizes that do not communicate with one another (figs. 104, 108). These chambers are occupied by sickle- or bean-shaped bodies (spores or sporozoites), or various developmental stages of them. The oldest spores are found in the centre of the Miescher’s tubes or trophozoites. If they are not liberated they die there, so that the central chambers of the tube are empty and hollow.

In the youngest Sarcosporidia (40 µ in length) from the muscles of the sheep there occur, according to Bertram, small roundish or oval cells (4 µ to 5 µ), the nuclei of which are half their size, and are embedded in a granular protoplasmic mass. In somewhat larger, and therefore older, cylinders, the investing membrane of which already shows both layers, the cells have become larger (to 7 µ) and are more sharply outlined from each other (fig. 106). These uninucleate cells may be considered as pansporoblasts. In each pansporoblast division of the nucleus occurs (fig. 107), and meanwhile the pansporoblasts become isolated within the chambers, the dividing partitions of which originate from the granular protoplasm which is present between the pansporoblasts. The numerous uninucleate daughter forms produced within the chambers become spores direct (fig. 108).

The process commences in the centre of the cylinders or sarcocysts, and then progresses towards the extremities, the parasites meanwhile increasing in size, and new pansporoblasts being continually formed at the extremities (fig. 107).

The spores (sometimes called Rainey’s corpuscles), vary in shape according to the species, but are also of different form individually. They are mostly kidney-, bean- or sickle-shaped (fig. 109), and of small size, sometimes reaching 14 µ by 3 µ to 5 µ. They are apparently surrounded by a thin membrane, and at one extremity (according to the discovery of L. Pfeiffer, confirmed by van Eecke, Laveran and Mesnil) contain an obliquely striated body (fig. 109) often homologized with the polar capsule, while the greater part of the spore is taken up by the nucleate sporozoite. Several authors state that they have also observed filamentous appendages (polar filaments) at one end of the spores, and have seen two kinds of spores in the same Sarcosporidium. Spores of various species of Sarcosporidia may contain metachromatic granules, often centrally placed (fig. 109). These granules may be metabolic or possibly may contain toxin (see below).

The gymnospores of Sarcocystis muris, from the mouse, show active boring movements when kept in saline solution warmed to 35° or 37° C. S. muris is very deadly to its host. From their structure the spores do not appear to have great powers of resistance to external conditions. They measure 12 µ by 3 µ to 4 µ or less.

Laveran and Mesnil (1899) isolated a toxin from S. tenella of the sheep and called it sarcocystin. This substance is especially pathogenic to experimental rabbits.

The duration of life of the Sarcosporidia is a comparatively long one. The affected muscular fibres may remain intact and capable of performing their functions for a long time, but at last they perish, if the host lives long enough. Thus the Sarcosporidia of the muscles are then enveloped only by sarcolemma, and finally, when this likewise disappears, they fall into the intra-muscular connective tissue. In many cases the Sarcosporidia die off within their hosts, this, according to Bertram, being brought about by a disintegration of the spores in the central chambers. In other cases the leucocytes play a part in the destruction of the Sarcosporidia, and sometimes it happens that lime salts are deposited in and around the vacant cylinders.

In some places pigs, sheep, mice and rats are infected with sarcosporidiosis to a remarkable extent, in certain cases almost reaching 100 per cent. Young animals also are infected, and perhaps infection only takes place during youth.

Although the natural mode of transmission of the Sarcosporidia remains to be determined, yet various experimental researches on the problem are of interest and importance. Theobald Smith (1901) found that mice could be experimentally infected with S. muris by feeding them with the flesh of other infected mice. The incubation period was a long one, namely forty to fifty days. Thus, on the forty-fifth day after feeding young Sarcosporidia were found, and seventy days after feeding spore formation began. Ripe spores were found two and a half to three months after the commencement of these experiments. This mode of infection--a cannibalistic one--hardly seems likely to be the natural method for the infection of sheep and ruminants generally. Smith’s researches have been confirmed. Nègre[225] (1910) found that the fæces of mice fed on infected muscular tissue were infective to other mice when ingested by them. Negri[226] infected guinea-pigs with S. muris by feeding them on infected mouse flesh, and found that the parasite in guinea-pigs showed different characters from those exhibited by it in mice. Darling[227] also succeeded in infecting guinea-pigs with S. muris, and Erdmann infected mice with S. tenella (from the sheep).

[225] C. R. Soc. Biol., lxviii, p. 997.

[226] Centralbl. f. Bakt., Orig., xlvii, p. 612; see also xlvii, p. 56; lv, p. 373.

[227] Journ. Exptl. Med., xii, p. 19.

According to Erdmann[228] (1910) the Sarcosporidian spore germinates in the intestine of the host, which has recently ingested infected material. The spore liberates its contained toxin--sarcocystin--which acts upon the adjacent intestinal epithelium, whereby the latter is shed, and an amœbula creeps out of the spore. The amœbula is able to penetrate the denuded area and get directly into the lymph-spaces of the submucous coat of the intestine. The first period of development, lasting some twenty-eight to thirty days, is said to be passed in the lymph-spaces of the intestine. Later the amœbula reaches a muscle fibre. Writing in May, 1914, Erdmann[229] records the appearance of small amœboid and schizogony forms six days after infection of the host. Crawley[230] (1913) controverts some of these statements and considers that the Sarcosporidian spore, still sickle-shaped, bores its way into the epithelial cells of the intestine and comes to rest there. The spore then becomes round or elliptical, and peripheral masses of chromatin appear within it, suggesting schizogony. This happens about twelve hours after feeding, and in twenty-four hours the spores appear to have left the intestine. More recently (May, 1914), Crawley[231] considers that there is sexual differentiation among the Sarcosporidian spores, a few hours after their ingestion by the host.

[228] Sitz. Gesell. naturf. Freunde zu Berlin, p. 377.

[229] Proc. Soc. Exper. Biol. and Med., xi, p. 152.

[230] Science, xxxvii, p. 498.

[231] Proc. Acad. Nat. Sci., Philadelphia, May, 1914, p. 432.

Interesting discussions have occurred as to the site of the toxic sarcocystin within the spore. Metachromatic granules occur in the middle of the Sarcosporidian spore (fig. 109), and the toxin may be contained in these grains, as they disappear, according to Erdmann, before the amœbula penetrates the denuded intestinal wall. However, a polar capsule, containing a polar filament, may be present at one end of a Sarcosporidian spore. Laveran and Mesnil described a striated area at the more pointed end of the spore of S. tenella, which area they consider to represent a polar capsule. Fantham[232] (1913) found a vacuole-like, polar capsule area in the spores of S. colii from the African mouse-bird. The sarcocystin may be contained in the polar capsule. The nucleus of the spore is generally at the opposite, blunter end.

[232] Proc. Cambr. Philosoph. Soc., xvii, p. 221.

Again, various authors have stated that Sarcosporidian spores may occur in the blood of the host at times. If so, then an intermediate host may be concerned in their transmission. Perrin suggested that Sarcosporidia might be spread by blow-flies and flesh-flies.

The classification of the Sarcosporidia as proposed by R. Blanchard, which was based on their various habitats, can no longer hold, because the same species may occur in the muscles as well as in the connective tissue. For the present, the few species that are known may be placed in one genus, Sarcocystis, Ray Lankester, 1882.

The following species of Sarcocystis are of interest:--

S. miescheriana, Kühn, 1865, in the pig.

S. bertrami, Doflein, 1901, in the horse.

S. tenella, Railliet, 1886, in sheep. S. tenella bubali in buffaloes in Ceylon and Egypt.

S. blanchardi, Doflein, 1901, in cattle.

S. muris, Blanchard, 1885, in the mouse, to which it is lethal.

S. hueti, Blanchard, 1885, in the seal.

S. colii, Fantham, 1913, in the African mouse-bird, Colius erythromelon.

Also various Sarcosporidia from antelopes, monkeys, opossum, birds, the gecko and wall-lizard are known.

The spores of S. muris, S. bertrami, S. tenella, and S. colii can multiply by longitudinal fission.

SARCOSPORIDIA OBSERVED IN MAN.

(1) Lindemann[233] found on the valves and in the myocardium of a person who had died of dropsy certain brownish masses, 3 mm. in length and 1·5 mm. in breadth which he regarded as gregarines. If these were actually independent animal organisms it may be suggested that they were Sarcosporidia. Rivolta (1878) named the species S. lindemanni.

[233] “Ueb. d. hyg. Bdtg. d. Gregarinen,” Dtsche. Ztschr. f. Staatsarzneikunde, 1868, xxvi, p. 326.

(2) Rosenberg[234] found a cyst 5 mm. in length and 2 mm. in breadth in a papillary muscle of the mitral valve of a woman, aged 40, who had died from pleuritis and endocarditis. The cyst contained no scolex nor hooklets of tænia. Numerous small refracting bodies, round, oval or kidney-shaped, were found in a daughter cyst, as well as sickle-shaped bodies. The description hardly appears to indicate Sarcosporidia.

[234] “Ein Befund von Psorosp. in Herzmusk d. Menschen,” Ztschr. f. Hygiene, 1892, xi, p. 435.

(3) Kartulis[235] observed Miescher’s cylinders of various sizes in the liver (?) and in the muscular system, of a Sudanese who had succumbed to multiple abscesses of the liver and abdominal muscles. This may be considered as the first actual case of the occurrence of Sarcosporidia in man. Koch in 1887 described a case in Egypt.

[235] Kartulis, “Ueb. pathog. Protoz. b. Menschen,” Ztschr. f. Hyg. u. Inf., 1893, xiii, p. 1. Compare also Braun, M., Die Thier. Par. d. Mensch., 2nd Edit., Wrzbg., 1895, p. 92; Braun, M., “Z. Vork. d. Sarcosp., b. Menschen,” Centralbl. f. Bakt. 1895, xviii, p. 13.

(4) The case reported by Baraban and St. Remy[236] was at once demonstrated as certain. It related to a man who had been executed, and in the laryngeal muscles of whom Sarcosporidia were found; the length of the parasites varied between 150 µ and 1,600 µ, their breadth between 77 µ and 168 µ. The affected muscular fibres were distended to four times their normal thickness. This species was described by Blanchard as “Miescheria” muris, but according to Vuillemin, it was more probably Sarcocystis tenella of the sheep.

[236] “Sur un cas de Tub. Psorosp. ob. chez l’homme,” C. R. Soc. Biol., Paris, 1894 (x), I, p. 201. “Le Parasitisme d. Sarcosp. chez l’homme,” Bibliogr. Anat. 1894, p. 79.

(5) Vuillemin has also described a case of Sarcosporidia found in the muscles of a man who died from tubercle at Nancy. The author considered that the parasite corresponded to S. tenella.

(6) Darling[237] (1909) found Sarcosporidia in the biceps of a negro from Barbados.

[237] Arch. Internal Med., III, p. 183.

The Myxosporidia, Microsporidia, Actinomyxidia and possibly the Sarcosporidia may be included within the section *Cnidosporidia* (Doflein), since they possess spores containing polar capsules.

Order. *Haplosporidia*, Caullery and Mesnil.

The Haplosporidia are a group of organisms having both a simple structure and life-history. The simplicity may represent a primitive condition or may be due to degradation resultant on parasitism, and thus it is possible that the group is not a homogeneous one. The order Haplosporidia was created by Caullery and Mesnil in 1899, and includes parasites of rotifers, annelids (fig. 110), crustacea, fish, prochordates and man. They may be present in the body cavity or alimentary tract, and can also occur in the septum nasi of man, in the nervous system of Cephalodiscus, and in tumours of fish.

As the name implies, the spores of the Haplosporidia are simple, without polar capsules, and are uninucleate. In some genera, e.g., Haplosporidium, Urosporidium (fig. 111) there is a spore-coat or sporocyst which may be elongate or spiny. The developmental cycle of a Haplosporidian, such as Haplosporidium or Bertramia, begins with a small, uninucleate cell, often rounded, possessing a cell membrane that may be prolonged into processes. Growth takes place, coupled with an increase in the number of nuclei, so that a multinucleate trophozoite is produced. Later, this multinucleate trophozoite becomes segmented into a number of ovoid or spherical pansporoblasts, which give rise to few (one to four) spores. Such a spore, when set free, begins the life cycle over again.

More recently (1905–1907) two important organisms have been described and included in this group, namely, Neurosporidium cephalodisci[238] (Ridewood and Fantham) from the nervous system of the prochordate, Cephalodiscus nigrescens, and Rhinosporidium kinealyi (or seeberi) from the septum nasi of man. In the case of Rhinosporidium and Neurosporidium, after the uninucleate spore has grown into a multinucleate trophozoite, the latter segments into uninucleate pansporoblasts, as in the preceding cases. A difference then occurs, for each pansporoblast enlarges, its nucleus divides and a “spore-morula” is formed. Thus a multinucleate pansporoblast or spore-morula, divided into many uninucleate sporoblasts (spore mother cells) is produced, and each sporoblast without further change becomes a uninucleate spore.

[238] Quart. Journ. Microsc. Sci., li, p. 81.

The Haplosporidia have therefore been divided by Ridewood and Fantham (1907)[239] into two sections:--

[239] See Fantham, Brit. Assoc. Reports, 1907, p. 553.

(1) The Polysporulea, wherein the pansporoblast gives rise to a number of spores (nine or more), e.g., Rhinosporidium, Neurosporidium.

(2) The Oligosporulea, wherein the pansporoblasts give rise each to a few (four) spores or to only a single spore, e.g., Haplosporidium, Bertramia, Cœlosporidium, Ichthyosporidium.

*Rhinosporidium kinealyi*, Minchin and Fantham, 1905.

Rhinosporidium kinealyi, parasitic in man, must now be considered in greater detail. This organism was found in nasal polypus in India, and has since been recorded from the ear as small nodules in the external auditory meatus. The Indian cases came from the neighbourhoods of Calcutta and Madras, and the parasite has been seen in Ceylon. Similar structures have since been described from the United States and South America.

The Rhinosporidium polypus is said not to be particularly painful, though nasal forms must interfere with breathing to some extent. The first nasal polyp reported from India formed a vascular pedunculated growth on the septum nasi and was about the size of a large pea or raspberry. It was compared with a raspberry, being red in colour with a number of small whitish dots upon its surface. When the tumour was cut, a number of similar whitish dots were seen within. These were the cysts of Rhinosporidium. According to Minchin and Fantham[240] (1905), they vary considerably in size and measure up to 200 µ or 250 µ in diameter. Each possesses a cyst wall which varies in thickness in different cysts. Its outer wall is always firm and distinct, the inner limit being less definite at times. Each large cyst is filled with numbers of spherical or oval bodies, showing every gradation between small ones at the periphery and large ones at the centre (fig. 112). Roughly, three zones of parasites can be distinguished in a large cyst, a peripheral set consisting of the youngest parasites, an intermediate group and a central, oldest zone. A large cyst may possess a pore for the egress of its contents. Some of the cysts show polar distribution of the zones.

[240] Quart. Journ. Microsc. Sci., xlix, p. 521.

The youngest forms of Rhinosporidium are difficult to detect. They are small, granular masses, round, ovoid or irregular and at times even amœboid in appearance. These are young trophozoites. They increase in size, but encystment occurs early, the outer layer becoming firm so that the organisms have a definite contour. Each is soon multinucleate and the cytoplasm segments around the nuclei. The cyst thus becomes full of uninucleate pansporoblasts or sporonts, with a peripheral layer of undifferentiated protoplasm. The pansporoblasts grow in size. In the larger cysts the formation of pansporoblasts progresses at the expense of the peripheral layer of protoplasm, which, however, continues to grow, so that the cyst as a whole increases in size. The pansporoblasts at first are uninucleate (fig. 112, a), and then undergo nuclear multiplication. This is well seen in the intermediate zone of parasites, where the pansporoblasts show first one, then two, then four or more spores (fig. 112, b), while in the oldest centrally placed pansporoblasts, about a dozen or sixteen closely packed spores (fig. 112, c), can be seen. The spore is small and rounded, and its nucleus is clear and distinct. The fully formed pansporoblast or spore morula becomes surrounded by a membrane.

Certain of the cysts have been found in a ruptured condition, whereby the spores have been liberated into the surrounding tissue. It is almost certain that the spores serve for the auto-infection of the host, for though the tumours of Rhinosporidium seemed to have been removed entirely, it has been found that they recur, some minute fragment of the parasite having probably been left behind. The method whereby the parasite reaches new hosts has not yet been determined, and it would be of interest if its life-history could be more fully investigated.

The Asiatic specimens of R. kinealyi were first described in detail by Minchin and Fantham (1905) from material briefly reported to the Laryngological Society of London in 1903, by O’Kinealy. Material obtained by Dr. Nair, of Madras, was described by Beattie[241] in 1906. This material came from Cochin. Castellani and Chalmers have found similar polypi in Ceylon.

[241] Journ. Pathol. and Bacteriol., xi, p. 270; and Brit. Med. Journ., Nov. 16, 1907, p. 1402.

Wright[242] has described the parasite from Memphis, Tennessee. Seeber[243] in 1896 described nasal polypi in Buenos Ayres, and in 1900 Wernicke named the parasite therein Coccidium seeberi. Seeber’s parasite is a Rhinosporidium, R. seeberi, and may ultimately be found to be the same as R. kinealyi. Ingram[244] reports Rhinosporidium cysts, with pores in the cyst walls, in conjunctival polypus and in papilloma of the penis in India. Zschokke has reported the presence of Rhinosporidium in horses in South Africa.

[242] New York Med. Journ., December 21, 1907, p. 1149.

[243] La Ciencia Medica (Buenos Ayres), 1912.

[244] Lancet, September 3, 1910, p. 726.

Class IV. *INFUSORIA*, Ledermüller, 1763.

The Infusoria (or Heterokaryota, Hickson, or Ciliophora, Doflein) include the Ciliata and the Suctoria. A few authorities, including Braun, raise the Suctoria (or Acinetaria) to separate rank as a class, but this is not widely followed.

The body of the Ciliata usually is bilaterally symmetrical and is enveloped in a cuticle which has numerous openings for the protrusion of the cilia. Most kinds have a fixed shape, whilst changes in the form of others are brought about by the contractions of the body substance. The latter exhibits hyaline ectoplasm, in which myonemes, and occasionally also trichocysts (minute spindle-shaped bodies) appear, and granular endoplasm which may contain numerous vacuoles. The cilia, on whose various arrangements the classification is based, are always processes of the ectoplasm. Their form varies; they may be hair-like, or more rarely thorn-like, spur-like, or hook-shaped; undulatory membranes also may occur, which are probably composed of fused cilia.

With the exception of some of the parasitic species, an oral cavity, peristome or cytostome, is always present. It is frequently beset with cilia or provided with undulatory membranes, which help to waft the food inwards; sometimes there is an anal aperture (cytopyge) generally placed at the opposite pole of the organism. A cytopharynx fringed with cilia or sometimes with a specialized supporting apparatus is connected with the peristome. Vacuoles form round the ingested food, and in many species a constant rotation goes on in the endoplasm. Often one, and sometimes two contractile vacuoles are present, the frequency of the pulsations of which depends on the surrounding temperature. Sometimes special conducting channels lead to the vacuoles, or there are outlet channels leading to the exterior.

There is in almost every case a large nucleus (macronucleus), and lying close up to it a small nucleus (micronucleus). The form of the large nucleus varies according to the species. Numerous nuclei are not very common, but these occur in Opalina, which lives in the hind-gut of amphibia, and is also distinguished by the absence of an oral aperture.

Reproduction is effected by binary fission; less commonly, after encystment, by multiple division, or by budding. The divisions can be repeated many times, but finally cease, and then the conjugation of two specimens brings about a regeneration, particularly of the nuclei. Numerous examinations (Bütschli, Hertwig, Maupas, Calkins) have demonstrated that after two individuals have associated by homologous parts of the body, the micronucleus separates from the macronucleus, becomes larger and divides twice by mitosis, so that four micronuclei are present in each one of the two individuals forming the couple. Three of these nuclei perish and become absorbed, the fourth gradually passes to the portion of protoplasm connecting the two conjugants, which has originated by absorption of the cuticle at the point of contact of the conjugants. After a further division one micronucleus of each conjugant passes over into the other conjugant, and fusion ensues between the two micronuclei of each individual. Complicated changes and divisions may occur, but only the main principles can be noted here. A new nuclear body is thus formed in each conjugant, and soon divides into two. Of the segments thus produced one becomes a micronucleus, and one or several of the others, as the case may be, form or amalgamate into a new macronucleus, the old macronucleus usually perishing or becoming absorbed during the conjugation. Usually, sooner or later, the two conjugants separate, or may have separated already, and again multiply independently by fission until a series of divisions by simple fission is again followed by conjugation. The theoretical significance of conjugation cannot be dealt with fully here. It may be remarked, however, that the macronucleus plays no part in it, but governs entirely the metabolism of the Infusorian, whereas the micronucleus is essentially a generative nucleus from which macro- and micro-nuclei are again and again produced.

Encystment amongst the Infusoria is very general, and is essentially a means of protection when the surrounding medium dries up. Doubtless these cysts are frequently carried long distances by the wind, which explains the wide geographical distribution of most species. Also, multiplication often takes place in the encysted condition.

Some Infusoria live a free life, others are sedentary; the latter form colonies in fresh as well as in salt water. Numerous species are parasites of various lower and higher animals,[245] and a few also are parasitic in man.

[245] It may be stated that numerous peculiarly shaped species live in the stomach of ruminants, others in the colon of horses. Several species are found in the rectum of frogs and toads; others, again, on the surface of the bodies of fishes; and various other species exist in and on the bodies of invertebrate animals.

The Prague zoologist, v. Stein, introduced a classification of the Infusoria that has been almost universally adopted. It is founded on the different position of the cilia on the body. Though, no doubt, artificial, it is a convenient system. Bütschli has compiled a better one.[246] But for our purpose Stein’s system is sufficient:--

[246] Bronn’s Cl. u. Ordn. d. Thierr., i, Protozoa, Part 3, Infusoria.

Order 1. Holotricha, Infusoria with cilia that are evenly distributed over the entire body.

Order 2. Heterotricha, ciliated all over like the Holotricha, but having stouter cilia about the peristome.

Order 3. Hypotricha, only ciliated on the ventral surface.

Order 4. Peritricha, with only a ring of spiral cilia, mostly sedentary.

The Infusoria observed in man belong to the order Heterotricha, with few exceptions.

Genus. *Balantidium*, Claparède et Lachmann.

Heterotrichous Infusoria of oval or bag-like form and almost circular on transverse section; the anterior extremity narrowed, the posterior end broad and rounded off, or also narrowed; the peristome starting at the anterior end is broadest there and becomes narrower as it gradually obliquely approaches towards the posterior extremity. There are coarse cilia along the entire left border and the anterior part of the right border. Longitudinal striation is distinct and regular. There are two contractile vacuoles on the right, and occasionally also two or more to the left. The anus (cytopyge) is terminal. The macronucleus is usually horse-shoe or kidney-shaped, sometimes oval; the micronucleus contiguous. Reproduction is by binary fission and conjugation, and encystment occurs. The cysts are spherical or oval. These ciliates are parasitic in the large intestine of human beings and pigs, in Amphibia, and in the body cavity of polychæte Annelida.

*Balantidium coli*, Malmsten, 1857.

Syn.: Paramæcium coli, Malmsten, 1857.

The body is oval, 60 µ to 100 µ in length (up to 200 µ according to Janowski), and 50 µ to 70 µ in breadth. The peristome is funnel-shaped or contracted, the anterior end being then broadened or pointed according to the degree of contraction (figs. 113, 114). The ecto- and endo-plasm are distinct, the latter is granular, containing drops of fat and mucus, granules of starch, bacteria, and occasionally also red and white blood corpuscles. There are usually two contractile vacuoles, seldom more. The anus (cytopyge) opens at the posterior extremity. The macronucleus is bean- or kidney-shaped, rarely oval; the micronucleus is spherical.

Balantidium coli lives in the large intestine of man, in the rectum of the domestic pig, and has been found in monkeys. It propagates by transverse division, but conjugation and encystment are known to take place.[247] Transmission to other hosts is effected by the cysts of the parasite (fig. 114).

[247] According to Gourvitch (“Bal. coli. Darmk. d. Menschen,” Russ. Arch. f. Path., klin. med. u. Bact., Petrograd, 1896), the conjugated Balantidia are supposed to fuse with each other and form oval cysts two or three times the size of the free organisms, and to divide into numerous globules within the cystic membrane; the process, however, has hitherto not been confirmed. The supposed Balantidium cysts appeared in two patients who were simultaneously suffering from Dibothriocephalus latus, after the administration of anthelminthics. It therefore seems, according to the description, that in reality these forms were actually abnormally large, possibly swollen, young eggs of the tape-worm mentioned.

Balantidium coli, first seen by Leeuwenhoek, was described by Malmsten in 1857 in a man aged 35 years, who had two years previously suffered from cholera, and since then had been subject to diarrhœa. The examination showed an ulcer in the rectum above the mid sphincter ani, in the sanguineous purulent secretion of which numerous Balantidia were swimming about. Although the ulcer was made to heal, the diarrhœa did not cease and the stools contained numerous Balantidia, the number of which could only be decreased by extensive enemas of hydrochloric acid.

The second case related to a woman who was suffering from severe colitis, and who died ten days after admission. The malodorous, watery evacuations contained innumerable Balantidia, in addition to pus, and at the autopsy the anterior portion of the large intestine was found to be infested with them.

Subsequently this parasite has often been observed in human beings, and various cases have been recorded. These occurred in Russia, Scandinavia, Finland, Cochin China, Italy, Germany, Serbia, Sunda Islands, Philippine Islands, China, and in other parts of Asia and in America. Other cases were reported by Askanazy, Ehrnroth, Klimenko, Nagel, Koslowsky, Kossler, Waljeff, Strong and Musgrave, Glaessner[248] and others. Sievers found B. coli very common in Finland.

[248] Centralbl. f. Bakt., Orig., xlvii, p. 351.

In the majority of the cases described by Sievers from Finland, and in other cases from Central Europe, the patients suffered from obstinate intestinal catarrh, which did not always cease even after the Balantidia had disappeared. On the other hand, Balantidia have occasionally still been found to persist, though in small numbers, after the catarrh has been cured. Some authors, nevertheless, do not regard Balantidia as the primary cause of the various diseases of the large intestine, which often commence with the development of ulcers, but they consider that they may aggravate these diseases and render them obstinate. According to Solowjew, Askanazy, Klimenko and Strong and Musgrave, however, the parasites penetrate the intestinal wall, and give rise to ulcerations which may extend deeply into the submucosa, and even be found in the blood and lymphatic vessels of the intestinal wall. According to Stokvis, B. coli occurs also in the lung; at all events this author states that he found one living and several dead paramæcia (?) in the sputum of a soldier, returned from the Sunda Islands, who was suffering from a pulmonary abscess. Sievers has shown that B. coli might occur in persons not suffering from intestinal complaints, but E. L. Walker[249] (1913) states that every person parasitised with B. coli is liable sooner or later to develop balantidian dysentery.

[249] Philip. Jl. Sc., Sec. B, viii, p. 333.

Since Leuckart confirmed the frequent presence of B. coli in the rectum of pigs, and corresponding observations were made in other countries, the pig is universally considered to be the means of the transmission of Balantidium to man. The encysted stages only serve for transmission, because, according to all observations, the free parasites have a very small power of resistance. They perish when the fæces have become cool; they cannot live in ordinary, slimy, or salt water. As they are killed by acids even when much diluted, they cannot pass through the normal stomach alive except under the most unusual circumstances. The pigs, in whose intestines the Balantidium appears to cause little or no disturbance, evacuate numerous encysted Balantidia with the fæces, and their occasional transference to man brings about their colonization there, but perhaps only when a disease of the colon already exists.

Experimental transmission of the free parasites to animals (per os or per anum) yielded negative results, even in the case of pigs. Casagrandi and Barbagallo (1896), however, had positive, as well as negative, results. They employed healthy young cats, or cats in which catarrhal entero-colitis had been artificially induced (which in other experiments is apt to cause the death of the animals experimented upon in about six or seven days), or finally cats that had dilatation of the rectum with alkaline reaction of the fæces. An attempt to infect three healthy cats by injecting human fæces containing Balantidium into the rectum proved negative, in so far as the fæces of the experimental animals had an acid reaction and contained no Balantidia, but at the autopsy performed eight days after infection a few encysted parasites were found in the mucus of the ileum. In the case of four cats suffering from entero-colitis, into which human fæces containing Balantidia were introduced per os, Balantidium cysts were found in the fæces three days after the last ingestion. Great numbers, moreover, were found in the cæcum and the posterior part of the small intestine at the autopsy of the animals, which died about eight days after the commencement of the experiments. Actual colonization, therefore, was not effected in either series of experiments. Free or encysted Balantidia of pigs were used for further experiments. The experiments proved negative when fæces containing cysts were injected into the rectum of healthy cats (three experiments), or cats (two) suffering from spontaneous intestinal catarrh, or when such material was introduced per os into three healthy cats. In the case of two cats with intestinal catarrh artificially produced, a small number of the active Balantidia injected into the rectum remained alive. Larger quantities of fæces containing encysted Balantidia were introduced into two other cats affected with the same complaint. These, certainly, did not appear in the fæces, but small numbers, free and alive, were found in the cæcum. Similarly, encysted Balantidia were introduced into two cats with dilated rectum, and whose fæces had an alkaline reaction. In these cases no parasites appeared in the fæces, but three and five days later, when the two animals were examined, a very small number were discovered free in the large intestine. Klimenko did not succeed in infection experiments with B. coli on young dogs, whose intestines had been artificially affected by disease.

More recent experiments by Brumpt have shown that young sucking pigs can be infected with Balantidium from infected monkeys (Macacus cynomolgus) and suffer heavily from the same, whereas the Balantidium of the pig is rarely harmful to its host. This and previous experiments may be thought to suggest that there are perhaps several pathogenic species, and also that harmless strains of Balantidium may occur. At the same time, it must be remembered that a large proportion of the cases recorded of Balantidian colitis occur among swineherds and butchers, that is, among people in frequent contact with pigs. Morphologically, there are practically no differences between the Balantidia found in man, monkeys and pigs, and it is probable that one species only, under slightly different environmental conditions, may be responsible for the colitis observed. In any case, efficient prophylactic measures should be taken against balantidiasis in countries where it may occur, by confining the pigs and not allowing them to run in yards and dwellings.

E. L. Walker (1913) has given a good summary of work on balantidiasis. His own researches in the Philippines showed that monkeys could be infected by Balantidia both from pigs and men. Parasites may appear in the stools only at infrequent intervals. He believes that the ciliates are the primary etiologic factor in the symptoms and lesions of balantidian dysentery.

Behrenroth (1913) has given an interesting account of Balantidium coli and its pathogenic significance.

*Balantidium minutum*, Schaudinn, 1899.

The body is of oval form, with the anterior extremity pointed, and posterior extremity broad and rounded (fig. 115). The length is 20 µ to 32 µ, and the breadth is 14 µ to 20 µ. The peristome, which is fissure-like, extends to the centre of the body (fig. 115). The right lateral border of the peristome is beset with cilia the same length as those of the body, the left side terminates in a thin hyaline membrane that extends towards the back, and can pass over to the right side. A row of longer and stronger cilia (cirri) are on the left border of the peristome. The cuticle is refractile, the ectoplasm hyaline and the endoplasm granular, with numerous food vacuoles.

A single contractile vacuole lies dorsally and to one side at the posterior extremity. The macronucleus, which is always spherical, is central and is 6 µ to 7 µ in diameter. The micronucleus, close in front of it, only measures 1 µ (fig. 115). The cysts are oval.

These parasites were found in numbers in the evacuations of a man aged 30, who was born in Germany and had repeatedly travelled between Hamburg and North America, where he made long stays. The patient came to the Charité in Berlin to seek advice for constipation alternating with diarrhœa accompanied by abdominal pain.

A second case (the parasite of which was described as Colpoda cucullus by Schulz) was observed in a patient in the same institution.

As, in both cases, the parasites only appeared during the diarrhœa, and disappeared as soon as the fæces had assumed a normal consistency, or could only be demonstrated in a few encysted specimens, it may be assumed that the small intestine or the duodenum is their habitat.

Genus. *Nyctotherus*, Leidy, 1849.

Flat, heterotrichous Infusoria, kidney- or bean-shaped. The peristome commences at the anterior pole of the body and extends along the concave side to the middle, where the oral aperture is situated. The cytopharynx is oblique and is more or less curved. The cytopyge is at the posterior extremity, where a single contractile vacuole is also situated. The macronucleus is almost in the centre of the parasite. The members of this genus live parasitically in the intestine of amphibia, insects and myriapods, and at least one species is found in man.

*Nyctotherus faba*, Schaudinn, 1899.

The body is bean-shaped, and a little flattened dorso-ventrally. It is 26 µ to 28 µ long, 16 µ to 18 µ broad, and 10 µ to 12 µ thick (fig. 116). The peristome is on the right border and extends to the middle; at the left there are large adoral cilia, the cilia on the right border not being larger than those on the body. The cytopharynx is short, slightly curved and turned backwards. The contractile vacuole is large, spherical, situated at the posterior extremity, and its contents are voided through the anus at its left. The macronucleus is in the centre of the body; it is globular (6 µ to 7 µ in size), and contains four or five chromatin masses. The micronucleus lies close to it, and is spherical or somewhat elongate measuring 1 µ to 1·5 µ (fig. 116). The cysts are oval.

This species has hitherto only been seen once in the same patient in whom Balantidium minutum was discovered.

*Nyctotherus giganteus*, P. Krause, 1906.

Under the name Balantidium giganteum n. sp., P. Krause described an Infusorian which was repeatedly observed with Trichomonas intestinalis in the alkaline evacuations of a typhoid patient in Breslau. The body is ovoid, narrower and rounded anteriorly and broader and stunted posteriorly. The peristome lies to one side; the macronucleus is bean-shaped, the micronucleus small and globular; one or two vacuoles are present. The anus is at the farther end. The organism is 90 µ to 400 µ long, 60 µ to 150 µ broad (fig. 117). After a prolonged stay outside the body, it becomes rounded and encystment occurs. In the thermostat the Infusoria remain alive at 37° C. for five weeks.

The species, however, hardly belongs to Balantidium, but to all appearances is a Nyctotherus and is distinguished from N. faba by the difference in size.

[*Nyctotherus*] *africanus*, Castellani, 1905.

In the fæces of a native of Uganda who suffered from sleeping sickness and diarrhœa and had in his intestine Ascaris lumbricoides, Trichocephalus trichiurus and Ancylostoma duodenale, Castellani found a curiously shaped Infusorian, 40 µ to 50 µ long, and 35 µ to 40 µ broad, with spherical macro- and micronucleus and a contractile vacuole (fig. 118). He included the organism in the genus Nyctotherus, perhaps wrongly, or the parasite may have been deformed. After the patient’s death the same parasite was found in the intestine and especially in the cæcum.

G. Lindner, in Cassel, studied certain peritrichal Infusoria (stalkless Vorticella), and connected them, probably incorrectly, with the most varied diseases of man and domestic animals, even with Sarcosporidia of pigs. It may be mentioned that according to a communication by letter from Schaudinn, Vorticella may be found in freshly evacuated fæces, but always only after the administration of a water enema. In spite of this, several other investigators mention Vorticellæ as intestinal parasites of man.

The Chilodon dentatus (Ehrenberg) recorded in 1903 by J. Guiart as a parasite of man, which may be found in all infusions, can hardly have lived in the man from whose fæces it was cultivated, but may represent a chance admixture both in the fæces and the cultivations. C. uncinatus was also found as a chance parasite of man by Manson and Sambon. According to Doflein[250] (1911) certain Chilodon-like organisms have been found by Selenew in prostate secretions in gonorrhœa. Other species of the genus Chilodon are known, but only as ectoparasites (e.g., Chilodon cyprini, Moroff, 1902, from the skin and gills of diseased carp).

[250] Lehrbuch der Protozoenkunde, 3rd ed., p. 963.

A number of other parasitic Ciliates are known, among which Ichthyophthirius multifiliis, destructive to fish, is important. It lives in the skin and the layers immediately below it, forming small whitish pustules which may become confluent. The pustules are most common on the head and fins, but occur also on the eyes and gills of the host. The young parasite, which is one of many formed in a cyst, is very small. At first it is free swimming, but soon attaches itself to the skin of a fish. It bores inwards and becomes surrounded by the irritated skin. There it attains a relatively large size, being 500 µ to 750 µ and occasionally more in diameter. The body has a rounded terminal mouth, short cytopharynx and a number of minute contractile vacuoles. The macronucleus is large and horseshoe-shaped; the small micronucleus is only seen in the very young animal. When full grown, the organism encysts and forces its way to the surface and bursts through, leaving a small, gaping wound behind. The cyst sinks to the bottom of the water, nuclear multiplication occurs and a number of young parasites are produced, which leave the cyst and either attack new hosts or else perish.

Opalina ranarum, parasitic in the rectum and urinary bladder of frogs and toads, shows great degradation and simplification due to parasitism, possessing no separate micronuclei, no cytostome, cytopharynx or cytopyge. It has many macronuclei, and is a large parasite. During summer and autumn nuclear multiplication followed by division of the body occurs, the process being repeated after the daughter forms have grown to the size of their parent. In spring, the Opalina divide rapidly, but do not grow much before dividing again. Finally, tiny forms, containing three to six nuclei, encyst and pass from the host with the fæces. As these latter are greedily devoured by tadpoles, the Opalina gain new hosts in which they develop.

THE CHLAMYDOZOA.

The name Chlamydozoa was proposed by Prowazek in 1907 for a number of minute, problematic organisms (fig. 119) believed to be the causal agents of certain diseases in man and animals, such as vaccinia and variola, trachoma, inclusion blenorrhœa in infants, molluscum contagiosum, and bird epithelioma contagiosum. Other diseases possibly due to Chlamydozoa[251] are hydrophobia, measles, scarlet fever, foot-and-mouth disease, the “Gelbsucht” disease of silkworms, and perhaps even typhus (Prowazek, 1913). The subject is difficult and controversial and can only be briefly discussed here. It is known that the viruses in all these diseases can pass through ordinary bacterial filters, that is, they belong to the group of “filterable viruses.” At such periods the organisms are extracellular or free. It is also known that in many of these cases the virus produces definite and characteristic reaction-products or cell-inclusions in the infected cells, during the intracellular phase of the life-history of the organism. As the organisms to be considered are problematic, it will be convenient to summarize their history:--

[251] For a detailed account of the Chlamydozoa see Prowazek’s Handbuch der Pathogenen Protozoen, Bd. i (1911–12). Leipzig, J. A. Barth.

(1) Cell-inclusions, usually named after their discoverers, have been found in certain diseases, thus: In vaccinia Guarnieri’s bodies, in scarlet fever Mallory’s bodies, in hydrophobia Negri’s bodies, in trachoma Prowazek’s bodies occur.

(2) At first these characteristic cell-inclusions were considered to be actual parasitic organisms causing the diseases in question. The bodies received zoological names and attempts were made to work out their supposed development cycles. The supposed parasites of vaccinia and variola were referred to a so-called genus Cytoryctes, those of hydrophobia to Neuroryctes, of scarlet fever to Cyclasterium, while those of molluscum contagiosum were referred to the Coccidia. Calkins in 1904 studied in detail the cell-inclusions of vaccinia and small-pox, calling them Cytoryctes variolæ, Guarnieri. Calkins considered that in the stratified cells of the epidermis they passed through two cycles, the one cytoplasmic, the other intranuclear. The first is the vaccinia cycle, the second the pathogenic (intranuclear) variola cycle. It is hardly necessary to follow all Calkins’ stages here.

Negri (1909) described a cycle for Neuroryctes hydrophobiæ. Calkins refers both Cytoryctes variolæ and Neuroryctes hydrophobiæ to the Rhizopoda.

Siegel (1905) described quite different organisms under the name Cytorhyctes. He listed several species: C. vacciniæ; of vaccinia and small-pox, C. scarlatinæ of scarlet fever, C. luis of syphilis (this is probably the granule stage of Treponema pallidum), and C. aphtharum of foot-and-mouth disease.

(3) The afore-mentioned views were criticized, and the bodies were not considered to be living organisms but merely reaction products or cell-inclusions due to the effects of the virus on the host cells. Thus Guarnieri’s bodies were stated to consist of extruded nucleolar or plastin material, having no developmental cycle. It was further asserted that infection could be produced by lymph in which Guarnieri’s bodies had been destroyed. Similar assertions have been made regarding the Negri bodies, and others. The Cytoryctes, Neuroryctes, etc., are considered, according to these views, to be degeneration products of the nucleus or to be of a mucoid nature.

(4) More recently a positive belief has gained ground that there are true parasitic organisms causing these diseases, and that the parasites are very minute, being termed Chlamydozoa by Prowazek and Strongyloplasmata by Lipschütz.

The Chlamydozoa are characterized by (a) their very minute size, smaller than any bacteria, so that they can pass through bacterial filters; (b) they pass through intracellular stages, in the cytoplasm or the nucleus of the host cell, producing therein the reaction products or inclusions in the cell already recorded as characteristic or diagnostic of the diseases produced; (c) they pass through definite developmental cycles. Such a cycle consists essentially of growth and division. The mode of division of the Chlamydozoa resembles that of the centriole of a cell, by the formation of a dumb-bell-shaped figure. Two dots are observed connected by a fine line or strand which becomes drawn out and finally snaps across the middle. Prowazek and Aragão (1909) working on smallpox in Rio de Janeiro found that the chlamydozoal granules passed through a Berkefeld filter and that the filtrate was virulent. But if an “ultra-filter” were used, i.e., one coated with agar, then the granules were retained and the filtrate was no longer virulent. The surface of the ultra-filter was found to contain many granules.

The Chlamydozoa are parasites of epiblastic tissues (e.g., epidermal cells, nerve cells, conjunctival cells).

The life-history of a Chlamydozoön (fig. 119), such as that of vaccinia, is, according to Prowazek, Hartmann and their school, as follows:--

1. The infection begins with elementary bodies or elementary corpuscles which live at first extracellularly. An elementary body is a minute speck of chromatin, apparently devoid of cytoplasm, which can pass through a bacterial filter. It can enter a host cell, but the entry is not a process of phagocytosis.

2. Inside the host cell the elementary body grows in size, and becomes an initial body (fig. 119, a).

3. A reaction on the part of the host cell results, for nucleolar, plastin substance is extruded from the cell-nucleus and surrounds the parasitic initial body. The latter is thus enveloped in a mantle (hence the name Chlamydozoa, from χλαμὑς, a mantle), and the characteristic cell-inclusion (Guarnieri’s body, Negri’s body, etc.) is produced. The nucleolar, mantle substance probably represents the “cytoplasm” of Cytoryctes, described by Calkins.

4. The body next breaks up into a number of smaller bodies known as initial corpuscles. These, in their turn, divide by simple division (in the manner already described) into numerous elementary bodies (fig. 119). Thus, the life-cycle is completed.

The Chlamydozoa are, then, the minute granules inside the body of the Cytoryctes variolæ or the Neuroryctes hydrophobiæ, so that the whole body of the Cytoryctes or Neuroryctes corresponds to the mantle and parasite of the Chlamydozoön. The Cytoryctes group is said to cause destruction of the host cell. The Cytoöikon group (e.g., trachoma bodies) causes proliferation of the host cell.

In September, 1913, Noguchi[252] described the cultivation of the parasite of rabies in an artificial medium, similar to that used by him for the cultivation of Spirochæta recurrentis. The cultures were stated to be infective to dogs, rabbits and guinea-pigs. Levaditi, in December, 1913, stated that he had succeeded in cultivating spinal ganglia of rabid monkeys in monkey plasma.

[252] Journ. Exptl. Med., xviii, p. 314.

Noguchi and Cohen (November, 1913)[253] have succeeded in cultivating the so-called trachoma bodies, or at any rate bodies very closely resembling them morphologically. The medium employed was Noguchi’s ascitic fluid and rabbit kidney medium, as used for spirochætes. The coarser cultural forms stained blue with Giemsa’s solution, the finer ones stained red. Attempts to infect monkeys from the culture tubes failed.

[253] Idem, p. 572.

From their behaviour on treatment with such reagents as saponin, bile and sodium taurocholate, Prowazek considers that the Chlamydozoa approach the Protozoa.

* * * * *

PROTOZOA INCERTÆ SEDIS.

*Sergentella hominis*, Brumpt, 1910.

Et. and Ed. Sergent in 1908 found vermiform bodies about 40 µ long by 1 µ to 1·5 µ broad in the blood of an Algerian suffering from nausea and cold sweats, without other symptoms. The bodies were pointed at each end, with a somewhat ill-defined nucleus in the middle. Their systematic position is doubtful.

----------------------------------------------------------------- |NOTE.--An Appendix on Protozoology will be found on pp. 733–752. | |This has been prepared in order to incorporate a number of new | |additions to knowledge made since the body of the book was | |printed off. | -----------------------------------------------------------------

B. *PLATYHELMINTHES*, or Flat Worms.

BY

J. W. W. STEPHENS, M.D., B.C., D.P.H.

DEFINITION: Bilaterally symmetrical animals without limbs, the form of which is leaf or tape-like, rarely cylindrical, and whose primary body cavity (segmentation cavity) is absent, the cavity being filled by a mesenchymatous tissue (parenchyma).

The mouth is either situated at the anterior end of the body, or is shifted more or less backwards on to the flat ventral surface. The alimentary canal consists of a short fore-gut, which is frequently provided with a muscular pharynx, and of a simple forked or branched mid-gut; there is neither a hind-gut nor an anus; in one class, the Cestodes, the alimentary canal has entirely disappeared except for muscular remnants in the scolex.

The INTEGUMENT OF THE BODY consists either of a ciliated epithelium of only one layer (Turbellaria), or of a cuticle and gland-like cells embedded in the parenchyma, or subcuticular layer (Cestodes, Trematodes). The dermo-muscular layer consists of annular, longitudinal, and even diagonal fibres, while the parenchyma is traversed by dorso-ventral fibres.

The central NERVOUS SYSTEM, which is embedded in the parenchyma of the body, consists of cerebral ganglia, united together in the shape of dumb-bells, and of two or more longitudinal MEDULLARY FASCICLES, often forming transverse anastomoses. Organs of sense usually occur only in the free-living species, more rarely during the free-living stages of a few parasitic species and in a few ectoparasitic forms.

[In Platyhelminthes simple eye-spots frequently occur, and in a few an auditory vesicle.]

BLOOD-VESSELS and definite RESPIRATORY ORGANS are lacking [except in Nemertinea]; the EXCRETORY APPARATUS (formerly termed water-vascular system) is typical of the entire class. It commences in the interstices of the parenchyma, with peculiar terminal cells (ciliated funnels), which will be described later (p. 219), the capillary processes of which go on uniting into larger branches, and finally form two large collecting vessels, which, sometimes separately and sometimes united, open to the exterior through one, two, or numerous pores.

Nearly all the Platyhelminthes are HERMAPHRODITIC, and in nearly all there are, in addition to the ovaries producing ova, other glands attached to the female genital apparatus, namely, the vitellaria or yolk glands, which provide a substance termed yolk, which serves as nourishment for the embryo. The fully formed eggs have shells and are “compound,” i.e., composed of the egg or ovarian cell, which is surrounded by numerous yolk cells or their products of disintegration. The two sexual openings usually lie close together, frequently in the fundus of a genital atrium; they are rarely separated from one another. Shell glands also usually occur (p. 221).

Reproduction is sexual, often, however, combined with asexual methods of propagation (segmentation, budding). The Platyhelminthes live partly free in fresh or salt water, exceptionally also on land. The greater part, however, live as parasites on or in animals.

CLASSIFICATION OF THE PLATYHELMINTHES.

Class I.--*Turbellaria* (or Eddy Worms). Flat worms for the most part, free living, and always covered with a ciliated epithelium.

Order 1.--Rhabdocœlida, gut unbranched.

Order 2.--Tricladida, gut with three main branches.

Order 3.--Polycladida, a central gut with lateral cæca. Development direct or through metamorphosis. They live in fresh and salt water or on land; very seldom as parasites.

Class II.--*Trematoda* (Sucking Worms[254]). [Usually known as Flukes.--F. V. T.] Flat worms, living as ecto- or endoparasites, that are only ciliated in the larval condition, and in their adult state are covered with a cuticle, the matrix cells of which lie in the parenchyma. They have either one, a few, or several suckers,[255] and frequently also possess chitinous fixation and adhesive organs. The intestine is single, but generally bifurcated, and not uncommonly there are transverse anastomoses between the forks or diverticula on them. Excretory organs double, with two orifices at the anterior extremity or a single one at the posterior end. Development takes place by a metamorphosis or alternation of generations (p. 283). These worms are almost always hermaphroditic, with two or more female and one male sexual orifice. They live, almost without exception, as parasites on vertebrate animals, but the intermediate generations are passed in molluscs.

[254] This grouping goes back to the year 1800, and was made by J. G. H. Zeder, a physician and helminthologist of Forchheim, who divided the helminths, which until 1851 were generally regarded as a special class of animals, into the groups of round, hook, sucker, tape and bladder worms, as which they are recognized up to the present time. In 1809, K. A. Rudolphi gave them the names Nematodes, Acanthocephali, Trematodes, Cestodes and Cystici.

[255] A sucker or acetabulum (little cup) is a round, cup-shaped muscular organ, the muscles of which are sharply defined from those of the body.

Class III.--*Cestoda* (Tapeworms). Endoparasitic flat worms without an alimentary canal. The larval stages are rarely ciliated, but are usually provided with six spines; the adult worm is covered with a cuticle, the matrix cells of which are embedded in the parenchyma. The body consists of a single segment (Cestodaria) or a chain of segments, in which case it consists of the scolex and the segments containing the sexual organs (proglottides) (Cestodes s. str.). The scolex is provided with various adhesive and fixation organs, and there are calcareous corpuscles in the parenchyma. Excretory organs symmetrical, opening at the posterior end. These worms are always hermaphroditic, and then possess one or two female and one male sexual orifice. During development a larval intermediate stage (“measle”) occurs and almost always in a different host to that in which the adult sexual worm lives. The adult stage is parasitic in vertebrate animals; but the larval stage may occur in invertebrates.

Class II. *TREMATODA*, Rud.

These worms are usually leaf- or tongue-shaped, but also barrel-shaped or conical; they vary from 0·1 mm. to almost 1 m.[256] in length; most of them, however, are small (5 mm. to 15 mm.). The surface on which the orifice of the uterus and the male sexual opening are situated is termed the ventral surface; the oral aperture, which also acts as anus, is always at the anterior end in the sub-order Prostomata (p. 230), but in the sub-order Gasterostomata it is ventral.

[256] Nematobothrium filarina, van Bened., on the branchial chamber of the Tunny.

Suckers are always present and occur in varying numbers and positions at the anterior extremities as well as on the ventral surface, and occasionally on the lateral margin and on the dorsum; the beginning of the intestine (mouth) is always surrounded by a sucker in the Prostomata.

In or near the suckers there may be chitinous hooks, claws or claspers, or the surface of the body is more or less covered with spines, scales or prickles; in one genus (Rhopalias) there are projectile tentacles beset with spines on the sides of the anterior part of the body.

The body of adult Trematodes is covered by a homogeneous layer of varying thickness, which either lies directly over the external layer (basement membrane) of the parenchyma, or over the muscles embedded in the parenchyma. This investing membrane (cuticle) arises from pear-shaped or spindle-shaped cells arranged singly or in groups (which lie between or internal to the diagonal muscles), and is connected with them by processes; these cells one may regard as epithelial cells which have sunk down, or possibly as parenchymatous cells. An epithelium of one layer is also found on the body of young stages, but it disappears during growth, and only occasionally do its nuclei persist until adult life. In its place we then find the cuticle, which, moreover, extends into all the body openings more or less deeply.

It is thus a debatable point whether the “investing layer” of flukes is a cuticle--that is, consists of modified epithelial cells--or whether it is a basement membrane, i.e., compressed and modified connective tissue cells; in this latter case the true epidermis and cuticle have been cast off. In the former case the epidermal cells are the pear-shaped cells referred to above. According to recent authors it consists of two parts, an outer true cuticle and an inner basement membrane. There are also unicellular cuticular glands, lying isolated or in groups, which are termed cephalic, abdominal, or dorsal glands according to the position of their orifice.

The PARENCHYMA is a connective substance, the structure of which is still a matter of dispute. It consists, according to some authors, of multipolar cells, the offshoots from which anastomose with each other so that a network, permeating the entire body and encompassing all the organs, is produced. There exists also, as part of it, a homogeneous matrix, in the form of lamellæ and trabeculæ that border small cavities communicating with each other and filled with fluid. According to other authors, the parenchyma of the Trematodes consisted originally of cells, of which, however, only the cell membranes remain, while the protoplasm has been liquefied except for small residua around the nucleus. Between these cells an intercellular mass has appeared. By partial absorption of the walls, adjoining spaces unite, and the originally flat cell walls become transformed into trabeculæ. According to this view the cavities filled with fluid are intra-cellular, according to the former view inter-cellular. Pigment cells occur only in a few species.

The MUSCULAR SYSTEM of the Trematodes is composed of (1) a dermo-muscular tube, (2) the dorso-ventral or parenchymal muscles, (3) the suckers, and (4) the special muscles of certain organs.

The dermo-muscular tube, which lies fairly close to the cuticle, consists of annular, diagonal, and longitudinal fibres which surround the entire body in one or several layers, and as a rule are more strongly developed on the ventral surface as well as in the anterior part of the body. The MUSCLES OF THE PARENCHYMA are found chiefly in the lateral parts of the body and pass through the parenchyma in a dorso-ventral direction; their diverging brush-like ends are inserted on the inner surface of the cuticle (fig. 120).

The suckers are specially differentiated parts of the dermo-muscular tube. Their concave inner surface is lined by the continuation of the cuticle and their convex external surface is covered by a more dense tissue that frequently takes the form of a refractive membrane, thus separating them from the parenchymal muscles.

The principal mass of the suckers consists of muscular fibres which run in three directions--equatorial, meridional and radial. The equatorial fibres correspond to the annular muscles, the meridional fibres to the longitudinal muscles, and the radial fibres to the muscles of the parenchyma; the radial fibres are always the most strongly developed. The function of these muscles is evident from their position; the meridional fibres flatten the suctorial disc and diminish the depth of its cavity, so that the internal surface may adhere to the object to be held; if the equatorial fibres now contract, the sucker rises by elongating longitudinally, and its inner surface is drawn in by the contraction of the radial muscles. Thus the sucking disc becomes adherent. Usually also there is a sphincter at the border of the suckers, which plays its part during the act of adhesion by constricting in a circular manner that part of the mucous membrane to which it is attached. The loosening of the fixed sucker is effected by relaxation chiefly of the radial fibres, by the contraction of the meridional fibres and certain bundles of muscles situated at the base and at the periphery of the suckers. The connective and elastic tissues between the muscles of the suckers probably also take part in the process.

Of the muscles of the organs which have developed from the parenchyma muscles we may briefly mention those bundles that are attached to certain parts of the genital apparatus, to the suckers, to the hooks and claws, and also, at all events in Fasciola hepatica, to the spines. The sheaths used for the projection of the tentacles of the Rhopaliadæ are also muscular.

The contractile elements consist of fibres of various lengths that are mostly parallel to one another, and frequently anastomose; a cortical substance finely fibrillated can usually be distinguished from an internal homogeneous mass; large nucleated cells of uniform size are always connected with them; these have been variously interpreted, but have been proved to be myoblasts, one or more of their processes constituting the muscular fibres.

The MOVEMENTS of the Trematodes consist in alterations of form and position of the body, as well as in creeping movements.

In the NERVOUS SYSTEM (fig. 121) can be distinguished a cerebral portion as well as strands (medullary strands) running from it, and peripheral nerves. The cerebral portion always consists of two large ganglia situated in the anterior end of the body which pass dorsally over the œsophagus and are connected by means of a broad and thick commissure composed of fibres only. From each ganglion three nerves run anteriorly--the inner and dorsal nerve for supplying the anterior dorsal part of the body; the median and ventral for the oral sucker; and the exterior and lateral likewise for the supply of the sucker.

In a similar manner three strands run backwards from each ganglion--one dorsal, one lateral and one ventral. The dorsal and ventral strands become united and curve backwards; the symmetrical lateral strands are connected by means of transverse commissures, the number of which vary according to the species. Such commissures also exist between the lateral and the two other strands on each side. There are ganglion cells along the entire course of the posterior cords, more particularly at the points of origin of the commissures. There also appears to be in addition a fourth anterior and posterior pair of nerves, the front pair for the oral sucker and the hind pair for the pharynx.

The peripheral nerves, which spring from the posterior strands as well as from the commissures, either pass directly to the muscular fibres or to the sensory cells that are situated at the level of the subcuticular cells, or they reach these after the formation of a plexus situated immediately beneath the dermo-muscular layer; the processes directed outwards terminate in small vesicles in the cuticle.

As to other ORGANS OF SENSE, simple eyes, two or four in number, are known in several ectoparasitic species as well as in a few free-living larval stages (Cercariæ) of endoparasitic forms. In the adult stage, however, they usually undergo complete atrophy.

The ALIMENTARY CANAL commences with an oral aperture, generally terminal or sub-terminal (ventral) at the anterior extremity, which leads into an oral cavity usually surrounded by a sucker; the œsophagus, of various lengths, is directed backwards and is generally surrounded by a muscular pharynx (fig. 122). In some cases there exists between the sucker and pharynx, pharyngeal pouches (præpharynx). Sooner or later the intestine divides into two lateral branches directed backwards, both of which end blindly (cæca) at the same level.[257] In many ectoparasites (Monogenea [p. 222]) a connection exists between the genital glands and one of the intestinal branches (ductus vitello-intestinalis [fig. 123]).

[257] The following conditions represent deviations from this type: (1) In Gasterostomum the oral aperture is situated in the middle of the ventral surface, and occasionally is even nearer to the posterior than to the anterior end. There is no proper oral sucker, but the pharynx is thus termed. (2) A few genera, such as Gasterostomum, Aspidogaster, Diplozoon, etc., have only one intestinal diverticulum, which is undoubtedly to be taken as representing the primitive condition, as it is also often found in the young stages of the Trematoda. (3) The branches of the intestines are curved and united behind (several Tristomidæ and Monostomidæ), while in Polystomum integerrimum (in the bladder of frogs) there are several commissures between the intestinal branches, and in the Schistosomidæ the united intestinal branches proceed as one channel towards the posterior end. (4) The termination of the two intestinal branches is not always on a level; they are therefore of different lengths. (5) When the œsophagus is very long the intestinal branches extend both forward and backward, so that the gut exhibits the form of an *H*. (6) In the broad and flat species the gut-forks form diverticula mostly externally but also internally; these again may branch (fig. 139). (7) In a few cases (Nematobothrium, Didymozoon) the intestine completely disappears up to the pharynx.

The oral cavity, pharyngeal pouches, pharynx, and œsophagus are lined with a continuation of the cuticle of the body; the gut cæca are lined with tall cylindrical epithelium (fig. 120). The œsophagus and intestinal branches often have also one layer of annular and longitudinal muscles; the pharynx has essentially the structure of a sucker (fig. 122).

The accessory organs of the alimentary canal consist of groups of unicellular SALIVARY GLANDS that discharge into the œsophagus in front of or behind the pharynx, or even into the pharynx itself.

The food of the Trematodes consists of mucus, epithelial cells, the intestinal contents of the hosts, and often also of blood, and this not only in those species living in the vascular system, but also in species living as ectoparasites or in the intestine or biliary passages of their hosts.

The final products of assimilation dissolved in the fluids of the body are distributed throughout the parenchyma and are thence expelled by a definite tubular system (excretory apparatus, proto-nephridia, formerly also termed the water-vascular system). This system, which is distributed throughout the entire body (fig. 124), is symmetrically developed, and, in the ectoparasitic Trematodes, it opens, right and left, at the anterior end on the dorsal surface; in all other flukes, however, it opens singly into the excretory pore (foramen caudale) at the centre of the posterior border; in those cases, however, where a sucker is present at the posterior end, as in the Amphistomata, the excretory pore is situated on the dorsal surface close in front of the sucker.

The EXCRETORY SYSTEM[258] consists of several parts: (1) of the more or less numerous terminal “flame” cells or funnel cells (figs. 124, 125); (2) of the capillaries ending in them; (3) of larger vessels receiving the capillaries; and (4) of the excretory bladder. Terminal cells and capillaries may be compared to unicellular glands with long excretory ducts; the cellular body (fig. 125) is comparatively large, stretched longitudinally, more rarely transversely, and provided with numerous processes, that are lost in the parenchyma; within is a conical cavity (analogous to the secretory cavity of unicellular glands) which is continued directly into the structureless capillary; at its blind end is a bunch of cilia projecting into the cavity, and which, during life, shows a flickering motion (ciliary flame). The nucleus is situated in the protoplasm of the terminal cell at its blind end.

[258] The following description relates in the main to the Distomata.

The entire apparatus thus begins blindly--i.e., within the terminal cells, to which must be ascribed the capacity of taking up from the fluid that permeates the parenchyma the products which are first collected into their own cavities and thence excreted by means of the capillaries and vessels.

The vessels possess definite walls, consisting of a membrane and a nucleated protoplasmic layer. They unite at many points on either side, and again pass into other canals (COLLECTING TUBES), which finally, travelling towards the posterior end, discharge into the excretory bladder (fig. 124).

The form and size of the bladder vary much according to the different species, but it always possesses its own flattened epithelium, surrounded by circular and longitudinal muscles, the circular muscles forming a sphincter around the opening. Frequently also the structure of the bladder extends to the tubules discharging into it, which therefore are not to be regarded as separate “vessels,” but rather as tubular diverticula of the bladder, directed anteriorly. In some few species the diverticula also branch and the branches anastomose, so that a network of tubules ensues which receives the vessels or capillaries. In such cases there are also ciliary tracts in the tubules.

The contents of the entire apparatus usually consist of a clear or sometimes reddish fluid; in some species there are larger or smaller granules, and occasionally also concretions occur.

Sexual Organs.--Nearly all the Trematodes are hermaphrodites, and only a few (Schistosomidæ, Koellikeria) are sexually differentiated. The sexual organs usually lie in the “central field” limited by the gut cæca; the vitellaria, on the other hand, are, as a rule, external to the gut cæca in the “lateral fields.”

The male apparatus[259] is composed of two variously formed testes (fig. 127) (globular, oval, indented, lobed, or ramified), which may lie side by side or one behind the other; from each testicle a tube (vas efferens) originates; sooner or later, both tubes as a rule unite to form the ejaculatory duct or vas deferens, which is frequently enclosed in a muscular CIRRUS SAC, or more rarely passes directly into the genital pore. The cirrus, which is the thick muscular terminal portion of the vas deferens, can be everted and protruded from the cirrus sac and serves as an organ of copulation. The walls of the muscular portion of the tube (the cirrus) are attached to the walls of the cirrus sac, and hence when the sac contracts the cirrus cannot be protruded except by evagination of its lumen. Opening into the middle portion of the vas deferens, and as a rule enclosed in the cirrus sac, is found a mass of unicellular glands (prostate), the vesicula seminalis (which is likewise within, or may also be outside the sac) being the dilated first portion of the vas.

[259] The following description relates mainly to the Distomata.

The female genitalia (fig. 126) consist of an ovary, usually situated in front of the testes, the form of which varies according to the species, the usually double vitellaria, the ducts and a number of auxiliary organs; the short oviduct directed towards the centre arises from the ovary, and is connected in the median line with the excretory duct of the vitelline glands. These grape-like glands possess longitudinal excretory ducts, which assume a transverse direction behind the ovary, unite together at the median line and form a single duct, often dilated into a vitelline receptacle, that unites with the oviduct. Near this point, moreover, there frequently opens a canal (Laurer’s canal) which begins on the dorsal surface, and on the inner end of which a vesicle filled with sperm (receptaculum seminis) usually occurs (fig. 126). Moreover, there are also numerous radial unicellular glands (shell glands) at or beyond the point of junction of the oviduct, vitelline ducts and Laurer’s canal. In this portion of the duct (oötype), which is usually dilated, the ovarian cells are fertilized, surrounded with yolk cells and shell material, and as ova with shells they pass into the uterus (a direct continuation of the oviduct), which, with its many convolutions, occupies a larger or smaller portion of the central field, and runs either direct to the genital pore or, forming convolutions, first runs posteriorly and then bends forward (descending and ascending limbs). In both cases the terminal part lies beside the cirrus pouch and discharges beside the male orifice either on the surface of the body or into a genital atrium. The terminal portion of the uterus, which is often of a particular structure, serves as a vagina (METRATERM).

The cirrus sac may include (1) the genital atrium (i.e., the common sinus, into which the vas deferens and vagina may open), or (2) a variable extent of the vas from cirrus to seminal vesicle. Thus the latter may be outside the sac. In the absence of a sac, the genital sinus may be surrounded by a pseudo-sucker, as in Heterophyes (in some cases the ventral sucker itself, from its close proximity to the genital pore, serves as an accessory copulatory organ). In other cases copulatory organs are formed by hooks projecting into the lumen of the terminal portion of the vas.

The GENITAL PORE, which is the opening from the genital sinus on to the surface, is generally situated at or near to the median line on the ventral surface and in the anterior region of the body; in most of the Distomata it is in front of the ventral sucker, in other cases, e.g., in the Cryptocotylinæ, it is behind.[260]

[260] The typical position of the genitalia is subject to many deviations, which are of importance in the differentiation of the genera and families. The following are some few of these deviations: (1) The genital pore remains on the ventral surface, but is situated beside or behind the ventral sucker, or it becomes marginal, and is then found in front of or beside the oral sucker, or at a lateral edge, or, finally, in the centre of the posterior border; the ducts also correspondingly alter their direction. (2) The ovary usually lies in front of the testes, not rarely, however, behind them or between them. (3) The three genital glands mostly lie together close in front of, or behind, the centre of the body; they may be moved far back, and may incidentally become separated one from the other. (4) The vitellarium may be single, in which case it then may lie in the central field. (5) A few forms possess but one, others several or numerous testes. Amongst the ectoparasitic trematodes there are also species with but one testis; but they mostly have several. As a rule, their uterus is short, but the oötype well developed. Special canals (vagina), single or double, are used for copulation, not the uterus. The vitelline ducts also communicate with the intestine through the canalis vitello-intestinalis (fig. 123).

The spermatozoa do not differ essentially in their structure from those of other animals; the ovarian or egg cells are cells without integument and contain a large nucleus and a little protoplasm; the vitellaria also produce nucleated cells, in the plasm of which there are numerous yellow yolk granules; the yolk cells detach themselves, like the ovarian cells, from the ovarium, and pass into the oviduct to surround each ovarian cell in the oötype. They disintegrate sooner or later in the completely formed egg and are utilized as food by the developing embryo.

DEVELOPMENT OF THE TREMATODES.

(1) Copulation.--Observation has demonstrated that the one or two vaginæ occurring in the ectoparasitic Trematodes are utilized as female organs of copulation, and that the copulation is cross; it is also known that Laurer’s canal, which was formerly generally regarded as the vagina, has only quite exceptionally, if at all, served the digenetic Trematodes as such--it appears to be homologous with the canalis vitello-intestinalis of the Monogenea[261]--but the terminal portion of the uterus, termed the metraterm, is used for copulation. Cross-copulation occurs as well as auto-copulation and auto-fecundation. The spermatozoa subsequently pass through the entire uterus, which is still quite short at the time the male organs are matured; the maturation of which, as usually is the case in hermaphrodites, precedes that of the female organs. It is only later with the onset of egg formation that the uterus is fully developed. Copulation, however, takes place also in the case of fully grown forms with completely developed uteri.

[261] Monogenea: Trematoda in which the anterior sucker, if present, is double. Development without an intermediate host.

(2) Formation of the Ova.--The ovarian cells arising from the ovary first become mature after their entry into the oötype by the formation of three polar bodies, fertilization then taking place. At the same time as the ovarian cell a number of yolk cells from the vitellarium and secretion, drop by drop, from the shell gland reach the oötype.[262] The shell is then formed during the generally active contractions of the oötype walls and then passes on into the uterus. In the uterus of the endoparasitic trematodes the eggs accumulate more and more, often in large quantities, while in ectoparasitic species generally only one or some few eggs can be found. The completed ova are of various forms and sizes. They are mostly oval, at all events in the digenetic trematodes, and the yellowish or brown shell is provided with an opening at one pole which is closed by a watch-glass-shaped lid (operculum). Appendages (filaments) on the shell--at one or both poles--are uncommon, but are the rule in the ova of the Monogenea (ectoparasitic species).

[262] [Recent work (e.g., Goldschmidt, Zool. Anzeiger, xxxiv, p. 482) has shown that the older views regarding the formation of the egg must be modified. In certain species, at any rate, the shell material is formed by the yellow droplets of the yolk glands and not by the so-called shell gland (Mehli’s gland) secretion, which is clear and watery. The function of this secretion accordingly still requires explanation; according to Looss it serves as a covering secretion for the egg-shell proper. It appears also that other granules, the yolk granules as distinct from the shell drop granules, are not always used up during the development of the embryo and hence do not function as yolk, so these also when they exist, and frequently they are wanting, must serve some other purpose, possibly that of imbibing water for the use of the embryo.--J. W. W. S.]

(3) Deposition of the Ova.--Soon after their formation, the Monogenea (ectoparasitic trematodes) deposit round the place of their attachment on the skin or the gills or other organs of their hosts, eggs which attach themselves by means of their filaments. The embryonic development thus takes place outside the parent. This also holds good for the eggs of many endoparasitic species, although as a rule in these the eggs are always retained for a longer time in the uterus. Moreover, they usually here undergo a part or a whole of their development, and are eventually deposited in those organs in which the adult forms are parasitic, but this is not always the case, as the egg, e.g., of F. hepatica appears in bile (and fæces) quite unchanged. By the natural passages they eventually get out of the body, and in cases where such do not exist, as in the case of the blood-vessels, the eggs pass out by means of the kidneys.

(4) The embryonic development, after irregular segmentation of the ovum into a number of blastomeres, leads to the formation of a solid blastosphere or morula, which is surrounded by a cellular investing membrane (yolk envelope), while the principal mass of the cells forms the embryo, which uses for its nourishment the yolk cells, which have in the meantime disintegrated (cf. footnote, p. 223). Usually, after the ova have reached water the embryos hatch out, leaving the yolk envelope in the egg-shell; in other cases, however, the embryos only hatch out after having been subjected to the influence of the intestinal juices, that is to say, in the intestine of an intermediate host which has ingested with its food the ova that have escaped from the primary host.

(5) The post-embryonic development of the Trematodes is accomplished in various ways; the process is the most simple in the ectoparasitic species (Monogenea), the young of which should certainly be regarded as larvæ, because they possess characteristics (cilia, simple gut, etc.) that are lacking in the adult worms, but which, nevertheless, pass into the adult state direct after a relatively simple metamorphosis. In the Holostomata,[263] a group found chiefly in the intestine of aquatic birds, and which rarely occur in other vertebrates, the ova develop in water. The young are ciliated all over, and, after having entered an intermediate host (leeches, molluscs, arthropods, amphibians, fishes) living in the water, they undergo a metamorphosis into a second larval stage; they then encyst and await transmission into the final host, where they become adult Metastatic trematodes, i.e., trematodes without asexually produced generations (p. 229).

[263] Holostomata: Prostomata with (in addition to the oral and ventral suckers) a third fixation apparatus, generally on a separate part of the body.

In the remaining so-called digenetic trematodes (p. 230) one or two asexual generations interpose between the miracidium and terminal stage, so that quite a number of adult worms may originate from one egg. Usually the young, which are termed MIRACIDIA[264] (fig. 129), hatch in water, where they move with the aid of their cilia. Sooner or later they penetrate into an intermediate host, which is always a snail or a mussel, and while certain of their organs disappear, they grow into a gutless germinal tube (SPOROCYST, fig. 131). These are simple elongated sacs with a central body cavity. They may or may not have excretory tubules. In these, according to the species, the larval stages (CERCARIÆ) that will ultimately become adult worms are produced, or another intermediate generation is first formed, viz., that of the REDIÆ[265] (figs. 132, 133), which are always provided with an intestine, and these then give rise to cercariæ (figs. 130, 134). The cercariæ, as a rule, leave their host and move about in the water with the assistance of their rudder-like tails. After a little time, however, they usually again invade an aquatic animal (worms, molluscs, arthropods, fishes, amphibians), then they lose their tails and become encysted (fig. 135); here they wait until they attain, together with their host, the suitable terminal host, and in this new situation they establish themselves and reach maturity. Or, again, the cercariæ may themselves encyst in water or on foreign bodies (plants) and wait until they are taken up directly by the terminal host, e.g., sheep.

[264] [Also known as ciliated embryos.--F. V. T.]

[265] [In Fasciola hepatica in the summer months the rediæ give rise to daughter rediæ, which then give rise to cercariæ.--J. W. W. S.]

Accordingly the following conditions are necessary for the completion of the entire development: (1) The terminal host in which the adult stage lives; (2) an intermediate host into which the miracidia penetrate and in which they become sporocysts; (3) a second intermediate host in which the cercariæ become encysted. In certain species, as in Fasciola hepatica, this second host is omitted, as the cercariæ spontaneously encyst on plants, or again (in other species) encystment may occur within the first intermediate host, when, in fact, the cercariæ (which in this case do not acquire an oar-like tail) do not swarm out of, but encyst themselves within their sporocysts. The development, moreover, may be further complicated by rediæ appearing in addition to the sporocysts, though this occurs in the first intermediate host and not in a second one.

Animals that harbour adult digenetic Trematodes thus become infected by ingesting encysted cercariæ, which either occur (1) in certain animals (second intermediate hosts) on which they feed, or (2) in water, or (3) on plants, or finally (4) in the first intermediate host; whereas animals harbouring encysted cercariæ have been directly infected by the corresponding tailed stage, and animals harbouring germinal tubes (sporocysts or rediæ) have been infected by the miracidia.

Thus certain species of ducks and geese become infected with Echinostoma echinatum by devouring certain water-snails (Limnæus, Paludina) in which the encysted cercariæ occur. Oxen become infected with Paramphistomum cervi (= Amphistomum conicum) by swallowing with water, cysts of this species which occur at the bottom of puddles and pits. Sheep are infected with Fasciola hepatica by eating grass to which the encysted cercariæ of the liver-fluke are attached; our song-birds infect themselves or their young with Urogonimus macrostomus by tearing off pieces containing the corresponding sporocysts which are full of encysted cercariæ from snails (Succinea amphibia), which act as the first intermediate hosts, and eating, or offering their young these pieces.

(1) The MIRACIDIA of the digenetic Trematodes are comparatively highly organized, and the mode of their formation from the segmentation cells of the ovum is only imperfectly known. They have a cuticular epithelium (fig. 129) entirely or partly covered with cilia, beneath this a dermo-muscular tube composed of circular and longitudinal muscles; also, a simple gut sac with an œsophagus, occasionally also with pharynx, salivary glands and boring spine, also a cerebral ganglion on which, in some species, there are eyes (fig. 131, a). As to the excretory organs, they are represented by two symmetrically placed terminal flame cells, with excretory vessels opening separately; there is a more or less ample (primary) body cavity between the parietes of the body and the gut; from the cellular parietal lining of this cavity single cells (germ cells) become free (fig. 131, a, b), and become rediæ or cercariæ.

[The germ cells of the miracidium and the germ balls of the sporocyst arise, according to some observers, by further division of undifferentiated blastomeres; according to others from the cells of the lining wall of its body cavity. It is from these free germ balls that the redia stage is developed.

[In the germ ball or morula appears an invagination, giving rise to the cup-shaped gastrula stage. This elongates and forms the REDIA (fig. 131, c).

[In the interior of the redia cells are budded off and develop into gastrulæ, as in the case of the sporocyst. These become a fresh generation of rediæ or give rise to the third stage (CERCARIA).]

(2) The SPOROCYSTS, on the contrary, which are produced direct from the miracidia, are very simple, as all the organs of the latter disappear, even to the muscles and excretory organs, during or after penetration into the intermediate host, whereas the budded and still budding cells of the wall of the (primary) body cavity continue to develop rapidly and form germ balls. The sporocysts when fully developed have the appearance of tubes or fusiform bodies with rounded edge; they are frequently of a yellow colour. Their length rarely exceeds a few millimetres; in some species their size increases exceedingly through proliferation, and they then occupy a large portion of the body of the intermediate host.

(3) The REDIÆ (figs. 132, 133), on the other hand, are more cylindrical and always have a simple intestine of varying length, provided with a pharynx; they likewise possess, situated near the circular ridge, a “birth pore” which serves for the exit of the cercariæ originating within them.

(4) The CERCARIÆ[266] are very different; typically they consist of the anterior body and the oar-like tail at the posterior end (fig. 134). The former, even to the genitalia, has the organization of the adult digenetic Trematodes, and thus allows the easy recognition of at least the characters of that large group to which the species in question belongs. On the other hand, however, there are also organs that are lacking in the adult form, such as, in many, the boring spine in the oral sucker, or the eyes situated on the cerebral ganglion; moreover, also, cutaneous glands (fig. 134), the secretion of which forms the cyst membrane. The oar-like tail may be long or short (stumpy-tailed cercaria) or entirely absent; its free end may be partly split (furcate cercaria), or split to its base (bucephalus); in various forms also the anterior end of the tail is hollow, and has enclosed within it the anterior body, which is otherwise free. The size also of the cercaria belonging to the different species is very diverse; in addition to forms swimming in the water that have the appearance of minute milky-white bodies, there are forms which measure as much as 6 mm. in length.

[266] The cercaria is the characteristic larval stage of the Trematodes, and corresponds to a cysticercus or cysticercoid, though there is the important difference that the cercaria has an enteric cavity. According to some observers the enteron is represented by the frontal sucker of some Cestodes, and by the rostellum of the majority of others.

The sporocyst and redia are regarded as intercalated stages, viz., as cercariæ exhibiting pædogenesis, i.e., development of young by a parthenogenetic process from individuals (i.e., cercariæ) not yet adult.

The encysted cercariæ (fig. 135) are globular or oval, and are surrounded by a homogeneous membrane, which may be striated or contain granules. The tail is always cast off when encystment occurs, and organs peculiar to the cercaria stage (boring papilla, eyes) almost entirely disappear. On the other hand, the genitalia appear or become more or less highly developed, in extreme cases to such an extent that they become functional, and after autocopulation the creatures produce ova within the cysts.

The cycle of development of the digenetic Trematodes has hitherto been generally explained as a typical ALTERNATION OF GENERATIONS, one sexual generation regularly alternating with one or two asexually reproducing generations. Recent authors, however, regard the cells in the sporocysts from which rediæ or eventually cercariæ arise as parthenogenetically developing ova, and the sporocysts as well as the rediæ as generations propagating parthenogenetically. In this case, however, it is an alternation of a sexual not with an asexual but with firstly a parthenogenetic generation (the sporocyst), the central cells of which are regarded as ova which develop parthenogenetically into the redia, and this the second parthenogenetic generation finally produces larvæ (cercariæ) capable of developing into the sexually mature form.

Other authors, again, regard the development of the Digenea as only a complicated metamorphosis (p. 283), which is distributed over several generations before it is concluded.

BIOLOGY.

Endoparasitic Trematodes, as fully developed organisms, occur in vertebrate animals only, with very few exceptions; they inhabit almost all the organs (with the exception of the nervous and osseous systems and the male genitalia), but by preference the intestine in all its extent from the oral cavity to the anus; and, further, certain species or groups inhabit only quite restricted parts of the intestine. Besides in the intestine other species live in the liver, or in the bile-ducts, or in the gall-bladder; other accessory organs of the intestine, such as the pancreas, bursa Fabricii (of birds), are only infected by a few species. Many inhabit the lungs, or the air sacs in fowls, a few the trachea. Trematodes have also been known to occur in the urinary bladder, the urethra and the kidneys of all classes of vertebrates; they are also present in the vascular system of a few tortoises, birds and mammals; in birds they even penetrate from the cloaca into the oviducts, and are occasionally found enclosed in the laid eggs; one species is known to occur in the cavum tympani and in the Eustachian tube of a mammal (Dugong), another in the frontal sinus of the polecat; several species infest the conjunctival sac under the membrana nictitans of birds, one species even lives in cysts in the skin of song-birds. In an analogous manner the ectoparasitic Trematodes are not entirely confined to the surface of the body or the trachea of the lower vertebrate animals; a few species appear exclusively in the urinary bladder, in the œsophagus, and in the case of sharks in an accessory gland of the rectum.

Trematodes live free and active within the organs attacked, though they may attach themselves by suction for a longer or shorter period; in other cases, however, they bore more or less deeply into the intestinal wall with their anterior end, or lie in cysts of the intestinal wall which only communicate with the lumen through a small opening; in those species living in the lungs of mammals the host likewise produces a cyst, which usually encloses two specimens; such association of a pair is also observed in other situations, and, though this is the rule in species sexually distinct, it is not entirely confined to these.

As regards the AGE attained by endoparasitic Trematodes, there are but few reliable records, and these differ considerably; the overwhelming majority of species certainly live about a year, or perhaps a little longer, but there are some whose term of life extends to several or many years.

Trematodes are but rarely found encysted in the higher vertebrate animals; the condition, however, is more frequent in amphibians, and especially in fishes, as well as in numerous invertebrate animals.

CLASSIFICATION OF THE TREMATODES OF MAN.

The following classification, partly artificial, partly natural, embraces only the flukes found in man:--

Order. *Digenea*, v. Beneden, 1858.

Anterior sucker single and median, present. Eggs few. The (specialized) terminal portion of the uterus serves as a vagina. Development indirect, i.e., an intermediate host is required.

Sub-order. *Prostomata*, Odhner, 1905.

Mouth surrounded by the anterior sucker.

Group. *Amphistomata*, Rudolphi, 1801, ep., Nitzsch, 1819.

Gut forked, two suckers, the posterior sucker (acetabulum) terminal or ventro-terminal behind the genitalia, or at most embraced by the vitellaria. Skin with no spines. Excretory bladder a simple sac opening dorsally near hind end. Testes in front of ovary. Genital pore, median in anterior third of body. Thick flukes, almost circular in cross section.

Family. *Paramphistomidæ*, Fischoeder, 1901.

Amphistomata: Body not divided into a conical anterior portion and disc-like caudal portion. Ventral pouch absent.

Sub-family. *Paramphistominæ*, Fisch., 1901.

Paramphistomidæ: Oral sucker without evaginations. Not in man.

Sub-family. *Cladorchiinæ*, Fisch., 1901.

Paramphistomidæ: Oral sucker with evaginations; testes, two, deeply cleft (fig. 137). Genera: Watsonius, Cladorchis, etc.

Family. *Gastrodisciidæ*, Stiles and Goldberger, 1910.

Amphistomata: With body divided into a conical cephalic and disc-like caudal portion (fig. 138). Posterior sucker ventro-terminal. Oral sucker with evaginations. Genera: Gastrodiscus and Homalogaster.

Group. *Distomata*, Retzius, 1782.

Gut forked, two suckers, the posterior sucker (acetabulum) ventral. It is always separated from the hind end by at least a part of the genitalia.

Family. *Fasciolidæ*, Railliet, 1895.

Large flat forms, genital pore in front of ventral sucker, the latter powerful. Vitellariæ of numerous follicles, united by branching vitellarian ducts, at the sides of the body meeting posteriorly and extending ventrally and dorsally. Cirrus and vagina without spines. No crown of strong spines around sucker. Testes much branched. Uterus not well developed. Excretory bladder much branched. Eggs large.

Sub-family. *Fasciolinæ*, Odhner, 1910.

Large or median forms, gut much branched. Body has a shoulder separating head from body. Receptaculum seminis absent. Ovary branched, ventral sucker in anterior part of body. Genus: Fasciola.

Sub-family. *Fasciolopsinæ*, Odhner, 1910.

Shoulder absent. Receptaculum seminis present. Ovary branched, gut takes a zig-zag course with kinks on it, ventral sucker in anterior part of body. Genus: Fasciolopsis.

Family. *Opisthorchiidæ*, Braun, 1901, emend. auctor.

Ovary in front of testes. Small to medium flukes, very transparent, tapering anteriorly. Vitellaria moderately developed not extending in front of sucker. Cirrus absent. Seminal vesicle a twisted tube free in parenchyma. Testes near hind end one behind the other, lobed or branched, but not dendritically. Excretory bladder *Y*-shaped, the two limbs short, the stem *S*-shaped passing between the testes. Receptaculum seminis well developed. Laurer’s canal present. Uterine coils transverse, numerous. Eggs small.

Sub-family. *Opisthorchiinæ*, Looss, 1899, emend. auctor.

Opisthorchiidæ in which the excretory pore is terminal. Excretory bladder long, dorsal to testes. Uterine coils not overlapping gut forks. Genera: Opisthorchis, Paropisthorchis, Clonorchis, Amphimerus, etc.

Sub-family. *Metorchiinæ*, Lühe, 1909.

Opisthorchiidæ in which the excretory pore is ventral. Excretory bladder short, ventral to testes. Uterine coils partly overlapping gut forks and extend anteriorly beyond the sucker. Vitellaria compressed on the sides of the body. Genus: Metorchis.

Family. *Dicrocœliidæ*, Odhner, 1910.

Ovary behind testes. Testes behind the ventral sucker, between it and the ovary. Body thin and transparent. Cirrus sac encloses the pars prostatica and seminal vesicle. Skin smooth. Gut forks do not reach posterior end. Receptaculum seminis and Laurer’s canal present. Vitellaria, moderate, lateral in mid-body slightly overlapping the gut. Uterus with an ascending and descending branch and numerous transverse coils extending to hind end. Eggs dark brown, 25 µ to 60 µ. Excretory bladder tubular in posterior third or half of body. Parasitic in bile-ducts of mammals and birds. Genus: Dicrocœlium.

Family. *Heterophyiidæ*, Odhner, 1914.

Ovary in front of testes. Genital pore behind or on a level with ventral sucker. Genital pore surrounded by a pseudo-sucker (i.e., its muscle is not sharply separated from but blends with the body muscles). Cirrus sac absent, consequently vesicula seminalis and pars prostatica lie free. Vagina and ejaculatory duct unite into a common duct before opening. Small and very small forms. Body covered with scales. Genera: Heterophyes, Metagonimus, etc.

Family. *Troglotremidæ*, Odhner, 1914.

More or less flattened Distomes of compact form, 2 to 13 mm. long. Ventral surface flat or somewhat hollowed, dorsal surface arched. Skin completely covered with pointed spines. Musculature weakly developed also in the suckers in those forms that inhabit cysts. Gut with pharynx and a not very long œsophagus and cæca, which end more or less shortly before the hind end. Excretory bladder *Y*-shaped or tubular. Pars prostatica and seminal vesicle always distinct. Testes elongated, symmetrically placed in or behind the middle of the body. Ovary directly in front of the testes, right-sided, generally much lobed. Receptaculum seminis and Laurer’s canal present. Vitellaria generally well developed, exclusively or for the most part confined to the dorsal surface, leaving only a median band unoccupied. Uterus either very long, coiling here and there, or shorter and more convoluted. Eggs in first case small 17 µ to 25 µ, in the second much larger 63 µ to 85 µ or even 120 µ (?) long. Parasitic in carnivora or birds, generally occurring in pairs in cyst-like cavities. Genera: Paragonimus, Pholeter, Collyriclum, Troglotrema.

Family. *Echinostomidæ*, Looss, 1902.

More or less elongated flukes, small or very large, much flattened anteriorly, less so posteriorly, or even round. Suckers near one another, the anterior small and weak, the posterior large and powerful directed obliquely backwards. Surrounding the oral sucker dorsally and laterally but not ventrally is a fold or “collar” bearing a row or rows of pointed spines which are continued round laterally on to the ventral corners, the number being constant for each species, the corner spines large or specialized, skin anteriorly scaled or spiny. Alimentary canal consists of a pharynx, epithelial “pseudo-œsophagus” and gut cæca reaching to posterior end. Testes behind one another in hind body. Ovary on right side or median directly in front of the testes. Vitellaria lateral, usually extending to the hind end and not beyond the ventral sucker anteriorly. Genital pore just in front of ventral sucker. Uterus in transverse loops. Genital sinus absent or present. Receptaculum seminis and Laurer’s canal present. Eggs thin shelled and large, bright yellow, 65 µ to 120 µ long. Excretory bladder *Y*-shaped. Parasitic in gut of vertebrates, especially birds.

Sub-family. *Echinostominæ*, Looss, 1899.

Cirrus sac usually reaching to centre of ventral sucker, but not beyond. Cirrus long, usually without spines, coiled when retracted. Seminal vesicle tubular, twisted. On the head a ventral uniting ridge between the angles of the collar. Dorsal circlet of spines, single or double, not interrupted unless the collar itself is dorsally divided. Genera: Echinostoma, etc.

Sub-family. *Himasthlinæ*, Odhner, 1910.

Cirrus sac reaching far beyond ventral sucker. Cirrus armed with strong rose-thorn-shaped hooks. Vesicula seminalis tubular not coiled. Cervical collar not continued across ventral aspect. Spines on collar in one row. Body armed with fine needle-shaped spines.

Family. *Schistosomidæ*, Looss, 1899.

Sexes separate. Genital pore behind the ventral sucker. Ventral sucker elevated above the surface. Pharynx absent. Gut forks reunite to form a single stem. In ♂ four or more testicular follicles. In ♀ a single ovary, just in front of the union of the gut forks. Vitellaria on either side of the united gut stem.

THE TREMATODES OBSERVED IN MAN.

Family. *Paramphistomidæ*, Stiles and Goldberger, emend. 1910.

Sub-family. *Cladorchiinæ*, Fisch., 1901.

Genus. *Watsonius*, Stiles and Goldberger, 1910.

Cladorchinæ.--Body pyriform. Ventral pouch absent. Acetabulum ventral or (?) ventro-subterminal, very large, margins projecting, aperture small. Genital pore in front of bifurcation of gut, not surrounded by a sucker; ductus hermaphroditicus apparently absent. Excretory pore at posterior end of excretory vesicle, behind Laurer’s canal. Oral sucker with a pair of irregularly globular suctorial pouches; œsophagus thickened distally; cæca long, not wavy; end in acetabular region.

Male Organs.--Testes two lobed, smaller than acetabulum; longitudinally, nearly or quite coinciding; transversely they abut or slightly overlap; preovarial in equatorial and caudal thirds. Pars musculosa not largely developed; cirrus pouch absent.

Female Organs.--Ovary and shell gland post-testicular. Vitellaria extend from gut fork to slightly beyond gut ending; uterus intercæcal, partly post-testicular. Laurer’s canal in front of excretory vesicle.

Type Species.--Watsonius watsoni, Conyngham, 1904.

*Watsonius watsoni*, Stiles and Goldberger, 1910.

Syn.: Amphistomum watsoni, Conyngham, 1904; Cladorchis watsoni, Shipley, 1905.

Body, 8 to 10 mm. long, by 4 to 5 mm. broad, by 4 mm. thick; tapers anteriorly to 2·5 mm. Caudal extremity bluntly rounded, venter surrounded by an elevated ridge, surface with transverse ridges best defined ventrally. Genital pore median about one-quarter of body length from anterior end at level of suctorial pouches. Acetabulum 1 mm. in diameter, margin projecting, aperture small. Mouth in a groove with digitate papillæ. Oral sucker very large, one-fifth of length of body, with a pair of irregularly globular pouches. Œsophagus somewhat longer than sucker. Excretory pore at the level of the acetabular aperture. The vesicle extends from the plane of the transverse vitelline ducts to centre of acetabulum.

Male Organs.--Testes deeply notched adjoining one another. Vesicula seminalis much coiled and dilated, pars musculosa not coiled. Pars prostatica (?) dilated, ejaculatory duct long and narrow, opening on a papilla; genital atrium papillated.

Female Organs.--Ovary dorso-posterior of posterior testis. Shell gland dorsal to ovary. Vitellaria ventral and lateral to gut cæca extending from gut fork to equator of acetabulum. Uterus dorsal to testes, ductus hermaphroditicus absent. Laurer’s canal opens in dorso-median line slightly behind anterior border of sucker.

Eggs.--123 µ to 133 µ long by 75 µ to 80 µ broad.

Habitat.--Jejunum and duodenum of man, German West Africa. The parasite has only been found once in man. The patient, a negro from German West Africa, died at Zola, Northern Nigeria. The symptoms were persistent watery diarrhœa without blood or mucus. The parasites were also passed in the stools. It occurs also in monkeys.

Family. *Gastrodisciidæ*.

Genus. *Gastrodiscus*, Lkt., 1877.

Acetabulum small, caudal and ventral margin raised, aperture relatively large. Genital pore without sucker. Excretory pore post-vesicular, posterior to opening of Laurer’s canal. Œsophagus with muscular thickening; cæca not wavy, long, end post-equatorial and post-testicular.

Male Genitalia.--Testes two, branched pre-ovarial.

Female genitalia.--Ovary and shell gland post-testicular. Vitellaria extracæcal; uterus intercæcal; Laurer’s canal entirely prevesicular.

Type.--Gastrodiscus ægyptiacus, Cobbold, 1876.

*Gastrodiscus hominis*, Lewis and McConnell, 1876.[267]

Syn.: Amphistomum hominis, Lew. and McConn.

[267] Leiper places this species in a new genus Gastrodiscoides. Genus Gastrodiscoides, Leiper, 1913, distinguished from Gastrodiscus by: (1) large genital cone; (2) position of genital orifice; (3) disc without papillæ; (4) testes one behind the other.

Body, reddish in the fresh, 5 to 8 mm. long; posteriorly, 3 to 4 mm. broad. The disc has incurved edges which are interrupted in front where it joins the anterior cylindrical portion and posteriorly behind the ventral sucker. The disc itself and ventral surface are covered with a number of (microscopic) papillæ. Pharynx provided with two diverticula or pouches. The bifurcation of the gut lies sometimes above, sometimes below the level of the genital pore. The gut cæca end about the level of the centre of the acetabulum.

Genital Pore.--About the middle of the conical anterior portion. (It appears to be surrounded by a muscular sucker.) Leiper (1913) describes the ducts as discharging at the tip of a large fleshy papilla, the surface of which bears cuticular bosses.

Testes much lobed, the anterior is smaller than the posterior and lies at about the level where the anterior conical portion joins the disc. The posterior testis just in front of the anterior margin of the acetabulum separated from it by the ovary. The ovary, somewhat oval in shape or slightly constricted in the middle, lies slightly to the right of the median line. Dorsal to it lies the well-developed shell gland, Laurer’s canal opening in front of the excretory bladder. The excretory bladder is a long sac with its opening at its posterior extremity about the level of the middle of the acetabulum. The vitellaria are restricted in extent. They do not extend forward beyond the anterior border of the posterior testis. They are best developed in the area between the acetabulum and the termination of the gut cæca.

The eggs are oval and measure 150 µ in length by 72 µ in breadth.

Habitat.--Cæcum and large intestine of man. Also in the pig (5 per cent.) in Annam.

Distribution.--This parasite has been recorded from Assam (not uncommon), British Guiana (Indian immigrants), and Cochin China.

Gastrodiscus ægyptiacus, Cobbold, 1876, and G. secundus, Looss, 1907, occur in the horse; G. minor, Leiper, 1913, in the pig in Nigeria and Uganda.

Family. *Fasciolidæ*, Raill., 1895.

Sub-family. *Fasciolinæ*, Odhner, 1910.

Genus. *Fasciola*, L., 1758.

The ventral sucker is situated at the level of the junction of the cone with the body, viz., at the level of the “shoulder,” and is large and powerful. The cuticle is covered with strong spines; the gut cæca run in the mid-line to the hind end, and are provided with numerous long lateral and fewer and shorter median branches. The ovary lies on one side in front of the transverse vitelline duct; the testes lie obliquely one behind the other. The uterus, in the shape of a rosette, lies in front of the genitalia. Laurer’s canal is present; the vesicula seminalis lies in the cirrus pouch; the ova are large, not very numerous, and only develop after they have been deposited. Parasites of the biliary ducts of herbivorous animals.

*Fasciola hepatica*, L., 1758.

Syn.: Distomum hepaticum, Retz., 1786; Fasciola Humana, Gmel., 1789; Distomum caviæ, Sons., 1890; Cladocœlium hepaticum, Stoss., 1892.

Length 20 to 30 mm., breadth 8 to 13 mm., cephalic cone 4 to 5 mm. in length and sharply differentiated from the body by a shoulder on each side. Spines in alternating transverse rows and extending on the ventral surface to the posterior border of the testes, and on the dorsal surface not quite so far. The spines are smaller on the cephalic cone than on the posterior part of the body, where they are discernible with the naked eye. The suckers are hemispherical, and near each other; the oral sucker is about 1 mm. and the ventral sucker about 1·6 mm. in diameter. The pharynx, which includes almost the entire œsophagus, measures 0·7 mm. in length and 0·4 mm. in breadth. The intestine bifurcates at the limit of the cephalic cone and the branches are even here furnished with diverticula directed outwardly. The ovary is ramified and situated in front of the transverse vitelline duct, usually on the right side; the shell gland lies near the ovary in the median line; posterior to the transverse vitelline ducts are the greatly ramified testes, which occupy the greater portion of the posterior part of the body, with the exception of the lateral and posterior border; the long vasa efferentia only unite as they enter the cirrus pouch. The vitellaria occupy the sides of the posterior part of the body, commencing at the level of the ventral sucker and uniting behind the testes. The ova are yellowish-brown, oval, operculated, 130 µ to 145 µ in length, 70 µ to 90 µ in breadth (average size 132 µ by 70 µ).

The Liver Fluke inhabits the bile-ducts of numerous herbivorous mammals (sheep, ox, goat, horse, ass, rabbit,[268] guinea-pig, squirrel, beaver, deer, roe, antelope, camel, kangaroo, and others), and is distributed over the whole of Europe, though not to an equal extent. It is further known in North Africa, in North and South America, as well as in Australia; it is also found in Asia, as it has been reported from Japan, China, and Tonkin (Gaide, two cases in man). In some districts of Germany it is very frequent, and the slaughter-house statistics of various places show that it is of daily occurrence. Fasciola magna occurs in herbivora in America.

[268] [There does not seem to be any direct evidence of either rabbits or hares normally being invaded by this fluke.--F. V. T.]

The liver fluke, however, is by no means a harmless parasite, for it produces in domestic animals, more especially in sheep, a disease of the liver that appears epidemically in certain years and districts, and commits great ravages amongst the flocks.

[The following records show the enormous loss caused in sheep by this parasite. In 1812, in the Midi, principally in the Departments of the Rhône, Herault, and Gard, the disease was rampant; 300,000 sheep perished in the Arles territory, and 90,000 in the Arrondissements of Nîmes and Montpellier. In 1829 and 1830, in the Department of the Meuse and near localities, not only sheep but oxen died in enormous numbers; for instance, in the Arrondissement of Verdun out of 50,000 sheep 20,000 died, and out of 20,000 cattle 2,200 died. In England, in 1830, 2,000,000 sheep were carried off; whilst in 1862 60 per cent. of the sheep died in Ireland; and in 1879 over 300,000 were lost in England; whilst as late as 1891 one owner in the same country lost over 10,000 sheep (Live Stock Journal, October 30, 1891).--F. V. T.]

The disease usually commences towards the end of summer with an enlargement of the liver, induced by the invasion of numerous young flukes; in the autumn and winter the animals suffer from the consequences of disordered biliary secretion; they become feverish, emaciated, and anæmic, and lose their appetite. In consequence of the consecutive atrophy of the liver, œdema and ascites set in, and many animals succumb to this “liver rot.” On examination the liver is found to be shrunken, the bile-ducts are enormously dilated and in parts saccular and full of flukes. Should the animals survive this stage, spontaneous recovery ensues in consequence of the flukes commencing to leave the liver in the spring, but the liver remains changed and its sale is prohibited[269] when the changes are extensive.[270]

[269] [This is not the case in Great Britain; fluky sheep are sent to market, there being no danger to man from eating the flesh.--F. V. T.]

[270] As an example, this occurred in Berlin in the case of 19,034 oxen, 15,542 sheep, 1,704 pigs, and 160 calves in the period of 1883–1893; during which time 719,157 oxen, 1,519,003 sheep, 2,258,110 pigs, and 567,964 calves were slaughtered. As a matter of fact, however, the number of infected beasts was really larger.

[The following stages may be noticed in sheep suffering from fascioliasis. Gerlach recognized four stages, based on the varied relations that the flukes contract with the liver of their host. These periods are sometimes very marked, but at others, owing to subsequent infections, the features become merged and so obliterated. But when a single infestation occurs they are very marked.

[The first period is called the PERIOD OF IMMIGRATION. This occurs at the fall of the year and generally passes unperceived, as the young flukes do little harm to the liver. It varies from four to thirteen weeks. Gerlach has remarked upon cases of death from apoplexy at this period.

[The second period is the PERIOD OF ANÆMIA. This occurs in November and December. The sheep at first fatten rapidly, but later the mucous membranes become pale and of a yellowish hue, and the sheep become sluggish and cease to feed. The fæces are normal, but may contain fluke ova.

[The third period is the PERIOD OF WASTING. This corresponds with the beginning of January--about three months after the entry of the larvæ. Emaciation now becomes very marked, the skin and mucous membranes blanched, temperature variable and marked by an irregular curve; respiration laboured and quick; appetite regular; abortion frequently occurs in pregnant ewes; pressure on the back causes the animals to fall; local œdemas occur, the most perceptible in the submaxillary space, extending below the larynx and over the cheeks and parotids (called “bourse,” “boule” in France; “watery poke” or “cockered” in England). Death usually occurs at this period, but a fourth stage may occur.

[The fourth period is the PERIOD OF MIGRATION OF THE FLUKES. This is a period of convalescence and recovery, generally in May and June.--F. V. T.]

Oxen suffer less in general, but even in these animals “stray” hepatic flukes are occasionally found in the lungs, enclosed in thick-walled cysts.

Pathological Anatomy.--The bile-ducts are conspicuous on the surface of the liver. They are thickened and much dilated and in parts saccular, and considerable atrophy of the liver cells accompanies the condition. Histologically there is immense proliferation of the epithelium of the bile-ducts leading to “adenomata.”

The LIFE-HISTORY of the liver fluke was discovered by R. Leuckart and P. Thomas. According to these investigators the elongated miracidium (fig. 131, a) ciliated all over develops from the eggs a few weeks after the latter (fig. 142) have reached the water, and after it has become free the embryo penetrates and becomes a sporocyst (fig. 131, b) in a water-snail (Limnæus truncatulus, Müll. = L. minutus, Drap.) that is common in fresh water, and can live in the smallest collection of water as well as in fields that have been flooded. The sporocyst first of all produces rediæ, which remain in the same host (and under certain circumstances, e.g. in summer, these develop a second generation of rediæ), and these finally form cercariæ (fig. 134). The latter become encysted on blades of grass and are taken up by the respective hosts with their food; this takes place towards the end of summer, while the sheep feeding on the pasture land in the spring spread the eggs of the fluke, and sometimes the fluke itself, by passing them with their fæces.

In districts where Limnæus truncatulus is absent, analogous species act as the intermediary hosts, of which one example according to Lutz is Limnæus oahuensis in the Sandwich Islands.

[The host in Europe is Limnæus truncatulus. This snail extends from Siberia to Sicily and Algeria, and according to Captain Hutton is a native of Afghanistan. It also occurs in Thibet, Amoor, Morocco, Tunis, Canary Islands and the Faroe Islands. It deposits its eggs or spawn upon the mud around ponds, ditches and streams. The eggs are laid in batches of thirty to a hundred, each snail laying as many as 1,500 eggs; they are united into strips of a gelatinous substance. In about two weeks young snails appear. It is amphibious, being more frequently met with out of the water than in it. It occurs in elevated spots as well as in low-lying districts. Moquin-Tandon found it at 4,000 feet in the Pyrenees. In the allied species, L. peregra, the fluke will develop up to a certain stage, but never completes all its varied phases.

[In South America the host is probably Limnæus viator, Orb., and in North America Limnæus humilis, Say.--F. V. T.]

In human beings as well as in some of the mammals quoted above, the liver fluke is only a casual parasite, and hitherto only twenty-eight cases have been observed in man; the infection was mostly a mild one and there were no symptoms, or only very trifling ones; a few isolated cases were only discovered post mortem. Occasionally, however, even when the infection was inconsiderable, severe symptoms were set up, which in isolated cases led to death. The symptoms (enlargement and painfulness of the liver, icterus) merely pointed to a disease of the liver.

Diagnosis can only be established by finding eggs in the fæces. Care should be taken not to confuse them with those of Dibothriocephalus latus.

HALZOUN.

In North Lebanon, the liver fluke is, according to A. Khouri, a frequent parasite of man, not in the liver, however, but in the pharynx. The occurrence in this unusual site is effected by the eating of raw infected livers, especially those of goats (Capra hircus). The flukes thus taken in do not all reach the stomach, where they would be soon killed, but some of them attach themselves to the pharyngeal mucosa and to the adjoining parts, and there cause inflammation and swelling, which lead to dyspnœa, dysphagia, dysphonia and congestion of the head, sometimes even to still more severe symptoms, and even death. The affection termed “Halzoun” lasts some hours or several days, and after vomiting recovery sets in. In other cases man becomes infected in the usual way by ingesting cysts attached to grass or the underside of leaves of plants (e.g., Rumex sp.), where they are overlooked from their scanty size (0·2 to 0·3 mm.).

As the liver fluke feeds on blood it is possible that it also reaches, particularly when young, the circulatory system, and cases have been known in which it has been carried by the blood into organs far from its original situation. Such cases also have been repeatedly observed in men. Probably the parasite described by Treutler, 1793, as Hexathyridium venarum, which protruded from the ruptured anterior tibial vein of a man, was a young liver fluke. A few adult specimens were found by Duval in the portal and other veins post mortem at Rennes (1842) in a man, aged 49, and a similar statement is reported by Vital from Constantine (1874). Giesker, in 1850, found two hepatic flukes in a swelling on the sole of the foot of a woman. Penn Harris states that he observed six specimens in Liverpool in a spontaneously ruptured abscess of the occiput of a two months old infant. Another case which, like the previous one, is reported by Lankester,[271] relates to a sailor who suffered from an abscess behind the ear, and from which a liver fluke was expelled. Finally, Dionis de Carrières reports the case of a man, aged 35, in whose right hypochondriac region a tumour the size of a pigeon’s egg had formed, and from which a young liver fluke was extracted.

[271] In the English translation of Küchenmeister’s work on Parasitology (London, 1857). The specimen is preserved in the Hunterian Museum, London, and is an adult liver fluke, measuring 18 mm. in length and 7 mm. in breadth.

From such records it is not impossible that Distomum oculi humani, Ammon, 1833, as well as Monostomum lentis, v. Nordm., 1832, may have been very young hepatic flukes that had strayed. Ammon found four specimens (length 0·5 to 1 mm.) of his species (named Distomum ophthalmobium by Diesing in 1850) between the opaque lens and the capsule of a five months old child in Dresden, and von Nordmann discovered his Monostomum lentis to the number of eight specimens (only 0·3 mm. in length) in the opaque lens of an old woman. Minute white bodies which Greef found in the cortex of the lens of a fisherman, aged 55, removed on account of cataract, were with some reserve regarded as Trematode larvæ. The fact that Ammon found that the intestinal cæca of the worm discovered by him had no lateral branches does not negative the above opinion, as in the liver fluke the intestinal cæca are originally unbranched, and according to Lutz they only develop lateral ramifications later, between the twelfth and twenty-second day of infection (fig. 144).

*Fasciola gigantica*, Cobbold, 1856.

Syn.: Distomum giganteum, Diesing, 1858; Fasciola gigantea, Cobbold, 1858; Cladocœlium giganteum, Stoss., 1892; Fasciola hepatica var. angusta, Raill., 1895; Fasciola hepatica var. ægyptiaca, Looss, 1896.

This species is closely allied to Fasciola hepatica, but is distinguished by its elongated body, short cephalic cone, almost parallel sides, larger ventral sucker, which is also closer to the oral sucker, and by its larger eggs. Length up to 75 mm., width up to 12 mm. Oral sucker 1 to 1·2 mm., ventral sucker up to 1·7 mm. in diameter. Eggs 150 µ to 190 µ long by 75 µ to 90 µ broad.

Habitat.--Bile-ducts of Camelopardalis giraffa, Bos taurus, Bos indicus, Bos bubalis, Ovis aries and Capra hircus.

Distribution.--Africa.

This species has once been observed in man by Gouvea, in Rio de Janeiro, in a French naval officer who became ill with fever, cough and slight blood-spitting. The lungs were normal except for a sharply circumscribed spot at the base of the left lung. Twenty days later during a fit of coughing the patient spat up a fluke 25 mm. long, characterized by its slender aspect and by the size of its ventral sucker, and its close proximity to the oral sucker. Considering the fact that Gouvea’s patient had spent many weeks in July of the same year in Dakar (Senegambia), where according to Railliet Fasciola gigantica is common in slaughtered animals, and considering also the characters of the fluke, Railliet rightly assumes that one had to do with the African giant fluke and that the patient had infected himself in Dakar.

Sub-family. *Fasciolopsinæ*, Odhner, 1910.

Genus. *Fasciolopsis*, Looss, 1898.

Ventral sucker large, and elongated posteriorly into a sac. Cirrus pouch long and cylindrical, its greatest length being occupied by the sinuous tubular seminal vesicle, on which exists a peculiar cæcal appendage. Laurer’s canal present.

*Fasciolopsis buski*, Lank., 1857.

Syn.: Distomum buski, Lank., 1857; Dist. crassum, Cobbold, 1860, nec v. Sieb., 1836.

The length of the body varies; it may measure 24 to 37 or even attain 70 mm.; the breadth is from 5·5 to 12 to 14 mm. In the pig the fresh parasites measure, smallest, 12 to 8 mm.; largest, 35 to 16 mm. (Mathis and Léger). Skin without spines, but according to Heanly always present in man and pig specimens. The oral sucker measures 0·5 mm. in diameter; the ventral sucker is three to four times as large; the pharynx is globular, 0·7 mm. in diameter; the prepharynx is provided with a sphincter; the intestinal cæca extend to the posterior border with two characteristic curves, one at the anterior border of the anterior testis, the other between the two testes. The genital pore is at the anterior border of the ventral sucker; the cylindrical cirrus pouch extends from behind the ventral sucker to half-way to the shell gland. The seminal vesicle extends forwards within the cirrus pouch as a convoluted tube. From its anterior portion is given off the cæcal appendage, which has itself short lateral diverticula. It runs backwards, ending blindly about 0·5 mm. from the posterior end of the cirrus sac. The seminal vesicle is continued as the pars prostatica (?) 0·5 mm. long, and this by the very short ejaculatory duct (13 µ), and finally by the fairly long cirrus, which is beset with very fine spines except at either extremity. The ovary and shell gland are situated at about the middle of the body with the testes behind them, and the uterus in front. The vitellaria extend from the ventral sucker to the posterior border. The eggs measure 120 µ to 130 µ in length and 77 µ to 80 µ in breadth, and resemble those of Echinochasma sp. in dogs. The larval stages are said to occur in shrimps.

Habitat.--Intestine of pig and man.

Distribution.--In man: India, Siam, China, Assam, Sumatra. It is common in Cochin China (16 out of 133 Annamites, Noc.), in Tonkin very rare. Dr. J. Bell has sent me [J. W. W. S.] human specimens from Hong Kong. In pigs: very common in South China (Heanly). Common in pigs in Hong Kong. Sixteen out of 248 pigs (i.e., 6 per cent.) infected in Hanoi.

*Fasciolopsis rathouisi*, Ward, 1903.

Syn.: Distomum rathouisi, Poirier, 1887.

Fifteen to 19 mm. long by 8·5 to 10·5 mm. broad by about 3 mm. thick. Skin with spines (Leiper). Bluntly oval or elliptical with short cephalic cone which is absent in Fasciolopsis buski. Oral sucker subterminal, 0·25 to 0·29 mm. broad by 0·2 mm. in antero-posterior diameter. Distant from ventral sucker by about twice its diameter. Ventral sucker 1·32 to 1·38 mm. broad by 0·68 to 0·7 mm. in antero-posterior diameter. Œsophagus extremely short. Cirrus sac not conspicuous and straight as in Fasciolopsis buski, but is convoluted. Testes one behind the other (according to Poirier they lie beside one another), more compactly branched, broader and denser than in Fasciolopsis buski. Ovary on right side, small, coarsely branched. Uterus in broad, closely grouped coils, packed with ova anterior to ovary. Vitellarian acini more numerous and somewhat differently distributed. Eggs 150 µ by 80 µ, thin shelled. [H. B. Ward, who has examined this species, and from whose account the above is mainly taken, considers that it is a good species, although the differences between it and Fasciolopsis buski are slight, while Odhner, who examined the original species, is of the opposite opinion.--J. W. W. S.] The parasite appears to cause diarrhœa, wasting and occasionally jaundice.

Habitat.--Intestine of man.

Distribution.--China, common in some parts (Goddard).

*Fasciolopsis goddardi*, Ward, 1910.

Twenty-one to 22 mm. long, 9 mm. broad. Skin with spines (Leiper). Uterus very closely coiled, most striking character is the large size of the vitelline acini. Imperfectly known.

Distribution.--China (Shanghai).

*Fasciolopsis fülleborni*, Rodenwaldt, 1909.

The fully extended fluke is tongue-shaped, 50 by 14 mm.; two contracted specimens measured 40 by 15 mm. and 30 by 16 mm. respectively. Skin without spines, with according to Leiper cephalic cone not clearly defined. Oral sucker circular, 0·75 mm. in diameter, slightly larger than that of Fasciolopsis buski. Ventral sucker 2·6 mm. in diameter (that of Fasciolopsis buski 1·6 to 2 mm.). Length 2·9 mm. (as in Fasciolopsis rathouisi), the excess of length over breadth being due to the posterior elongated sac-like prolongation of the sucker. Prepharyngeal sphincter present. Pharynx 0·7 mm. in diameter. Œsophagus practically absent. Gut cæca similar to those of Fasciolopsis buski.

Testes--regularly branched, separated by an incurving of the cæca, the anterior occupying a smaller area than the posterior.

Ovary--very small, as in Fasciolopsis buski, on the right side.

Shell Gland--almond-shaped, 2·3 by 1·2 mm. In Fasciolopsis buski it is round and smaller, 1 to 1·5 mm. in diameter.

Vitellaria--similar in distribution to those of Fasciolopsis buski, but the acini are strikingly small.

Cirrus Sac--is the most characteristic feature of this species. It is a powerfully built, convoluted sac standing out clearly on the body. It is not a uniform, straight cylinder 0·25 to 0·33 mm. in diameter, as in Fasciolopsis buski, but even in fully extended flukes is typically convoluted. It is 1 mm. thick in the middle, but in other parts varies much from this. The posterior end of the cirrus sac is at two-thirds or more of the distance from ventral sucker to shell gland. In the case of Fasciolopsis buski the posterior end of the sac only extends half-way.

Seminal Vesicle--has a peculiar convoluted, saccular and angular course, but the cæcal appendage characteristic of the genus appears to be absent!

Excretory System.--The main stem gives off very regular transverse branches which are well seen posteriorly.

Eggs.--100 µ by 73 µ. Thin shelled.

Habitat.--Intestine. Mahommedan from Calcutta.

[It is evident that a re-examination of fresh material is required before the validity of all these species can be accepted.--J. W. W. S.]

Family. *Troglotremidæ*, Odhner, 1914.

Genus. *Paragonimus*, Braun, 1899.

Body egg-shaped or somewhat elongated, generally more broadly rounded in front than behind. Covered all over with spear-shaped spines arranged in groups. Gut cæca winding with dilatations or constrictions in parts. Ventral sucker in or in front of the middle of the body. Excretory bladder cylindrical, very long and broad, reaching in front to the bifurcation of the gut. The lateral excretory canals join the bladder only a little in front of the excretory pore. Genital pore median just behind the ventral sucker. Genital sinus duct-like. Cirrus sac absent. Male terminal organs very small. Ejaculatory duct present. Testes and ovary deeply lobed, the testes in or just behind the middle, the ovary somewhat laterally placed just behind the ventral sucker. Uterus forms a coil behind the ventral sucker. Eggs rather large, thin shelled, the ovarian cell still unsegmented on deposition. Receptaculum seminis, small.

Parasitic in the lungs of mammals, enclosed in cyst-like cavities, generally in pairs.

Type Species.--P. westermanii in the tiger.

*Paragonimus ringeri*, Cobb., 1880.

Syn.: Distoma ringeri, Cobb., 1880; Distoma pulmonale, Baelz, 1883; Distoma pulmonis, Suga, 1883.

The body is of a faint reddish-brown colour and plump oval shape. The ventral surface a little flattened; 7·5 to 12 mm. in length, 4 to 6 mm. in breadth, and 3·5 to 5 mm. thick (in man). The oral sucker (0·75 mm.) is subterminal; the ventral sucker (0·8 mm.) somewhat in front of the middle of the body. Pharynx spherical, 0·3 mm. in diameter, or 0·4 by 0·3 mm.; œsophagus, 0·02 mm.; intestinal cæca convoluted, asymmetrical, the first part having the same structure as the œsophagus. The cuticle is covered with spines in groups; the excretory pore opens at the posterior end rather on the ventral surface, the excretory ducts open into the elongated bladder at the hind end near the pore. Genital pore behind the ventral sucker and median. Genital sinus 0·2 mm. long with thick wall, ejaculatory duct 0·13 mm., pars prostatica 0·2 mm., seminal vesicle duct-like of irregular outline. Behind the sucker the ovary on the left, and the closely packed uterine coil on the right (though amphitypy of these two organs is common); the two irregularly lobed testes lie side by side posteriorly. Vitellaria extensive, leaving only a median dorsal and ventral space free. Seminal receptacle probably absent; Laurer’s canal present. The eggs are oval, brownish-yellow, fairly thin shelled, and measure on an average 81·2 µ by 49·2 µ.

The following species are also known:--P. westermanii, Kerb., 1878, in the tiger, and P. kellicotti, Ward, 1908, in the pig, dog, and cat (N. America). Ward and Hirsch give the following differences between the spines of the three forms:--

P. ringeri. P. westermanii. P. kellicotti. Shape Chisel-shaped, Lancet-shaped, Chisel-shaped, moderately heavy. very slender. heavy. Distribution Circular rows, in Circular rows, Circular rows, groups. in groups. singly.

Two other species, P. rudis, Diesing, 1850, in a Brazilian otter (Lutra brasiliensis) and P. compactus, Cobbold, 1859, in the Indian ichneumon, are but little known.

Habitat.--Lungs, pleuræ, and especially the bronchi of man and dog. The alleged occurrence (of eggs) in other organs may be due to confusion with those of Schistosoma japonicum.

Distribution.--China, Korea, and especially in Japan, where, according to Katsurada, there are no districts that are entirely free from pulmonary flukes. The mountainous provinces of Okayama, Kumamoto, Nagano and Tokushima are the principal centres.

Pathology.--The number present in the lung varies from two to twenty, about. Usually one cyst contains one worm, but in the dog each cyst contains two. The cysts admit the tip of the finger, and have a fibrous wall 1 mm. thick. They originate partly from dilatation of bronchi and bronchioles. Others arise from the inflammatory reaction of lung tissue into which the worms have wandered. The worms and their eggs cause bronchitis and peribronchitis, catarrhal, hæmorrhagic, or purulent, and areas of consolidation. Areas containing eggs in their centre resembling tubercle nodules are not uncommon, and extensive cirrhosis of the lung may be found. As a result of these changes, emphysema and bronchiectasis also occur.

As to the development, only the following details are known: that the eggs, which before segmentation of the ovum reach the open in the sputum and through being swallowed also in the fæces, develop in water into a miracidium ciliated all over, which hatches and swims about freely. According to Manson this takes place in four to six weeks.

Sub-family. *Opisthorchiinæ*, Looss, 1899.

Genus. *Opisthorchis*, R. Blanch., 1845.

Opisthorchiinæ with lobed testes. Laurer’s canal present. Parasitic in the bile-ducts of mammals and birds.

*Opisthorchis felineus*, Riv., 1885.

Syn.: Distoma conus, Gurlt, 1831 (nec Creplin, 1825); Distoma lanceolatum, v. Sieb., 1836, v. Tright, 1889 (nec Mehlis, 1825 = Fasciolo lanceolata, Rud., 1803); Distoma sibiricum, Winogr., 1892; Distoma tenuicolle, Mühl., 1896.

This parasite is yellowish-red in the fresh condition, and almost transparent. The body is flat, with a conical neck at the level of the ventral sucker marked by a shallow constriction; this, however, is only noticeable in fresh and somewhat contracted specimens. Posteriorly to the ventral sucker the lateral borders run fairly parallel; the posterior end is either pointed or rounded off. The length and breadth vary according to the contraction, being usually 8 to 11 mm. by 1·5 to 2 mm. The suckers are about one-fifth to one-sixth of the length of the body distant from each other, and of about equal size (0·23 to 0·25 mm.). The œsophagus is hardly any longer than the pharynx, which lies close behind the oral sucker; the intestinal cæca reach almost to the posterior border and are often filled with blood. The excretory pore is at the posterior extremity, and the excretory bladder forks in front of the anterior testis. The testes in the posterior fourth of the body lie obliquely one behind the other; the anterior one has four lobes, the posterior one five lobes; the ovary is in the median line transversely, simple or slightly lobed; behind it lies the large pear- or retort-shaped receptaculum seminis and Laurer’s canal. The uterus is in the median field. The vitellaria occupy the fairly broad lateral areas, in about the central third of the body, beginning behind the ventral sucker and terminating at about the level of the ovary; the acini are small and arranged in groups of seven to eight, separated by interstices. The genital pore is close in front of the ventral sucker. The eggs are oval with sharply defined operculum at the pointed pole, 30 µ, by 11 µ.

This species, which is frequently confused with others, inhabits the gall-bladder and bile-ducts of the domestic cat especially; but is also found in the dog, in the fox, and in the glutton (Gulo borealis). It has been observed in France, Holland, North Germany (being particularly frequent in East Prussia), in Russia, Scandinavia, Siberia, Japan, Tonkin, Hungary, and Italy. The North American form (from cats and Canis latrans) is a distinct species (Opisthorchis pseudofelineus).

In man this species was first found by Winogradoff in Tomsk (nine cases), then by Kholodkowsky in a peasant from the neighbourhood of Petrograd who had travelled a great deal in Siberia, and finally by Askanazy in five persons who were natives of the East Prussian district of Heydekrug. In Tomsk, Opisthorchis felineus is the most frequent parasite of man that comes under observation at post mortem (6·45 per cent.), whereas Tænia saginata has only been found in 3·2 per cent., Echinococcus in 2·4 per cent., Ascaris lumbricoides in 1·6 per cent., and Oxyuris vermicularis in 0·8 per cent. of the autopsies. In the district of Heydekrug, however, the species in question is also frequent, as in a few years five cases came to our knowledge (of which three were diagnosed by the discovery of the eggs in the fæces).

In none of Winogradoff’s nine cases had the death of the patient been caused direct by the parasites, yet more or less extensive changes in the liver were found in all of them; such as dilatation of the bile-ducts with inflammation and thickening of their walls, and foci of inflammation or atrophy in the liver substance; icterus was present five times and atrophy of the liver an equal number of times; ascites was observed three times, and in two cases, probably of recent date, the organ was enlarged. The number of parasites found fluctuated between a few and several hundreds.

In two of Askanazy’s cases, which he examined more closely, carcinoma which had developed at the places most invaded by flukes was found at the post-mortem, so that perhaps there may be grounds for the connection which the author seeks to establish between cancer of the liver and the changes induced by the parasites; these changes consist of numerous and even ramified proliferations of the epithelium of the biliary duct into the connective tissue, which is likewise proliferated. The number of worms found in one case amounted to over 100; in a second case, in which the parasites had also invaded the pancreatic duct, their number was even larger.

Winogradoff as well as Askanazy found isolated flukes in the intestine also.

Unfortunately, nothing much is known of the history of the development of Opisthorchis felineus; we only know that when deposited the eggs already contain a ciliated miracidium, which, however, according to my experience, does not hatch out in water, but only after the entry of the eggs into the intestine of young Limnæus stagnalis; no further development, however, occurs. Winogradoff states that he has seen the miracidia hatch after the eggs had been kept in water for a month at 37° C.; and has even observed free miracidia in the bile of man and of a dog respectively. Although the whole post-embryonal development of the cat fluke remains yet to be investigated, Askanazy by a series of experiments on cats and dogs has discovered the mode of infection. The intermediate hosts are fish, and mainly the ide, in this country called Tapar (Idus melanotus, H. and Kr.), and of subsidiary importance the roach (Leuciscus rutilus). Both species of fish as well as others are readily eaten raw by man on the Courland lagoon (Baltic). It is, moreover, significant that those persons whom Askanazy found infected with the cat fluke were also infected with Dibothriocephalus latus, the intermediate host of which is also fish (Lota sp., Esox sp., Perca sp.).

In one of his nine cases Winogradoff also saw a small fluke covered all over with spines, which he conjectured to be the young stage of Opisthorchis felineus; as, however, according to my experience, this species, even in smaller specimens, is always without spines, the above hypothesis cannot be accepted. It is much more probable that one of the other species that also invade the liver of cats may accidentally be introduced into man; we know, in fact, that Metorchis albidus, Braun, and Metorchis truncatus, Rud., are both covered with spines. As, however, the spines of the first-named species are rather apt to fall off, and also as it possesses a different shape (spatula-shaped), it may be assumed that probably Winogradoff had found Metorchis truncatus, Rud., 1819, in his patient.

Genus. *Paropisthorchis*, Stephens, 1912.

Structure as in Opisthorchis, except that the ventral sucker and genital pore occur on the apex of a process or pedicle projecting from the anterior portion of the body. This process is about 1/2 mm. long, and is retractile.

*Paropisthorchis caninus*, Barker, 1912.

Syn.: Distoma conjunctum, Lewis and Cunningham, 1872; Opisthorchis noverca, M. Braun, 1903 (pro parte); Opisthorchis caninus, Barker, 1912 (?).

Length varies from 2·75 to 5·75 mm. in preserved specimens, average 3·6 to 5·2 mm. Body uniformly spinose, though as a rule spines are not present on the pedicle. Body slightly concavo-convex, the concavity being ventral. Oral sucker 0·28 mm. Pharynx 0·224 by 0·184 mm. Œsophagus 0·04 mm. Ventral sucker 0·176 mm. in diameter. Pedicle about 1/2 mm. long, may be completely retracted.

Genital Pore--opens on the apex of the pedicle in front of the ventral sucker. Its exact position varies with the state of contraction of the parts. In certain cases it actually opens within the cuticular border of the sucker, in other cases it opens externally to the sucker and anterior to it. The opening is covered with scales. The vas deferens and uterus run alongside one another until they merge near the apex of the pedicle into a common sinus.

Vitellaria--consist of eight acini on each side, extending from slightly behind the base of the pedicle to the anterior border of the ovary, or as far back as a line separating the posterior border of the ovary from the anterior border of the anterior testis.

Testes.--Anterior testis 0·496 by 0·44 mm.; posterior testis 0·52 by 0·48 mm., usually ovoid, though both may be regularly lobed. The anterior testis is usually on the left side.

Ovary--multilobular, the lobes 6 to 8 being irregular in size and shape.

Shell Gland--extensive and diffuse, occupying an area which approximately corresponds with the loop of the transverse vitelline ducts.

Seminal Receptacle--globular, to the right of and dorsal to the posterior lobe of the ovary.

Laurer’s Canal--generally runs from the end of the receptacle with a single curve medially and backwards.

Uterine Coils--form loosely packed transverse coils terminating slightly in front of the level of the first vitelline acini. From here the uterus passes forwards into the pedicle to the left and ventral to the seminal vesicle.

Seminal Vesicle--commences about the level of the first vitelline acini. The coils displace the uterus ventrally and to the left. In the pedicle the vesicle diminishes in extent and lies in its dorsal (anterior) side.

Habitat.--Liver of pariah dogs, India. In North-Western Provinces about 40 per cent. are infected. This fluke appears to be different from Amphimerus (Opisthorchis) noverca in man, as the latter has not the pedicle on the summit of which lie the sucker and common genital pore.

Genus. *Amphimerus*, Barker, 1912 (?).

Structure as in Opisthorchis, except that the vitellaria are separated into two portions, an ant-ovarial and a post-ovarial.

*Amphimerus noverca*, Barker, 1912 (?).

Syn.: Distomum conjunctum, McConnell, 1876 (nec Cobbold, 1859); Opisthorchis noverca, M. Braun, 1903 pro parte.

At the autopsy of two Mahommedans who died in Calcutta, McConnell found a large number of Distomata in the thickened and dilated bile-ducts. The worms were lancet-shaped, covered with spines, and measured 9·5 to 12·7 mm. in length and 2·5 mm. in breadth. The two suckers lie very close to one another, the anterior one being larger than the ventral; the genital pore opens immediately in front of the ventral sucker; pharynx spherical; intestinal cæca extending far back. At the commencement of the posterior third of the body the two testes, somewhat apart, the anterior one roundish, the posterior one distinctly lobed. The transverse and slightly lobed ovary in front of the bifurcation of the *Y*-shaped excretory bladder, whence the uterus, in convolutions barely spreading beyond the central field, extends to the pore; the vitellaria in the lateral areas commence behind the ventral sucker and extend to the testes. Cirrus pouch absent. Eggs oval, 34 µ by 21 µ.

Genus. *Clonorchis*, Looss, 1907.

Structure as in Opisthorchis, distinguished, however, by the branched testes situated one behind the other, the branches of which ventrally encroach upon the gut forks; dorsal to the testes the *S*-shaped excretory bladder, the main branches of which, arising at the level of the bifurcation of the gut, open into the bladder below its anterior end. Parasitic in the bile-ducts of mammals and man.

[272] This species from Canis fulvus was for long thought to be the same as that here described as Amphimerus noverca. It probably does not belong to the genus Metorchis.

*Clonorchis sinensis*, Cobbold, 1875.

Syn.: Distoma sinense, Cobbold, 1875; Distoma spathulatum, R. Leuckart, 1876 (nec Rudolphi, 1819); Distoma hepatis innocuum, Baelz, 1883.

In shape resembles Opisthorchis felineus, 13 to 19 mm. long, 3 to 4 mm. broad, at the beginning of sexual maturity 12 to 13 mm. long, 2·5 to 3 mm. broad. Oral sticker 0·58 to 0·62 mm., ventral sucker 0·45 to 0·49 mm. in transverse diameter. In the parenchyma numerous yellowish or brownish granules, especially behind the oral sucker and at the posterior end. Testicular branches very long, in the anterior testis often four, in the posterior testis five branches. Ovary generally with three large lobes and a smaller lobe. Vitellaria not always symmetrical, generally extending laterally from the ventral sucker to the ovary, interrupted in parts.

Eggs 26 µ to 30 µ by 15 µ to 17 µ. Average 29 µ by 16 µ.

This (?) species was discovered in 1874 by McConnell, in Calcutta, in the bile-ducts of a Chinaman who died shortly after being admitted into hospital.

Habitat.--Bile-ducts of man, dog and cat.

Distribution.--Especially in China, apparently rare in Japan.

*Clonorchis endemicus*, Baelz, 1883.

Syn.: Distoma sinense s. spathulatum p.p.; Distoma hepatis endemicum s. perniciosum, Baelz, 1883; Distoma japonicum, R. Blanchard, 1886.

Very similar to the previous species and consequently generally confused with it. Length between 6 and 13 mm., width varying between 1·8 and 2·6 mm. Oral sucker 0·37 to 0·5 mm., usually 0·43 to 0·45 mm. in transverse diameter; ventral sucker 0·33 to 0·45 mm., usually 0·37 to 0·40 mm. No pigment in parenchyma; anterior testis with four, posterior testis with five branches. Vitellaria continuous, ova 26 µ by 13 µ to 16 µ.

Habitat.--Bile-ducts of man, dog, cat and pig.

Distribution.--This species occurs very frequently in man, in certain districts of Japan, especially in the province of Okayama, Central Japan, in particular localities of which above 60 per cent. of the population are infected. The worms are sometimes found in enormous numbers in the liver (upwards of 4,000), also in the pancreas and rarely in the duodenum. It is common in Tonkin and Indo-China. Léger in Tonkin found 50 per cent. of people apparently in normal health infected, so that probably symptoms only arise when the infection is intense. [The exact distribution of these two species is, however, not precisely defined at present, as commonly no distinction is made between them.--J. W. W. S.]

Verdun and Bruyant deny, in opposition to Looss, the possibility of being able to distinguish within the genus Clonorchis the two species described, but they admit the justification for the new genus. They also report the occurrence of Opisthorchis felineus in man in Tonkin (Compt. Rend. Soc. de Biol., lxii, 1907).

Pathology.--Both species of Clonorchis give rise to grave symptoms. The liver is generally enlarged, though when the infection has lasted some time it begins to contract. The surface of the organ is studded with white vesicles, and on cutting into it one sees numerous cavities with thickened walls (distended bile-ducts) filled with a brownish fluid containing innumerable eggs, which cause its colour. Microscopically, the epithelium of the bile-ducts is either (1) entirely destroyed, or (2) actively proliferates, forming an adenomatous outgrowth. Occasionally this proliferation is not limited by the wall of the bile-duct but penetrates it and leads to a growth of numerous new ducts, forming a malignant biliary adenoma. The bile-ducts have their connective tissue wall greatly sclerosed. These fuse with one another, forming areas of sclerosis devoid of liver tissue. As a result of these changes the liver cells atrophy and undergo fatty pigmentary and granular degeneration. Besides these changes, due probably to the toxic action of the flukes, mechanical obstruction due to the actual plugging of the ducts by the flukes causes retention of bile and icterus, and through pressure on veins, ascites and hypertrophy of the spleen.

To what extent blood or bile respectively forms the food of the flukes is uncertain.

Life-history.--(Kobayashi, 1911, Mitteilungen aus dem kaiserlichen Institut für Infektions-Krankheiten zu Tokio, pp. 58–62.)

It results from the work of Kobayashi in Japan that fresh-water fish form the second intermediate host for Clonorchis endemicus. He fed cats with encysted flukes (cercariæ) from various fish and easily succeeded in infecting them, e.g. a kitten, proved to be uninfected by repeated examination of its fæces, was fed on infected fish; a month later innumerable flukes were found in the bile-ducts, gall-bladder, pancreas and even in the duodenum. The fish infected were Leucogobis güntheri, Pseudorasbora parva, and to a less extent Acheclognathus lanceolata, Acheclognathus limbata, Paracheclognathus rhombea, Pseudoperilampus typus, Abbottina psegma, Biwia zezera and Sarcocheilichthys variegatus. The cysts occur throughout the muscles and subcutaneous tissue of the fish. Length 0·13 mm., breadth 0·1 mm. The cercaria lies folded in the cyst, length 0·5 mm. breadth 0·1 mm. It tapers posteriorly. Skin at first covered with fine spines, disappearing as they grow older. Body dotted with fine pigment.

The first intermediate host is still unknown.

Sub-family. *Metorchiinæ*, Lühe, 1909.

Genus. *Metorchis*, Looss, 1899, emend. auctor.

Hind end rounded. Gut forks reach extreme end. Testes only slightly lobed, filling the hind end.

*Metorchis truncatus*, Rud., 1819.

This species, which attains a length of 2 mm., is slender and conical, the anterior end is pointed and the posterior truncated, and provided with a muscular tuberosity that resembles a terminal sucker; for this reason the discoverer of the species (Rudolphi) classed it with the Amphistomes. The cuticle in the young, as well as in the adult specimens, is entirely and closely covered with spines. Suckers about equal in size (0·134 to 0·172 mm.); the ventral sticker lies somewhat in front of the middle of the body. The pharynx is small (0·09 mm.), the œsophagus minute, the intestinal cæca reach to the posterior extremity. Between them, and in front of their blind ends, lie the two elliptical testes, one generally a little in front of the other. In front of them, either in the median line or somewhat laterally, the spheroidal ovary is situated; in front, again, is the uterus, the coils of which usually extend beyond the median field. The vitellaria are at the sides of the central third of the body, thus commencing in front of the ventral sucker; cirrus pouch absent; the genital pore is close in front of the acetabulum. The excretory pore is terminal (?). Eggs 29 µ by 11 µ.

Metorchis truncatus lives in the bile-ducts of the seal, cat, dog, fox, and glutton (Gulo borealis). The source of infection is unknown, although one would suspect fish. Askanazy did not succeed in getting this fluke in his feeding experiments, but another species, Metorchis albidus, not uncommon in cats by feeding them on roach (Leuciscus rutilus).

Family. *Heterophyiidæ*, Odhner, 1914.

Genus. *Heterophyes*, Cobbold, 1866.

Syn.: Cotylogonimus, Lühe, 1899; Cænogonimus, Looss, 1899.

No crown of spines on head. Body divided into a narrow, movable, anterior part (neck), and a broader, less movable, posterior portion, which contains the genitalia. The suckers separated from one another by a space equal to half the length of the body or more; the pharynx is close behind the oral sucker; the œsophagus is long; the intestinal cæca extend to the posterior border; the genital pore is placed laterally, and behind the ventral sucker. Genital sucker provided with a circlet of chitinous rodlets, shaped like stags’ horns. The testes are at the posterior end, the ovary in a median position in front of them. Laurer’s canal with receptaculum seminis present; the small vitellaria are at the sides of the posterior part of the body. Parasitic in the intestine of mammals and birds.

*Heterophyes heterophyes*, v. Sieb., 1852.

Syn.: Distomum heterophyes, v. Siebold, 1852; Heterophyes ægyptica, Cobbold, 1866; Mesogonimus heterophyes, Railliet, 1890; Cœnogonimus heterophyes, Looss 1900; Cotylogonimus heterophyes, Braun, 1901.

Length up to 2 mm., breadth 0·4 mm.; the neck not sharply defined; in life it stretches to double the length of the hind body. The scales are rectangular, 5 µ to 6 µ by 4 µ, their posterior margin serrate with seven to nine teeth. Cuticular glands are numerous on the ventral surface, especially in the fore part of the body, and partly discharge at the anterior border of the oral sucker. The oral sucker is 0·09 mm., the ventral sucker 0·23 mm. in diameter; the pharynx measures 0·05 to 0·07 mm. in length; the œsophagus is about three times as long; posteriorly the intestinal cæca are directed one towards the other and terminate beside the excretory bladder. Close in front of the posterior ends of the intestinal branches are the two elliptical testes, which are not exactly on the same level. In the middle in front of them is the receptaculum seminis, and in front of the latter lies the spherical or elliptical ovary. The two vasa efferentia unite to form the vas deferens, which after a short course passes over into the angularly bent seminal vesicle; after the entry of the prostatic glands it becomes united with the metraterm (vagina), and the common duct opens into the genital sucker. The latter is somewhat smaller than the ventral sucker, lateral to and close (0·15 mm.) behind it, and bears a not entirely closed ring of from seventy-five to eighty chitinous rods (20 µ in length). The vitellaria on either side consist of about fourteen acini. The uterus is spread almost throughout the entire posterior part of the body. The eggs have thick shells with a knob resembling that of Clonorchis eggs but not so prominent, and measure 30 µ by 17 µ; they contain a completely ciliated miracidium with a rudimentary intestinal sac.

This species was discovered in 1851 by Bilharz in the intestine of a boy who died in Cairo; a second case was only found in 1891 and published by R. Blanchard, so that it appeared as if the species were very scarce. According to Looss, this is, however, not the case, but the species easily escapes notice on account of its small size. Looss found it in Alexandria twice in nine autopsies, and once in Cairo, and has recently stated that in man “it is not at all uncommon to meet with the parasite in cadavers, and the eggs of the worm in the stools of the patients.” Leiper records one case from Japan and one from China. The parasites occupy the middle third of the small intestine, and even when present in large numbers appear to be harmless.

This small species, according to Looss, frequently occurs in Egyptian dogs, less so in cats, and has also been found in the fox, as well as once in Milvus parasiticus; Janson also reports this species from the intestine of the dog in Japan.

*Metagonimus*, Katsurada, 1913; Yokogawa, Leiper, 1913.

Resembles in general structure Heterophyes. In the arrangement of its ventral genital suckers resembles but differs from that of Tocotrema,[273] Looss. The ventral and genital suckers lie laterally and on the right.

[273] In the genus Tocotrema the common genital duct opens into the ventral sucker.

*Metagonimus yokogawai.* Katsurada, 1913.

Syn.: Yokogawa yokogawai, Leiper, 1913.

One to 1·5 mm. long, seldom 2·5 mm., and 0·4 to 0·7 mm. broad; elliptical in shape. The body is thickly covered with nail-shaped spines about 10 µ long. Oral sucker 77 µ, to 85 µ in diameter. Ventral sucker characteristic and peculiar 0·12 to 0·14 mm. by 0·08 to 1 mm. It is a sac-like organ placed deeply in the body, but does not open as in other flukes on the ventral surface. Testes elliptical, not quite symmetrically placed at the hind end of the body. Vesicula seminalis retort-shaped, situated transversely, internal to the ventral sucker. Pars prostatica present. Ejaculatory duct opens with the uterus into a genital sinus, which, together with the internal opening of the ventral sucker, opens into a pit at the front of the ventral sucker. The opening of the genital sinus and that of the ventral sucker are furnished with a complex muscular apparatus. Ovary spherical, 0·12 to 0·13 mm. in diameter, lies in the middle of the hind body. Receptaculum seminis and Laurer’s canal present. Vitellaria in the hind half of the body, consisting of about ten acini on each side. Shell gland to the left of the ovary. Uterus forms three to four transverse coils. Eggs elliptical, double contoured, yellowish-brown in colour. There is no shoulder below the operculum as in the eggs of Cl. sinensis. At the rounder end there is a thickening or knob different from the spine-like or hook-like process seen in Cl. sinensis. Dimensions 28 µ by 16 µ.

Habitat.--Mainly in upper or middle portion of jejunum, rarely in cæcum. They penetrate deep into the mucosa, but not into the submucosa, and post mortem appear as a number of small brown points. They frequently occur in the solitary glands, which they destroy. They cause chronic catarrh of the gut. Parasitic in man and mammals.

Geographical Distribution.--Japan.

Life-history.--The cercarial stage occurs in a trout (Plecoglossus altivelis) and seldom in Crassius sp. and Cyprinus sp. Infection takes place through the eating of the fish raw. Seven to sixteen days later eggs appear in the fæces (of dog).

Family. *Dicrocœliidæ*, Odhner, 1910.

Genus. *Dicrocœlium*, Dujardin.

Dicrocœliidæ, with leaf-shaped bodies, pointed posteriorly and anteriorly. Greatest width behind the mid-line. Vitellaria double. The testes smooth or indented, lying symmetrically or obliquely beside or behind the ventral sucker. The ovary approaches the median line behind one testis. Parasitic in the liver and gall-bladder (rarely in the intestine) of members of all classes of vertebrate animals--by preference in birds and mammals.

*Dicrocœlium dendriticum*, Rud., 1819.

Syn.: Dicrocœlium lanceatum, Stil. and Hass., 1896; Fasciola lanceolata, Rud., 1803 (nec Schrank, 1790); Distomum lanceolatum, Mehlis, 1825; Dicrocœlium lanceolatum, Dujardin, 1845.

Body lancet-shaped, narrowing especially at the anterior extremity; length 8 to 10 mm., breadth 1·5 to 2·5 mm., the greatest breadth usually behind the middle of the body. Suckers distant from each other by about one-fifth the length of the body; oral sucker about 0·5 mm., ventral sucker about 0·6 mm. Pharynx globular, adjoining the oral sucker; œsophagus 0·6 mm. in length; intestinal cæca reach to four-fifths of the body length. Genital pore at the level of the bifurcation of the intestine; cirrus pouch small and slender. The large, slightly lobed testes lie obliquely one behind the other behind the ventral sucker; the ovary, which is considerably smaller, is placed behind the posterior one; the vitellaria, commencing at the level of the posterior testis, terminate far before the cæca. The uterus, situated behind the ovary, extends throughout the posterior end, not confined to the central field, but overlapping the lateral fields with its transverse coils; at the posterior edge of the body it turns back again and winds forwards to the ovary in transverse loops, then between the testes, and finally, dorsal to the ventral sucker, terminates in the genital pore. The thick-shelled eggs when young are yellowish, when older dark brown. They measure 38 µ to 45 µ by 22 µ to 30 µ. They contain an oval or roundish miracidium, only the anterior part of which is ciliated, and which possesses a rudimentary intestinal sac with a boring spine. The miracidia do not hatch out in water spontaneously, but, according to Leuckart, in the intestines of slugs (Limax, Avion), but they do not develop either in these (slugs) or in water-snails.

The lancet fluke inhabits the biliary duct of herbivorous and omnivorous mammals (sheep, ox, goat, ass, horse, deer, hare, rabbit, pig), and is often found associated with the liver fluke; it is not, however, so common nor so widely disseminated, nevertheless, it has been met with outside of Europe, namely, in Algeria, Egypt, Siberia, Turkestan, and North and South America.

In man it is still more uncommon than the liver fluke, and has hitherto only been observed seven times (Germany, Bohemia, Italy, France, and Egypt); it may, however, have occurred more frequently, and have been overlooked, as in slight infections it produces no special symptoms.

The intermediate host is still unknown. Leuckart for some time held the opinion that small species of Planorbis from fresh water, which contain encysted Distomata, were to blame, and he supported his views by a feeding experiment which seemingly yielded positive results; this, however, is not definitely proved. Piana’s statement that small land snails are the intermediate hosts has also not been proved.

Family. *Echinostomidæ*, Looss, 1902.

Sub-family. *Echinostominæ*, Looss, 1899.

Genus. *Echinostoma*, Rud. 1809; Dietz, 1910.

Fore-body not bulging. Greatest width at or behind the ventral sucker. Oral sucker not atrophied. Collar kidney-shaped with a double dorsally unbroken row of spines, terminating in four to five angle spines. The border spines of the aboral series not larger than the oral. Skin spined or smooth. Body elongated. Uterus long with numerous transverse coils. Ventral sucker in the anterior quarter of body. Cirrus sac small, almost completely in front of the ventral sucker. Testes round or oval, smooth incurved or lobed, in the hinder half of body. Ovary median or lateral in front of testes. Vitellaria from hinder margin of ventral sucker to end of body. Eggs oval, 84 µ to 126 µ by 48 µ to 82 µ.

The spines placed most ventrally, or those placed most medially on ventral surface, are from differences of position or form termed “angle” spines, the rest “border” spines.

Type.--Echinostoma echinatum, Rud.

*Echinostoma ilocanum*, Garrison, 1908.

Length 4 to 5 mm., breadth 1 to 1·35 mm., thickness 0·5 to 0·6 mm. The circum-oral disc 0·3 mm. broad, separated by a shallow groove from the body. Crown of forty-nine spines and five to six angle spines on each side continuous with an irregularly alternating series of fourteen spines on the dorsum. Largest spines are 34 µ long, 8 µ thick at the base. The remainder of the dorsal spines are 24 µ by 6 µ. Skin thickly covered with scales on the margins of the body as far back as the level of the hind testis. Oral sucker, 0·18 mm.; ventral sucker, 0·4 to 0·46 mm. Its anterior border about 0·07 mm. from the anterior end. Pharynx 0·17 mm. long, 0·11 mm. broad. Testes about mid-line of the body, much lobed; the lobes of the anterior testis run transversely, while the axis of the posterior testis is longitudinal, as often occurs in the Echinostomidæ. Cirrus sac reaches to the centre of the ventral sucker. Ovary transversely oval in front of the testes. Vitellaria commence about half-way between the ventral sucker and ovary and extend to the posterior end. Eggs numerous, 92 µ to 114 µ by 53 µ to 82 µ.

Average.--99·5 µ by 56 µ.

Habitat.--Gut of man (Filipinos), Philippine Islands.

*Echinostoma malayanum*, Leiper, 1911.

Twelve millimetres long, 3 mm. broad, 1·3 mm. thick. Ends bluntly rounded. At the anterior end a ventral furrow on either side, one-third the width of the body, marking off the circum-oral collar. Along its edge is a row of forty-three spines extending across the middle line dorsally but not ventrally. The spines vary in size from 0·07 mm. in length (ventrally) to 0·05 to 0·016 mm. (dorsally). Cuticular spines also exist on the ventral side as far back as posterior end of body, but dorsally limited to a triangular area ending in front of the ventral sucker. Oral sucker 0·07 mm. thick, occupying the middle third of the circum-oral disc; pharynx 0·25 mm. in diameter; œsophagus 0·04 mm. long; gut cæca simple, extending to end of body; ventral sucker 0·9 mm. long by 0·75 mm. broad by 0·7 mm. deep; wall about 0·25 mm. thick. The sucker is inclined at an angle of 40° to the ventral surface. Testes lobed, one behind the other, behind the ventral sucker. Cirrus pouch well developed, reaching to the posterior edge of the sucker. Genital pore in the angle between neck and anterior lip of ventral sucker. Ovary smooth, 0·3 mm. in diameter, 0·85 mm. behind ventral sucker. Vitellaria very numerous, extending from posterior margin of sucker to posterior end of body, where they intermingle. Eggs few in number, brown and large.

Habitat.--Gut of man (Tamils), Malay States.

Sub-family. *Himasthlinæ*, Odhner, 1910.

Genus. *Artyfechinostomum*, Clayton-Lane, 1915.

Crown of thirty-nine spines, continuous over dorsum. Two corner spines long. Vitellaria extend from posterior margin of sucker to posterior end of fluke. Eggs without filament. [Although the possession of strong rose-thorn hooks is given by Odhner as a sub-family characteristic, yet in this genus assigned to this sub-family they have not been seen.--J. W. W. S.]

*Artyfechinostomum sufrartyfex*, Clayton-Lane, 1915.

Spirit specimens: 9 by 2·5 by 0·8 mm. thick. Ventral sucker conspicuous, 1 mm. in diameter. Cirrus sac 2 mm. long. Testes lobed, about 1·5 mm. in diameter. Posterior border of posterior testes 1 mm. from posterior end. Vitellaria meet posteriorly behind the posterior testis.

Family. *Schistosomidæ*, Looss, 1899.

Genus. *Schistosoma*, Weinl, 1858.

Syn.: Gynæcophorus, Dies., 1858; Bilharzia, Cobb., 1859; Thecosoma, Moq. Tandon, 1860.

The males have bodies that widen out considerably behind the ventral sucker, the lateral parts of which in-roll ventrally, forming the almost completely closed canalis gynæcophorus, within which the female is enclosed. There is no cirrus pouch. The male has five or six testes, the females are filiform; the uterus is long. There is no Laurer’s canal. The ova almost equally attenuated at either extremity; they have a small terminal spine, and are not provided with a lid. They contain a miracidium, ciliated on all sides, which is characterized by the possession of two large glandular cells, which discharge anteriorly beside the gastric sac. They live in the vascular system of mammals. (An allied genus [Bilharziella] lives in the blood-vessels of birds.)

*Schistosoma hæmatobium*, Bilharz, 1852.

Syn.: Distoma hæmatobium, Bilh.; Distoma capense, Harley, 1864.

The Male is whitish, 12 to 14 mm. in length, but is already mature when 4 mm. long. The anterior end is 0·6 mm. or a little over in length. The suckers are near each other, the oral sucker is infundibular, and the dorsal lip is longer than the ventral one. The ventral sucker is a little larger, 0·28 mm., and is pedunculated. A little behind the ventral sucker the body broadens to a width of 1 mm., decreasing, however, in thickness; the lateral edges in-roll ventrally, so that the posterior part of the body appears almost cylindrical, 0·4 to 0·5 mm. in diameter; the posterior extremity is somewhat more attenuated. The dorsal surface of the posterior part of the body is covered with spinous papillæ. There are delicate spines on the suckers, and larger ones invest the entire internal surface of the gynæcophoric canal, as well as a longitudinal zone at the edge of that side of the external surface that is covered by the other side rolling over it. The œsophagus is beset with numerous glandular cells (fig. 173), and presents two dilatations; the intestinal bifurcation is close in front of the ventral sucker, the two branches uniting sooner or later behind the testes into a median trunk, which may again divide at short intervals. The excretory pore is at the posterior end, but placed somewhat dorsally; the genital pore is at the beginning of the gynæcophoric canal, thus behind the ventral sucker; into it opens the vas deferens which, posteriorly, broadens into the seminal vesicle and then continues as the vasa efferentia of the four or five testes (fig. 173).

The Female--filiform, about 20 mm. in length, pointed at each end, and measuring 0·25 mm. in diameter in the middle. Their colour varies according to the condition of the contents of the intestine. (Posteriorly they are dark brown or blackish.) The cuticle is smooth except in the sucker, where there are very delicate spines, and at the posterior end, where there are other larger spines. The oral sucker is a little larger than the pedunculated ventral sucker (0·07 and 0·059 mm. respectively). The anterior part of the body, 0·2 to 0·3 mm. in length; the œsophagus is as in the male. The intestinal bifurcation is in front of the ventral sucker, the two branches uniting behind the ovary and the trunk running in a zigzag manner to the posterior border. There are indications of diverticula at the flexures. The ovary is median. In young females it is of an elongated oval shape; in older females the posterior end becomes club-shaped, whereas the anterior end becomes attenuated; the oviduct originates at the posterior end, but immediately turns forwards and joins the parallel vitelline duct in front of the ovary (fig. 174), where the shell gland cells open; the common canal becomes dilated to form the oötype, and then proceeds as the uterus, with only slight convolutions, along the central field to the genital pore, which lies in the middle line immediately behind the ventral sucker. The single vitellarium starts behind the ovary and extends to the posterior end. The acini are situated at the sides of the excretory duct, which runs a median course. The eggs are compact spindles, much dilated in the middle; they have no lid, and are provided with a terminal spine (rudimentary filament) at the posterior end, measuring 120 µ to 150 µ in length and 40 µ to 60 µ in breadth, but vary in size and shape (fig. 175).

Distribution.--In order to understand the distribution of the worms and eggs in the body, it may be well to recall the blood supply of the abdominal and pelvic organs. It is generally assumed that the early life (? cercarial stage) of the worms occurs in the liver, and that the young worms travel from here, where they are invariably found, to their various sites along the portal vein and its tributaries and so against the blood stream. The tributaries of the portal vein are:--

(1) Superior mesenteric, the tributaries of which are: (a) the veins of the small intestine; (b) ileo-colic; (c) right colic; (d) middle colic; (e) right gastro-epiploic; and (f) inferior pancreatic. By these paths infection of the small intestine, ascending and transverse colon and pancreas would occur.

(2) Splenic. (Ova have been recorded by Symmers in the spleen.)

(3) Inferior mesenteric, the tributaries of which are (a) superior hæmorrhoidal veins from the upper part of the hæmorrhoidal plexus; (b) sigmoid veins from sigmoid flexure and lower portion of descending colon; (c) left colic vein draining descending colon.

The superior hæmorrhoidal veins form a rich plexus in the rectum, and below this level in the upper and middle parts of the anal canal. The plexus forms two networks, an internal plexus in the submucosa and an external on the outer surface. The internal plexus opens at the anal orifice into: (a) branches of the inferior hæmorrhoidal vein (from the pudic); (b) the external plexus. The external plexus gives off: (a) inferior hæmorrhoidal opening into internal pudic (of internal iliac vein); (b) mid-hæmorrhoidal into internal iliac or its branches; and (c) superior hæmorrhoidal opening into inferior mesenteric. The external plexus further communicates with the vesico-prostatic plexus. The vesico-prostatic (vaginal) plexus opens into the vesical veins, which drain into the interior iliac vein. This plexus also receives afferents from the pudendal plexus, the chief tributary of which is the dorsal vein of the penis. The pudendal plexus also receives branches from the inferior pudic and the anterior surface of the bladder.

There is thus a communication between the portal vein and the vena cava by means of these plexuses, viz., through the inferior and middle hæmorrhoidals, and by the inferior hæmorrhoidals to the bladder and thence by the vesical veins or the pudic to the caval system (interior iliac).

It is thus by the inferior mesenteric and its tributaries that the worms reach the descending colon, rectum, anal canal, and eventually the bladder, and in some cases the caval system.

Before considering what is actually found post mortem in these veins and the organs drained by them, we may further recall the fact that the calibre of “medium” veins is 4 to 8 mm., “small” veins less than 40 µ in diameter and capillaries 8 µ to 20 µ. Further, the maximum diameter of the male worm is 1 mm., that of the female 280 µ and eggs in utero 80 µ to 90 µ long by 30 µ to 40 µ.

Liver and Portal Vein.--Here worms are most easily found post mortem. Often only males are found and these of the same size, and if females occur only a few worms are found in copulâ. The worms are frequently not full size and the males may contain no free spermatozoa in their testes, and as regards the females some may be fertilized, others not, as shown by the presence or absence of spermatozoa in the seminal receptacle or uterus. In either case they may contain eggs--lateral-spined--usually one, less often two, but there may be as many as five or six. These eggs may also show some abnormality, which takes the form of: (1) abnormal contents, viz., disintegrating yolk cells with or without an ovarian cell; (2) abnormal shape but with normal contents and probably represented by the collapsed and empty egg-shells which are found in the tissues.

As to the interpretation of these facts, Looss believes that these lateral-spined eggs are products of young females whose egg-laying is not at first properly regulated. The shape that the eggs take, viz., with a lateral spine, is determined by an excess of material--ovarian and yolk cells--being present in the oötype. The shape of eggs depends upon the position they have in the oötype during their formation. In young females an excess of cells--yolk cells especially--accumulates, distending not only the dorsal wall but a portion also of the short duct joining the oötype to the uterus. The result of this is that the axis of the oötype and egg is almost transverse to the body, and the posterior funnel-shaped portion of the oötype, instead of being terminal, has now a lateral or rather a ventral position, so that the spine which occupies this portion, instead of being terminal, is now lateral. It is noteworthy that these lateral-spined eggs are thicker, owing to the excess of material present, and not uncommonly have a curved anterior border, due to a projection of the anterior end into the anterior opening of the oötype.

As these eggs are being laid by females in the portal vein they are carried back to the liver by the blood stream. The liver is one of the commonest sites for these eggs; also terminal-spined eggs may be found here for the same reason.

Hæmorrhoidal Veins.--Mature worms, generally in copulâ, are usually found here, though young not fully grown females may also occur. The tissues of the rectal wall (or colon) show, as a rule, large quantities of lateral-spined eggs, though less often only terminal-spined eggs may be found.

Vesico-prostatic Plexus.--Worms in copulâ are found in the veins of the submucosa in the bladder, and the eggs in the mucosa, and those voided are usually terminal-spined, though lateral-spined eggs are not so rare as generally thought. The problem next arises as to how the eggs get to the lumen of the gut or bladder.

The female worm is 280 µ in diameter. Veins in the submucosa of the rectum less than 178 µ in diameter are not affected with endophlebitis. It is probable that the female even by stretching could not penetrate much beyond this. Eggs are probably then laid in the submucosa as near the muscularis mucosa as possible. Now if the eggs are laid in a vein of larger calibre than the worm fills, the eggs would be carried back to the inferior mesenteric vein, so that presumably the worm must succeed in blocking the vein already narrowed by endophlebitis, so that by the stasis which ensues the eggs may escape from the veins. How this occurs is not exactly known; it is not necessarily due to the spine, as the same escape into the tissues occurs in spineless eggs, such as those of Schistosoma japonicum. The eggs, then, pass as foreign bodies through the tissues. Another hypothesis is that the worms leave the veins in order to lay their eggs, but the evidence is against this.

Caval System.--Occasionally worms that have passed through the vesical plexus may be found in the iliac vein, inferior vena cava, and even the lungs. If the worms are young they contain a lateral-spined egg; if adult, numerous (50 to 100) terminal-spined eggs.

Lungs.--When the liver is strongly infected with (terminal-spined) eggs it is possible that by passive movements some may pass into the intralobular veins, and thence by the inferior vena cava to the lungs.

Gall-bladder.--Similarly terminal-spined eggs pass into the bile-capillaries and gall-bladder (where they may be abundant), and so into the fæces.

Detection of Eggs.--Occasionally eggs may be found in various other parts of the body. They are best detected by macerating pieces of the tissue in question in about 1/4 per cent. hydrochloric acid at 50 to 60°C. (Looss).

Pathological changes:--

Rectum.--These have been studied thoroughly by Letulle in the case of an apparently pure infection of the rectum.[274] They take the form of a chronic diffuse inflammation, which may result in--(1) ulceration, or (2) hyperplasia of the mucosa, producing adenomata.

[274] It is noteworthy that in this almost classical case no worms were found in any of the sections. It is further noteworthy that the eggs in the rectum showed great irregularity of form. Eggs with a spine at each end were not uncommon; exceptionally eggs with two polar spines and one lateral.

Ulcerative Form.--The mucosa is transformed into a mass of vascular connective tissue. The connective tissue spaces next become invaded by numerous mononuclear cells. The tissue itself undergoes diffuse sclerosis, becoming hard and fibroid. Eventually ulcerative necrosis sets in. During these changes the Lieberkühn glands are destroyed. The process does not extend to the submucosa, in this respect differing from that in chronic dysentery.

Hyperplastic Form.--The Lieberkühn glands of the mucosa at first hypertrophy; then there is an actual hyperplasia resulting in adenomata. The interstitial tissue of the glands is also greatly hypertrophied, giving rise to very vascular granulations. These growths are often hollow and contain worms. Many eggs are found in the mucosa on their way to the lumen of the gut.

The muscularis mucosa is thickened up to twice or even ten times the normal. Its vessels are dilated (36 µ to 80 µ), but they do not allow of the passage of worms.

The submucosa is profoundly changed; rigid and hard instead of supple. It is here that the greatest number of eggs occur. A remarkable condition of endophlebitis exists in the veins of the submucosa, not only in the smaller ones but also in the larger ones (370 µ by 270 µ). This endophlebitis results in a more or less complete occlusion of the vessels of the lumen.

The muscular coats are free from change, also their veins.

The Serous Coats.--The veins about 1,900 µ, also show endophlebitis. Besides the rectum, in extreme cases even the transverse colon, the cæcum and small intestine may be affected.

Bladder.--In the early stages the mucosa is deep red and swollen like velvet, or there may be localized patches of hyperæmia or extravasation. The subsequent changes take two chief forms:--

(1) Sandy Patches.--The mucosa looks as if it were impregnated with a fine brownish or yellowish powder (myriads of ova). This is accompanied by a gradual hypertrophy and new formation of connective tissue, so that dry, hard or plate-like patches with this sandy appearance arise; the thickening eventually affects all the coats of the bladder. In the older patches many of the eggs are calcified. These patches sooner or later break down, ulcerate and necrose. Phosphatic deposits are abundant and stone is common. These patches are not found in the rectum.

(2) Papillomata.--Where the inflammatory change produced by the eggs gives rise to hypertrophy and hyperplasia of the mucosa, papillomata result, the axis of which is formed by connective tissue of the submucosa. These are most variable in shape and form and bleed readily, and sometimes contain cavities of extravasated blood.

As in the rectum, it is in the submucosa that eggs are most abundant, and worms in copulâ occur in the veins of this layer, but endophlebitis is not as general as described in the rectum. Malignant disease of the bladder is not an uncommon sequela of bilharziasis. Besides the bladder, the ureters and kidneys may in advanced cases be involved. The prostate and vesiculæ seminales are commonly diseased. Eggs have been recorded in the semen. The urethra is frequently attacked; the vagina in the female.

Eggs also occur in the lymphatic glands of the gut.

Geographical Distribution.--East Africa: Nile Valley, Red Sea Coast, Zanzibar, Portuguese East Africa, Delagoa Bay, Natal, Port Elizabeth.

South Africa: Cape Colony, Orange Free State, Transvaal, Mauritius, Bourbon, Madagascar.

West Africa: Angola, Cameroons, Gold Coast, Gambia, Senegal, Sierra Leone, Lagos, Nigeria.

North Africa: Tripoli, Tunis, Algeria, parts of the Sahara.

Central Africa: Sudan, various portions. Uganda, Nyasaland.

It occurs with varying frequency in these regions. It is probably more widely spread than this list implies, as undoubtedly many cases are seen which are not recorded.

Isolated cases have been recorded from Arabia, India,[275] Greece, Cyprus.

[275] In a case from Madras, recorded by Stephens and Christophers, the eggs were long and spindle-shaped, quite unlike the eggs of Schistosoma hæmatobium.

The means by which infection is brought about are still uncertain; we only know that the miracidia (fig. 175) enclosed in the discharged eggs do not hatch if the eggs remain in the urine, but after cooling perish. As soon, however, as the urine is diluted with water the shell swells, generally bursting lengthways, and releases the miracidium from its investing membrane, so that it can swim about with the aid of its cilia. In its structure it differs but little from the miracidium of Fasciola hepatica, as, for instance, in the lack of eyes; the two large gland cells situated on either side of the intestinal sac are also present in the miracidia of Fasciola hepatica.

Sarcode Globules.--This is a term applied to certain globules which at times appear in the miracidium and are later ejected. Some authors consider them as indicative that the miracidium has developed into a sporocyst, but Looss considers them to be degeneration products.

The Bilharzia mission, under R. T. Leiper, sent to Egypt by the War Office early in 1915, reports that cercariæ of bilharzia type were recognized in four of the commonest fresh-water molluscs around Cairo.

With material obtained from naturally infected Planorbis boissyi acute bilharziosis was experimentally produced in rats, mice, and monkeys. Infection takes place experimentally through the skin and also through the mucous membrane of the mouth and œsophagus. The miracidium, after entering the mollusc, develops into a sporocyst. This gives rise not to rediæ, but to secondary sporocysts, which, in turn, produce cercariæ. These, like the adult worm, differ from other distomes in lacking a muscular pharynx.

*Schistosoma mansoni*, Sambon, 1907.

According to Manson, Sambon and others, the eggs with lateral spines belong to a species different from Schistosoma hæmatobium. Infections with this species only are said to occur in the Congo, Southern States of North America, West Indies (Guadeloupe) and Brazil (Bahia). The following characters, according to Flu, differentiate this species: (1) In the male the transition from the anterior portion of the worm to the lateral fields (the infolded portions which form the gynæcophoric canal) is not a gradual one as in Schistosoma hæmatobium, but in this case the lateral fields rise suddenly, almost at right angles to the anterior portion. (2) The ovaries have a well-marked convoluted course as in no other schistosome. (3) The oötype is symmetrical in reference to the long axis of the body, its duct being lateral on the ventral side (Looss’ explanation of this we have already given). (4) The worms live exclusively in portal vein and tract. (As lateral-spined eggs occur also in the bladder, this is not exactly true.)

------------------------------------------------------------------ |*Schistosoma hæmatobium*, Bilharz, 1852. | | | |Male, four or five large testes. Gut forks unite late, so that the| |single gut stem is short. Female, ovary in posterior half of body.| |Uterus very long, voluminous, with many terminal-spined eggs, some| |lying in pairs. Vitellaria in posterior fourth of body. Cercariæ | |in Bullinus contortus and Bullinus dybowski (syn.: Physa | |alexandrina) in Egypt. | | | | | |*Schistosoma mansoni*, Sambon, 1907. | | | |Male, eight small testes. Gut forks unite early, so that the | |single gut stem is very long. Females, ovary in anterior half of | |body. Uterus very short; usually only one lateral-spined egg at a | |time in utero. Vitellaria occupy posterior two-thirds of body. | |Cercariæ in Planorbis boissyi in Egypt. | | | |The above morphological descriptions are founded on worms of each | |species, derived from experimentally infected mice (Leiper, R. T.,| |Brit. Med. Journ., March 18, 1916, p. 411). | ------------------------------------------------------------------

*Schistosoma japonicum*, Katsurada, 1904.

Syn.: S. cattoi, Blanchard, 1905.

Male.--Eight to 19 mm., but extreme limits are 5 to 22·5 mm. Consists of a short fore-body, separated by the ventral sucker from the hind-body. The ventral sucker is stalked and somewhat larger than the oral sucker. Both suckers are larger than the corresponding ones in S. hæmatobium. Body usually smooth, but in the fresh state numerous fairly evident spines along the margin of the canal. Œsophagus: two bulbs. The junction of the gut forks more posterior than in S. hæmatobium, the median united gut stem occupying a quarter to one-fifth to one-sixth of the body length. An excretory canal runs along each side of the body, opening into the dorsal excretory pore. Testes irregularly elliptical, six to eight in number, in the anterior part of hind-body. The vasa efferentia unite into a common vas deferens which opens directly behind the ventral sucker. The seminal vesicle lies just behind this.

Female.--Up to 26 mm., generally thinner than the male. Surface smooth. Suckers armed with fine spines. Ventral sucker larger than oral. Body thicker behind the region of the ovary. The gut forks unite immediately behind the ovary. The united gut much thicker than in S. hæmatobium. Ovary elliptical, almost in the mid-body, its hinder portion dilated. The oviduct arises from its posterior end and then runs sinuously forward, where it is joined by the vitellarian duct; the vitellarium well developed, extending from behind the ovary almost but not quite to the posterior end as in S. hæmatobium. Shell gland ducts enter at the junction point of oviduct and vitelline duct. The canal here forms an oötype and then proceeds as the uterus to open directly behind the ventral sucker. The uterus occupies almost half the hind-body. In S. hæmatobium this is not so. The uterine canal is cleft-like, i.e., its dorso-ventral diameter is much greater than its lateral diameter. The number of eggs varies from about 50 to 300 from observations made in various hosts.

Eggs.--In utero assume various shapes, as they are soft; the lumen of the uterus is narrow. Outside they are oval, faint yellow, double contoured. In fæces the eggs measure 83·5 µ, by 62·5 µ (man); 85 µ by 61·5 µ (cattle); 98·2 µ by 73·8 µ (dog). The eggs have either small lateral spines or thickenings, and Looss at the opposite side has described cap-like thickenings. The eggs in the tissues undergo various deformities, and may contain a miracidium, as also the eggs in fæces do; or the contents may consist of granular matter or amorphous masses or they may be calcified. Lymphocytes and giant cells may also invade the eggs.

Mode of Infection.--The miracidia hatch in water in as little as fifteen minutes, but the majority in one to three hours. They will live in water for about twenty-four hours. In water they undergo a transformation into “larvæ,” which then penetrate the skin, as has been shown by Japanese writers to hold good for man, cattle, dog and cat. The penetration of the skin is attended with an eruption on the legs, “Kabure.” The exact route by which the worms reach the portal vein is uncertain. Infection in Japan takes place from spring to autumn, especially May to July, when the soil is contaminated with manure of cattle infected with S. japonicum. They also appear to develop in molluscs. Leiper and Atkinson found cercariæ (in sporocysts) in the liver of a mollusc, Katayama nosophora. They infected mice by immersing them in water containing liver emulsion and so free cercariæ, thus confirming the similar results of Miyairi and Suzuki.

Habitat.--The worm occurs in Japan, China, and the Philippines. The normal host is man and mammals. Cattle, dog and cat are often found naturally infected. Mice can also be experimentally infected. Their seat of election is the portal vein and its branches, especially the mesenteric veins. They either swim free in the blood or remain fixed by their suckers to the intima of the vessels. They have also been found in the vena cava and right heart of a cat, but not so far in the vesical plexus.

Eggs are found in the submucosa and mucosa of the gut, especially the colon, and at times in the serosa and subserosa of the small intestine, where they give rise to new growths. Occasionally eggs are found in the brain. The life of the worms is at least two years.

Pathogenic Effects.--Anæmia through loss of blood due to worms; enlarged spleen, toxic in origin (?); phlebitis, thrombosis, due to portal stasis; the eggs, however, cause the greatest mischief. They are carried by the circulation to various organs where they produce inflammation, granulation tissue, and later connective tissue.

Liver.--The eggs reaching this organ give rise to granulomata and hence enlarged liver, and later, when connective tissue is formed, to contraction. The surface is rough and irregularly granular, “parasitic embolic cirrhosis” of Yamagiwa.

Gut.--The eggs in the mucosa and submucosa cause catarrh and destruction of tissue or new growth. In the small intestine the eggs are mainly in the serosa and subserosa, where they give rise to polypoid or branched growths.

Spleen.--Enlarged, at first due to toxin (?) and later due to portal stasis. Eggs in the spleen are uncommon.

Ascites also arises from the portal stasis, and is generally present in advanced cases.

Eggs may be found in many other situations: glands (numerous), mesentery, stomach, pancreas, kidney, etc. The bladder remains free.

Class III. *CESTODA*, Rud., 1808.

Tapeworms have been known from ancient times--at all events, the large species inhabiting the intestines of man--and there has never been a doubt as to their animal nature. The large cysticerci of the domestic animals (occasionally of man also) have been known for an equally long period, but they were generally regarded as growths, or “hydatids,” until almost simultaneously Redi in Italy, and Hartmann and Wepfer in Germany, concluded from their movements and organization that they were of animal nature. From that time the cysticerci have been included amongst the other intestinal worms, and Zeder (1800) established a special class (Cystici, Rud., 1808) for the bladder worms. Things remained in this condition until the middle of the last century, when Küchenmeister, by means of successful feeding experiments, demonstrated that the cysticerci were definite stages of development of certain tapeworms. Before Küchenmeister, E. Blanchard, van Beneden, and v. Siebold had held the same opinion in regard to other asexual Cestodes.

Since the most remote period another question has again and again occupied the attention of naturalists, the question of the morphological nature--that of the INDIVIDUALITY OF THE TAPEWORM. The ancients, who were well acquainted with the proglottids (Vermes cucurbitani) that are frequently evacuated, were of the opinion that the tapeworm originated through the union of these separate proglottids, and this view was maintained until the end of the seventeenth century. In 1683 Tyson discovered the head with the double circlet of hooks in a large tapeworm of the dog; Redi (1684) was also acquainted with the head and the suckers of several Tæniæ. Andry (1700) found the head of Tænia saginata, and Bonnet (1777) and Gleichen-Rusworm (1779) found the head of Dibothriocephalus latus. Consequently most authors, on the ground of this discovery, considered the tapeworm as a single animal, that maintains its hold in the intestine by means of the head, and likewise feeds itself through it. The fact was recognized that there were longitudinal canals running through the entire length of the worm, and it was thought that these originated in the suckers, and that the entire apparatus was an intestine. As, moreover, the segments form at the neck, and are cast off from the opposite extremity, the tapeworm was also compared with the polyps, which were formerly regarded as independent beings.

Steenstrup, in his celebrated work on the alternation of generations (1841), was the first to give another explanation. This has been elaborated still further by van Beneden, v. Siebold and Leuckart, and until a few years ago all authorities adopted his views. According to this view, the tapeworm is composed of numerous individuals, something like a polyp colony, and, in addition to the proglottids--the sexual individuals which are usually present in large numbers--there is ONE individual of different structure, the scolex, which not only fastens the entire colony to the intestine, but actually produces this colony from itself, and therefore is present earlier than the proglottids. The scolex is a “nurse,” which, though itself produced by sexual means, increases asexually like a Scyphistoma polyp; the tapeworm chain has therefore been termed a strobila. Consequently the development of the tapeworms was explained by an alternation of generations. In support of this opinion it was demonstrated not only that the adult sexual creatures, the proglottids, can separate from the colony and live independently for a time, but that in certain Tæniæ, and especially in many Cestodes of the shark, the proglottids detach themselves long before they have attained their ultimate size, and thus separated continue to develop, grow and finally multiply; the scolex also exhibits a certain independence in so far as, though not, as a rule, capable of a free life, yet it in some cases lives as a free being, partly on the surface of the body of marine fishes and partly in the sea. With the more intimate knowledge of the development of the cysticerci, the independent nature of the scolex was recognized. It is formed by a budding of the bladder that has developed from the oncosphere, in some cases (Cœnurus) in large numbers, in other cases (Echinococcus) only after the parent cyst has developed several daughter cysts. Released from its mother cyst and placed in suitable conditions, it goes on living, and gives rise at its posterior end by budding to the strobila, the proglottids of which eventually become sexual individuals.

In order to make this clearer we will briefly summarize what takes place in the jelly-fishes.

By metamorphosis is meant a developmental change in the same individual, while alternation of generations, or metagenesis, implies a stage in which reproduction of individuals takes place by a process of budding or fission. This asexual reproductive stage alternates with the sexual mode of reproduction. Thus in the development of the Scyphozoa (jelly-fishes) we have:--

(1) The fertilized egg cell divides regularly and forms a morula.

(2) By accumulation of fluid in the interior this becomes a closed sac with a wall formed of a single layer of cells, forming the blastosphere or blastula.

(3) One end of the sac is invaginated, forming a gastrula.

(4) The gastrula pore or mouth closes, forming again a sac, the walls of which have two layers, forming a planula.

(5) This becomes fixed to a rock, an invagination forms at one end, a depression--the stomodæum--communicating with the enteric cavity. Tentacles grow out and we have a Scyphozoön polype, Scyphistoma or Scyphula. It is to this stage that Steenstrup gave the name “nurse” (“wet-nurse”), because it nourished or produced asexually the succeeding forms.

(6) Asexual reproduction by transverse fission occurs in this, forming a pile of saucer- or pine-cone-like animals which before this time had been considered to be a distinct animal, which was called strobila from its resemblance to a pine-cone. This is the alternate generation.

(7) The individuals of the strobila become free and are called Ephyrulæ.

(8) These develop finally into adult sexual jelly-fish, Scyphozoa, so that comparing a tapeworm with this we have (a) egg, (b) scolex (= Scyphula or “nurse”), (c) asexual reproduction of the tapeworm chain (= strobila), (d) development of the individuals of the chain (proglottids) into sexual adults.

Van Beneden’s terminology for these stages is the following: Ciliated embryo = protoscolex; scyphistoma = deutoscolex (or scolex); free Ephyrula = proglottis. According to this view, as is the case in many endoparasitic Trematodes, asexual reproduction by budding occurs at two stages of the whole cycle of development, viz. (1) in the formation of the scolex by budding from the bladder (“nurse”), (2) in the formation of the strobila by budding from the scolex (“nurse”).

But in cysticercal larval forms it appears that the scolex does not arise in this way but is simply a part of the proscolex (hexacanth embryo), becoming invaginated into it for protection, so that there is no asexual gemmation here. It has been questioned also whether the strobila also arises by gemmation. If it does, the tapeworm is a colony of zoöids produced by budding from the asexual scolex; if it is not produced in this way, then the tapeworm is to be regarded as an individual in which growth is accompanied by segmentation. Against the “colony” view are the facts that the muscular, nervous, and excretory systems are continuous throughout the worm, and that some tapeworms, such as Ligula, are unsegmented.

Finally, if the tapeworm is an individual the question arises which is the head end. As new segments are formed at the neck, and as this point in annelids is the antepenultimate segment, the scolex must be the last or posterior segment. The caudal vesicle or bladder of larval forms is consequently anterior. According to this view, in tapeworms as among many endoparasitic flukes, an asexual multiplication occurs at two points of the whole cycle of development, which is as follows: (1) egg, (2) oncosphere or hexacanth embryo, (3) bladder (cysticercus or hydatid), (4) (after digestion of the bladder) by budding, the scolex, (5) by budding from the scolex the sexual proglottids, (6) the egg; (4) and (5) being the two asexual stages.

ANATOMY OF THE CESTODA.

If we except the tapeworms with only one proglottis, the CESTOIDEA MONOZOA, Lang = Cestodaria, Monticelli, we can always distinguish in the Cestodes, in the narrower sense, one scolex or head and a large or small number of segments (proglottids). The SCOLEX serves the entire tapeworm for fastening it to the internal surface of the intestinal wall, and therefore carries at its end various organs which assist in this function, and which are as follows: (i) SUCTORIAL ORGANS, i.e., the four suckers (acetabula), which are placed crosswise at the circumference of the thickened end of the scolex; further, the double or quadruple groove-like suckers (bothridia), which are diversely shaped in the various genera and families.[276] (2) FIXATION ORGANS (hooklets)[277] that likewise occur in varying numbers and different positions; they may be in the suckers, or outside them on the apex of the scolex; for instance, in many of the Tæniidæ they appear in a circle around a single protractile organ, the rostellum, or the latter may be rudimentary, and is then replaced by a terminal sucker. (3) PROBOSCIS. One family of the Cestodes, the Rhynchobothriidæ, carries four proboscides, moved by their own muscular apparatus, on the scolex, and they are beset with the most diverse hooks. (4) TENTACLE-LIKE formations are only known in one genus (Polypocephalus).

[276] They may remain simple, and are then not separated from the remaining muscles of the scolex; or they project as roundish or elongated structures over the scolex, hollow on their free surface, and often divided into numerous areas by muscular transverse ribs. They may also carry accessory suckers on their surface.

[277] The various parts of a hooklet are thus named from the point backwards: (1) blade or prong, (2) guard or ventral or posterior root, (3) handle or dorsal or anterior root.

The thickened part of the scolex that carries the suckers is usually called the head; the following flat (unsegmented) part connecting it with the proglottids is called the neck, and is sometimes quite small. In a few cases the entire scolex (or head) disappears, and its function is then undertaken by the contiguous portion of the chain of proglottids, which is transformed into a variously shaped PSEUDO-SCOLEX.

The proglottids are joined to the scolex in a longitudinal row, and are arranged according to age in such a manner that the oldest proglottis is farthest from the scolex, and the youngest nearest to it.

The number of segments varies, according to the species, from only a few to several thousands; they are either quadrangular or rectangular; in the latter case their longitudinal axis falls either longitudinal or transverse to that of the entire chain, according as the segments are longer than broad or broader than long. When the number of segments is very large, the youngest ones are, as a rule, transversely oblong, the middle ones are squarish, and the mature ones longitudinally oblong. The posterior border of the segments, as a rule, carries a longitudinal groove for the reception of the shorter anterior border of the following proglottis. The two lateral borders of the segment are rectilinear, but converge more or less towards the front, or they are bent outwards. In most of the Cestodes the segments, just as the neck, are very flat; in rare cases their transverse diameter is equal to their dorso-ventral diameter. As a rule the segments, singly or several united together, detach themselves from the posterior end, in many cases only after complete maturity is attained, and in others much earlier; they then continue to live near their parent colony, to still call it by that name, in the same intestine and continue their development. Even when evacuated from the intestine the proglottids under favourable circumstances can continue to live and creep about, until sooner or later they perish.

The first proglottis formed, and which in a complete tapeworm [i.e., sexually complete] is the most posterior, is as a rule smaller and of different shape, it also frequently remains sterile, as likewise happens in the next (younger) segments in a few species; otherwise, however, sooner or later the generative organs develop in all the segments, mostly singly, sometimes in pairs; in the latter case they may be quite distinct from each other or possess some parts in common. The term “mature” is used for a proglottid that has the sexual organs fully developed, while “gravid” is used for one containing eggs. Most of the species combine male and female genitalia in the same segment, only a few are sexually distinct (Diœcocestus). In the hermaphrodite species one male and one female sexual orifice are always present, and, in addition, there may be a second female orifice, the uterine opening; as a rule, however, this is lacking, and in one sub-family, the Acoleinæ, to which also the genus Diœcocestus belongs, the other sexual orifice, the opening of the vagina, is also absent. The position of these orifices varies; the cirrus and vagina usually open into a common atrium on one lateral border or on a surface of the segments; the orifice of the uterus may be on the same surface or on the opposite one.

The surface on which the uterus opens is termed the VENTRAL SURFACE; if this orifice is absent, one must depend on the ovary, which almost always approaches one of the two surfaces; this surface is then called the ventral.

The length of the Cestodes--independently of their age--depends on the number and size of the segments, as well as on their contraction; the smallest species (Davainea proglottina) is 0·5 to 1·0 mm. in length; the largest may attain a length of 10 m., and even more.

The entire superficial surface of the tapeworms is covered with a fairly resistant and elastic layer, which exhibits several indistinctly limited layers and which is usually called a cuticle, which also covers the suckers, and is reflected inwardly at the sexual orifices. In some species fine hairs appear, either on the entire body or only in the region of the neck, on the external surface. In the cuticle there can be recognized, besides the pores, which no doubt are concerned with nutrition, spaces in which lie the ends of sensory cells. Close under the cuticle lies the external layer of the parenchyma (basal membrane), and below this the circular and longitudinal muscles forming the dermo-muscular coat. The matrix cells of the cuticle occur as in the Trematodes, only on the inner side of the peripheral muscles in the external zone of the parenchyma; they are fusiform cells, forming one or two layers, but are not arranged in the manner of epithelial cells (fig. 184, Sc.c.). They have fine branching processes which run between the dermal muscles, pass through the basal membrane and penetrate the internal surface of the cuticle with small pistil-like enlargements, expanding on the internal surface of the cuticle into a thin plasma layer.

In addition to the above mentioned, there are other cuticular formations occurring on the cuticle of some Cestodes, such as immobile hairs and variously formed hooks, such as are seen principally on the scolex. Their development is only roughly known in a few species; they are usually already present in the larval stage, and of the same arrangement and shape as in the fully developed tapeworms; a matter of importance, because by these structures larvæ can be recognized as being those of a certain species of tapeworm.

The CUTICULAR GLANDS in Cestodes are scarce.

The PARENCHYMA forms the chief tissue of the entire body, and in all essentials its structure is similar to that of the Trematodes.

The same doubt exists here also as to the nature of the parenchyma. Recent authors consider that it consists of highly branched cells, the processes of which ramify in all directions. These cells lie in a non-cellular matrix containing fluid vacuoles. This matrix spreads in between and so breaks the continuity of the epidermal cells.

In the parenchyma of almost all the Cestodes there are found in adult specimens, as well as in larvæ, light-refracting concentrically striated structures, of a spherical or broad elliptical shape, which, on account of their containing carbonate of lime, are termed CALCAREOUS CORPUSCLES (fig. 184, C.). Their size, between 3 µ and 30 µ, varies according to the species; their frequency and distribution in the parenchyma also varies, but they are chiefly found in the cortical layer. They are the product of certain parenchymatous cells, in the interior of which they lie like a fat globule in a fat cell, but according to others they are intercellular in origin.

The MUSCULAR SYSTEM of the proglottids is composed of--(1) the subcuticular muscles (figs. 184 and 185), as a rule consisting of a single layer of annular muscles; (2) longitudinal muscles; (3) dorso-ventral fibres extending singly from one surface to the other, and at both ends expanding in a brush-like manner, and inserted into the basal membrane, consisting of an outer, more numerous, and an inner, less numerous but more powerful layer (the number of bundles in this layer being in certain cases of specific importance); (4) transverse fibres, the elements of which penetrate to the borders of the segments, thus passing through the longitudinal muscles and reaching the cuticle. In the region of the septa the transverse and dorso-ventral muscles form a kind of plate.

The mass of parenchyma bounded by the transverse muscles is termed the MEDULLARY layer, while the mass lying outside them is termed the CORTICAL LAYER.

It was known long ago that the myoblasts adhere to the dorso-ventral fibres as thickenings, but it is only recently that large star-shaped cells (fig. 184), separated from but connected with them by processes, have been recognized as the myoblasts of other fibres (Blochmann, Zernecke).

Within the scolex the direction and course of the muscular layers change.

The SUCKERS are parts of the musculature, locally transformed, with a powerful development of the dorso-ventral muscles, now become radial fibres.

The ROSTELLUM of the armed Tæniæ, like the proboscis of the Rhynchobothriidæ, also belongs to the same category of organs.

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