Manson's tropical diseases : a manual of the diseases of warm climates

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MANSON'S

Preface To The Seventh Edition

8ince the publication of the Sixth Edition- of this work, in 1917, many advances in Tropical Medicine have been made, and much that before was vague and hypothetical has become precise and been either confuted or confirmed. Much of this is attributable to experience in the Great War.

Outside the war zone scientific workers have not been idle. Noguchi and his fellow-countrymen have described a new group of parasites — the Leptospiras, which are probably responsible for yellow fever, Weil’s disease, and allied fevers of hitherto unknown etiology. They have been equally diligent and suc¬ cessful in elucidating other important problems, especially in helminthology.

Of recent years the subject of tropical fevers has greatly ex¬ panded, and it has been found necessary to devote twenty-three chapters of the Manual to this group of diseases. Recent additions to our knowledge of the enteric group have been incorporated in what is virtually a new chapter, for much of which I am indebted to Dr. R. P. Garrow.

In providing for these and other subjects, it has been necessary to rearrange and rewrite a considerable portion of the book, and to find room for a mass of technical detail in a series of Appen¬ dices devoted to Protozoology, Medical Zoology, and Laboratory Methods. Though they are not intended to take the place of more exhaustive treatises on these subjects, I feel that the inclusion of

V

Vi PREFACE TO THE SEVENTH EDITION these Appendices will be of service to the student, and especially to the isolated worker in the Tropics.

In order to render them complete, I have not scrupled to repeat, or to amplify, facts already set out in the text, so that those who use the Appendices may find in them all the information they require.

Major Austen, D.S.O., has kindly revised the section dealing with Tse-tse Flies.

In threading the mazes of Medical Protozoology I have bene¬ fited by the advice of Professor Clifford Dobell, F.R.S.

Dr. Andrew Balfour, C.B., C.M.G., and his associates atj *the Wellcome Bureau of Scientific Research have afforded assistance on many difficult points.

From my colleagues at the London School of Tropical Medicine I have received similar sympathetic help.

I desire also to acknowledge the loyal and devoted help of my former assistants, Mr. W. J. Muggleton and Mr. T. R. Goddard, in the preparation of the Laboratory Appendix. To the latter gentleman I am to a great extent indebted for a description ^of a method of performing the Wassermann reaction suitable for the Tropics.

A large number of new Plates and Figures in the text have been added. To Dr. J. Gordon Thomson I am indebted for the fine colour drawing illustrating the Malaria Parasites (Plate I.). The originals of Plates II., IV., V. were painted by Dr. J. K. Lund, who has been good enough to place his artistic skill at my service. Dr. John Bell has kindly supplied a number of valuable microphotographs.

To Dr. Eric Bellingham-Smith I am indebted for a selection of typical temperature charts.

PREFACE TO THE SEVENTH EDITION vii

Special acknowledgment must be made to Professor Brumpt, to Professor Nuttall, F.R.S., to the Editors of the Journal of Experimental Medicine , to the Editors of the Journal of Parasitology , and to the Trustees of the British Museum and of the Rockefeller Foundation, for permission to adapt or other¬ wise make use of illustrations that have appeared in their publications.

These acknowledgments would be incomplete without special reference to Dr. A. G. Bagshawe, the Editor of the Tropical Diseases Bulletin ; but for the aid of that publication my task would have been impossible.

I have felt it a great honour that the charge of this famous Manual should have been entrusted to me. It is difficult for me to express adequately the debt I owe to the original author, Sir Patrick Manson, who has given freely of his ripe experience in revising proofs and making many valuable suggestions.

Dr. John Anderson has kindly read through the final proofs.

To prevent the work from becoming unduly bulky, the Pub¬ lishers have enlarged the page and the type has been entirely reset. It is a pleasure to acknowledge their unfailing courtesy and helpfulness.

Philip Manson-Bahr.

Weymouth Street , W .

January , 1921.

Preface To The First Edition

A manual on the diseases of warm climates, of handy size, and yet giving adequate information, has long been a want ; for the exigencies of travel and of tropical life are, as a rule, incompatible with big volumes and large libraries. This is the reason for the present work.

While it is hoped that the book may prove of practical service, it makes no pretension to being anything more than an intro¬ duction to the important department of medicine of which it treats ; in no sense is it put forward as a complete treatise, or as being in this respect comparable to the more elaborate works by Davidson, Scheube, Rho, Laveran, Corre, Roux, and other systematic writers in the same field.

The author avails himself of this opportunity to acknowledge the valuable assistance he has received, in revising the text, from Dr. L. Westenra Sambon and Mr. David Rees, M.R.C.S., L.R.C.P., Superintendent, London School of Tropical Medicine. He would also acknowledge his great obligation to Mr. Richard Muir, Pathological Laboratory, Edinburgh University, for his care and skill in preparing the illustrations.

ix

Section I. — Fevers CHAPTER PA<JR

2. Description of the Various Species of Malaria

Parasites and their Associated Fevers . . 27

3. Epidemiology and Endemiology of Malaria . . 56

4. Diagnosis, Treatment, and Prophylaxis of Malaria 62

5. Malaria and the Mosquito . 83

7. Trypanosomiasis of Man . Ill

11. Infectious Jaundice . 211

12. Rat-bite Fever . 217

13. Seven-day Fever . 219

15. Phlebotomus Fever . 230

16. Spotted Fever of the Rocky Mountains . . 235

17. Japanese River Fever . 241

18. Typhus Fever in the Tropics . 246

21. Enteric and Enteric-like Fevers in the Tropics . 291

23. The Diagnosis of Fevers in the Tropics 327

xi

CONTENTS xii

Section V. — Animal Parasites and Associated Diseases

40. Parasites of the Circulatory System : Schistosomiasis 553

41. Parasites of the Lymphatic System and Connective

Tissues : Filariasis . 581

42. Parasites of the Lymphatic System and Connective

Tissues : Filariasis (concluded) .... 631

43. Parasites of the Lung and Liver : Paragonimiasis ;

Clonorchiasis . 647

£ £2

CONTENTS xiii

Section VI. — Diseases due to Poisons, including Snake-bite PAUK

Vegetable Poisons ....... 679

Animal Poisons . 684

Section VII. — Tropical Skin Diseases

47. Non-specific, Bacterial, Fungous Diseases, etc. . 693

Section VIII. — Local Diseases of Uncertain Nature

48. Craw-craw — Chappa — Climatic Bubo — Goundou —

Ainhum — Bio Heel — Onyalai .... 738

Appendix I. — Medical Protozoology

Sarcodina . 749

Mastigophora . 755

Sporozoa . 770

Ciuophora . 782

Spirochetes . 782

Appendix II. — Medical Helminthology, Entomology, etc.

Phylum Platyhelminthes . 784

The Trematoda . 784

The Cestoda . 804

Phylum Nemathelminthes . 819

The Nematoda ....... 819

The Gordiacie . 849

The Acanthocephala ..... 850

Phylum Annelida . 851

Phylum Arthropoda . 852

The Arachnida . 853

The Insecta . 863

CONTENTS

PAGE xiv

Classification of Snakes (Order Ophidia) . . 872

Colubride . . . 873

Viperide . # . 874

Appendix 111. — Laboratory Methods as applied to Clinical Medicine in the Tropics

lf Cleaning Slides and Cover-slips .... 878

2. Methods of Preparation of Blood-films . . 878

3. Staining of Blood-films for Protozoa and for the

Differential Count of Cells . 881

4. Measurement of Microscopic Objects . . . 884

5. Varieties of Blood-cells, and their Significance . 885

6. Enumeration of Blood-cells and Estimation of

Hemoglobin . 887

7. Preparation of Useful Culture Media . . . 888

8. Cultivation of Protozoa and Bacteria from the

Blood, Cerebro-spinal Fluid, etc. . . . 895

9. Agglutination with Patient’s Serum for Typhoid,

Paratyphoid, and Weil-Felix Reaction 897

10. Recognition of Organisms isolated from the

Feces and Urine by Agglutination . . 902

11. Chemical and Microscopical Examination of Feces 903

12. Examination of Urine in the Tropics . . . 908

13. Spectroscopic Examination of Urine and other

Fluids . 909

14. Detection of Spirochetes, Spironemes, and the

Gonococcus . 910

15. A Practical Method of performing the Wasser-

mann Reaction, suitable for the Tropics . 913

16. Fixation of Tissues for Paraffin Sections . . 920

17. Preservation of Tissues for Museum Purposes . 924

18. Rearing, Dissecting, and Preserving Mosquitoes . 925

19. Formule of Stains commonly in Use . . . 928

20. Scales and Standards . 931

INDEX . 935

LIST OF PLATES

FACING PAQB

1. Malaria Parasites (colour) . 32

2. The Blood Picture in Quartan and Mixed Infec¬

tions (colour) . .34

3. Benign Tertian Malaria . 36

4. The Blood Picture in Benign Tertian Malaria (colour) 38

5. The Blood Picture in Subtertian Malaria (colour). 40

6. Subtertian Malaria : Sections of Brain and Liver

7. Two Well-known Malaria-carrying Anopheles (colour)

8. Blackwater- Fever Urine (colour) ....

9. CONORHINUS MEGISTUS (colour) .

10. Tse-tse Flies (colour) .

11. Parasites of Kala-azar and Oriental Sore (colour)

12. Ticks (colour) . .

13. Stegomyia fasciata (colour) .

14. Dengue Rash (colour)

15. Pellagra (colour) .

16. Pellagra Rash on Feet .

17. Intestinal Lesions in Amcebic and Bacillary Dys¬

entery (colour) ......

18. Microscopical Section of the Large Intestine in

Bacillary Dysentery .....

19. Sprue Tongue (colour)

XV

XVI

LIST OF PLATES

FLATK rACINO

20. Early Macular Rash of Leprosy (colour)

21. Schistosoma Eggs .

22. Schistosomiasis of the Far East ....

23. Microfilaria of the Blood (colour) ....

24. Stegomyia pseudoscutellaris (colour)

25. Distinguishing Features between mf. bancrofti

AND MF. LOA, IN STAINED SPECIMENS (colour) . '

26. Tinea Imbricata . . '

27. Normal and Abnormal Blood-cells (colour) j k brown, blackish brown, or ore or less dark), in G, austeni Upper? <^ar^er tban rest

Jroup IV

Wings fair; l»lpi (exce| tooaniformi and slen

Group

All tarsi uni¬ formly black, wings very dark

G. tiemanni.

Glossina IV

▲lpalis Group longest hai

front mar-- -

of antenn! ^ • ,

to Jrd wic Dorsum of ab-

palpi of me domen buff» 3rd and other segments ex¬ hibiting ingest hairs of 3rd joi finfdinterfrom 1 to j ruPtedutra"8- segment verse bands

G. tachinoide*.

Fringe on fron joint of ante to be scare* pleurae drab¬ line, hind co:

Dorsum of abdomen ochraceoustawny, with at least a trace of dark transverse bands, widely interrupted, and not sharply de¬ fined

G. austeni.

Fleura dark gr mouse-grey

deflnis as yet uncertain ; although In some respects resembling reoorded only from Cameroon, cannot be assigned to a

TROPICAL DISEASES

Chapter I Malaria

Definition. — Morbid conditions produced by certain protozoal parasites belonging to the class Sporozoa, whose definitive host is the mosquito, and whose intermediate host is man. In man these parasites inhabit the red blood-corpuscles, giving rise to fever — usually of a periodic character, anaemia, enlargement of the spleen, and the deposit of a black pigment in the viscera and elsewhere. Some of their phases are amenable to quinine.

History

The history of malaria goes back to times of remotest antiquity. Already in the fifth century b.c. Hippocrates recognized the exist¬ ence of periodic fevers, and divided them into quotidian, tertian, subtertian, and quartan.

The introduction of cinchona in 1640 enabled Morton and Tort to separate the malarial fevers from other febrile diseases, and to show that some continued and remitting fevers belong to the same group as the intermittents.

The next important step was the discovery of the characteristic pigmentation of the viscera in malaria. Certain pigment-bearing cells found in the spleen were described by Meckel in 1847, and their presence in the peripheral blood was later confirmed by Virchow and Planer.

The parasitic nature of malaria was definitely established by Laveran, who in 1880, having noticed the eruption of long motile filaments from the pigmented cells, first recognized their parasitic character.

Laveran’s observations were soon extended by Marchiafava, Celli, Golgi, Bignami, Bastianelli, and other investigators.

Manson, impressed by the fact that a certain and very active

B

[CHAP.

phase of the parasite was evolved, not while in the human body, but only when the blood containing the parasite had been removed from the human body, concluded that this phase represented the first step in its extracorporeal life ; and he further reasoned from the analogy of other hsemoparasites and from ascertained epidemio¬ logical facts that certain species of mosquito were the agents that removed the parasite from the human body, and were the medium in which biological changes necessary for qualifying the parasite for re-entrance into a human host were effected. Ross’s investi¬ gations on the lines suggested by Manson definitely established the accuracy of his hypothesis, and proved that the mosquito not only recovered from the human body the parasites, but also that it implanted them into the human host.

Finally, the application of these recent discoveries to the diagnosis and prevention of malaria has led to practical measures which have already been fruitful in good results and promise yet more.

Proofs that the Malaria Parasites are the Cause of Malarial Disease

It is now placed beyond doubt that the presence and prolifera¬ tion in the blood of these parasites are the cause of what was formerly and is still known as “ malarial disease.” The reasons for this statement are now sufficiently well known. They are based upon the well-ascertained facts that the phenomena of malarial fever are invariably associated with parasites in the blood ; that intra¬ venous injection of parasite-containing blood into a normal in¬ dividual is followed, after a period of 10-12 days, by an attack of fever and the appearance of the same species of parasite in the blood .of the person thus injected ; that the parasite undergoes developmental changes in the bodies of certain anopheline mos¬ quitoes, and can be demonstrated at a later date in the salivary glands ; that such a mosquito can convey the infection to a second individual after a definite incubation period ; and further, that the drug quinine, which cures malarial disease, causes the parasites to disappear from the blood.

The proof of the causal relationship of the parasite to the disease may therefore be said to be complete.

Morphology and Histology

There are three species of malaria parasites. The distinctive characteristics of each of these will be detailed later. The following brief description is confined to what may be regarded as the generic features common to all.

I]

THE PARASITE: HUMAN CYCLE

The three phases. — -The malaria parasite, like all true parasites, must be adapted not only for a life inside its hosts, but also, in order that its continuance as a species may be assured, for a passage from one host to another. Consequently, as regards man, it exhibits two distinct phases — an intracorporeal and an extracorporeal. Clinical observation and analogy make it certain that there is yet another phase, also intracorporeal — the latent phase, whose characters as yet can only be conjectured.

INTRACORPOREAL OR HUMAN CYCLE

Each species of malaria parasite has its special and more or less definite intracorporeal life-span or cycle of, approximately, forty-eight hours, or seventy-two hours.

(see text).

On examining microscopically malarial blood towards the end of one of these cycles, an hour or two before the occurrence of a paroxysm of the characteristic periodic fever it induces, the parasite may be recognized as a pale, somewhat ill-defined disc of protoplasm occupying a larger or smaller area within a proportion of the red blood -corpuscles (Fig. 1, a). Scattered through this pale body are a number of intensely black or reddish-black particles — an excrementitious material called hamozoin.

Changes in the parasite. — The changes the parasite under¬ goes may be followed by making repeated examinations of the blood at frequent intervals. As the parasite matures, the haemozoin collects into central blocks round which the pale protoplasm of the parasite arranges itself in minute segments. The including corpuscle breaks down and liberates the spherules, or spores, none of which contains hamozoin. A proportion of the spores, escaping phagocytosis, attach themselves to other red blood-corpuscles, which they contrive to enter. In the interior of these

[CHAP.

newly infected corpuscles the young parasites grow at the expense of the haemoglobin, and exhibit active amoeboid movement. By appropriate staining the free spherules are found to consist of a nucleolus (a deeply tinted chromatic mass, surrounded by a vesicular nucleus), and this again by a lightly tinted covering of protoplasm. As the parasite grows and approaches maturity, the nucleolus enlarges, becomes less defined, and then disperses ; finally, just before sporulation both nucleus and nucleolus cease to be distin¬ guishable (Fig. 2, a, j).

At this stage these elements become fragmented and diffused throughout the protoplasm. Later the nuclear elements reappear as numerous minute, scattered nucleoli ; and it is around these that the protoplasm of the segmenting parasite arranges itself to form the spherules (Fig. 2, b, c). The vesicular character of the

Fig. 2. — Evolution of the tertian parasite, stained ( see text).

nucleus does not usually appear in the spherules until after these have become free in the liquor sanguinis (Fig. 2, d).

The haemozoin particles, so characteristic of the malaria parasite, occur as black or very dark-red dust-like specks, coarse grains, or short rods, either isolated or aggregated into larger or smaller, more or less dense clumps. Until the concentration of haemozoin which precedes the formation of spherules takes place the particles are scattered, being located principally in the outer zone, or ectosarc, of the parasite. Apparently, so long as the nucleus remains entire the haemozoin is peripheral ; when segmentation occurs in the nucleus the haemozoin becomes central.

Such is a brief account of the cycle and structure of one phase of the parasite. From it we may understand how the parasite maintains itself and multiplies inside the human body. It does not explain, however, the two other important biological features which analogy and observation clearly indicate — namely, its latency in, and its life outside, the human body.

FLAGELLATED BODIES i]

EXTRACORPOREAL OR MOSQUITO CYCLE

The problems suggested by the question of an extracorporeal cycle for the malaria parasite are — first, how does the parasite leave the human body ; second, what is its life when temporarily outside the human body ; and, third, how does the parasite re-enter the human body ?

The flagellated body. — When fresh malarial blood is exam¬ ined some time after it has been mounted as a wet preparation, it is no unusual thing to see what is known as the “ flagellated body (Fig. 3). Analogous bodies are found in aU forms of y moo dm Muir

Fig. 3. — Malaria parasite : flagellated body, stained.

malaridy both in those special to man and in the corresponding infections of other vertebrata. It is a strange-looking, octopus¬ like creature with long, actively moving arms. Though composed of the same materials — namely, colourless protoplasm and dark luemozoin granules — it differs in many respects from the ordinary forms of the parasite, more especially in the fact that it is not intracorpuscular, but free in the liquor sanguinis. The long, whip¬ like arms, numbering from one to six, or even more, are usually designated flagella or, more correctly, microgametes. These are

• The expressions “ flagellated body ” and “ flagellum,” applied to tTiis phase of the malaria parasite, though graphic enough, are somewhat misleading. The flagella of the malaria parasite are in no sense analogous to the flagella of the flagellata ; they really function as spermatozoa. The proper zoological terms for this and the other phairrr of the malaria parasites are given at p. 19.

[CHAP.

exceedingly delicate and pliant filaments, difficult to see not only on account of their delicacy but also on account of the rapidity of their movements. Occasionally it may be observed that one or more of the microgametes break away and may be seen swim¬ ming away with vibratile and undulatory movements. (Fig. 4.)

It is of importance to bear in mind that these flagellated bodies are never seen in newly drawn blood, and that they come into view only after the slide has been mounted for some time — ten to thirty minutes, or even longer, according to circumstances.

Source of the flagellated body. — Careful observation shows that the flagellated bodies are developed from a particular phase

Fig. 4. — Malaria parasite ; flagellated body [and free-swimming microgamete.

of the intracorpuscular parasite, a phase which ^differs in form according to species — namely, in the subtertian type from what is known as the “ crescent body ” ; in other types from certain analogous intracorpuscular parasites closely resembling the mature parasite (Fig. 2, j) just prior to concentration of haemozoin and segmentation.

The crescent body. — These mature parasites are never found in the blood at the commencement of a malarial attack, but only after 7-10 days ; they are not affected by quinine. They may be very numerous, several in every field of the microscope, or so scanty that many preparations may have to be searched before one is found. Not infrequently they cannot be discovered at all ; especially is this the case in malignant (subtertian) infections in

CRESCENT BODIES i]

the tropics, although, strange to say, when the same patients suffer a relapse in Europe it is generally easy enough to find .the crescent body in the blood.

The shape, size, and structure of the crescent body can best be comprehended from the illustrations (Figs. 5, 6). It exhibits Ho amoeboid movements. The principal features to be noted are its very definite crescentic shape ; the probable existence of a delicate limiting membrane ; the presence of needle-shaped haemozoin particles, usually about the centre of the parasite, though sometimes nearer one end ; and a bow-like and exceedingly delicate line that, springing from a point somewhat inside the roundedoff tips of the- horns of the crescent, bridges its concavity. Manifestly this bow represents the outline of the remains of the blood-corpuscle in which the parasite had developed/ Very rarely twin or double crescents — that is, two crescents in one corpuscle — are encountered (Fig. 5).

Crescents differ in appearance accord¬ ing to their age ; in some the haemozoin granules are scattered throughout the parasite, in others they are concentrated, and in a third class the protoplasm shows vacuolation and other signs of degenera¬ tion. By dissolving the haemozoin particles Fig. 5. — Malaria paraat the centre of the crescent with weak 8ite : twin crescents, solution of ammonia, and subsequently staining, a nucleolus, sometimes double, can be demonstrated.

As will be shown in the sequel, these crescent bodies and the large intracorpuscular forms just alluded to are sexual in their functions. As regards the crescents, there are certain differences in the appearance of the protoplasm, in the arrangement of the pigment, and in the characters of the nucleus as revealed by staining, which are distinctive of the male and female crescents respectively. In one type of crescent the protoplasm is hyaline and the haemo¬ zoin somewhat loosely arranged ; in another type the protoplasm is faintly granular and the haemozoin more concentrated, being arranged as a well-defined ring about the centre of the parasite. The former is male, the latter female. The protoplasm of the male parasite stains less deeply, and its nucleus is larger than that of the female parasite.

The more immature forms of the crescent are said to begin to be recognizable in the spleen and bone-marrow about the fourth day after a subtertian malarial attack commences. At first they

[CHAP.

are minute, highly refringent amoeboid bodies. They are rarely encountered in peripheral blood ; there the crescent body does not begin to show itself till it approaches maturity, about a week after the first crop of amoeboid parasites associated with the fever paroxysm has appeared.

Formation of the flagellated body from the crescent in subtertian, and from the large intracorpuscular parasites in quartan and tertian malaria. — If a number of crescent bodies are kept under observation a certain proportion will be seen to become gradually converted into spheres (Fig. 7, a, b, c). The

Fig. 6. — Female crescent in subtertian malaria. X 1,000.

(Microphoto : Dr. A. Norman.)

remains of the enclosed blood-corpuscles fall to pieces or melt away. The ensuing sphere is now known to be of two sexes, some — the male — having hyaline, others — the female — having granular protoplasm. After a time, in the case of the former, the haemozoin particles become violently agitated and are diffused through the sphere, and one or more filaments are shot out from the periphery and indulge in wavy or lashing movements (Fig. 7, e).*

* Careful’focusing, especially of stained crescent-derived spheres, may sometimes show that for a short time before their eruption the microgametes exist preformed inside the limiting membrane of the sphere (Fig. 7, c). One can sometimes see a micro¬ gamete filament, in its efforts to erupt, carry this.membrane in front of it, and, failing to break through, retract and perhaps renew the effort at another point. Doubtless the agitated movements of the sphere are produced by the efforts made by the micro¬ gametes to break through this membrane.

i] FORMATION OF FLAGELLATED BODY 9

The granular spheres, or the female element, do not project fila¬ ments, or microgametes. In stained specimens the microgametes are found to be composed of two elements — a chromatic filament enclosed in a covering of protoplasm. Should the microgametes succeed in breaking away, the remains of the flagellated body

Fig. 7. — Evolution of the flagellated body from the crescent.

consist of hfemozoin particles included in a small amount of residual protoplasm.

In quartan and benign tertian malaria certain bodies (Fig. 8, a , d), which, but for the brisk movements of their haemozoin, look like ordinary full-grown intracorpuscular parasites prior to a b c

Fig. 8. — a. 6, c , Evolution of the flagellated body in tertian fever; d, e, f, evolution of the flagellated body in quartan fever.

the formation of spores, may sometimes be seen to slip out from their enclosing corpuscles (Fig. 8, 6, e). If these free parasites are watched, in some instances the haemozoin they contain is seen to indulge in violent dancing movements, the body of the parasite being at the same time agitated and jerked about. Finally, “ flagella ” (microgametes) may be suddenly projected from the periphery (Fig. 8, c , /), very much in the same way as they are

[CHAP.

projected from the periphery of the' crescent-derived sphere. Manifestly, these large spherical parasites and the flagellated bodies arising from some of them correspond to the crescent-derived sphere and crescent-derived flagellated body.

Conditions favouring and retarding eruption of microga metes, — By expos¬ ing the slide to the air with slight aqueous admixture, as by breathing on the slip before applying the cover-glass, it is generally easy to procure quickly, from crescent- containing blood, specimens of the flagellated body.

In certain bloods the flagellated body is easily procured ; in others the opposite is the case. As regards the crescents, doubtless success depends in a measure on the degree of maturity of the parasite, young or effete crescents failing to evolve. There are other conditions affecting the process, however, which are as yet unknown.

Double infection of red cells. — Occasion¬ ally, though rarely, sporulating and sexual forms of the malaria parasite may be seen inhabiting the same red corpuscle. The appear¬ ance thus produced is very puzzling, and gave rise to the theory put forward by Schaudinn that a process of “ parthenogenesis ” was apt to occur in the case of the malaria parasite, and that this would explain the “ latent stage ” of that organism. These bodies (Fig. 9) have been accurately described and figured by J. D. Thomson, and their nature is now perfectly clear. (See afso Plate I., B, 8.)

Mosquito-Malaria Theory

Popular and early views. — The idea that some relationship exists between the mosquito and malaria has long been enter¬ tained, not only by medical men but also by the inhabitants of malarial countries. This was a popular belief in Italy, as well as in East Africa. King and others many years ago pointed out how a mosquito-malarial hypothesis could best explain the epidemiological facts of malaria, but as to how the mosquito intervened they had no reasonable explanation to offer. Laveran, Koch, and Pfeiffer also expressed similar views. It remained for Manson first to offer a definite hypothesis.

A mosquito-malaria theory definitely formulated. — In

1894,* and again in 1896, Manson formulated a definite hypothesis

• Brit. Med. Joum.t December 8th, 181)4; “Goulstonian Lectures,” Brit . Med . Joum.t March 14th, 21st, and 28th, 189C.

Fig. 9. — Abnormal malaria parasites.

( After Dr. J. D.

Thomson, “ Jl.

R.A.M.C.")

1, Normal re<l corpuscle ; 2, gnmetocyte ami schizont ; 3, gametocyte and gametocyte ; 4, ganietocytc ami schizont; 5, schizont and schizont, both under* going schizogony.

il MOSQUITO-MALARIA THEORY 11

on the subject. Being a parasite, the germ of malaria, to keep in existence as a species, must pass from host to host ; in other words, must at some time have an extracorporeal life. From the fact that the flagellated body does not come into existence until the blood has left the blood-vessels — that is, until it is outside the body — he concluded that the function, then unknown, of the flagellum lay outside the human body, and that the flagellated body was the first phase of the extracorporeal life of the malaria parasite. As the parasite, whilst in the circulation, is always enclosed in a blood-corpuscle, and is therefore incapable of leaving the body by its own efforts, and as it is never, so far as is known, extruded in the excreta, he concluded that it is removed from the circulation by some blood-sucking animal, most probably by some suctorial insect common in the haunts of malaria. This blood-sucker he believed to be the mosquito, an insect whose habits seemed adapted for such a purpose, and whose distribution conformed to the well-ascer¬ tained habits of malaria. Further, basing his argument on what he had shown to be the fact in the case of Filaria barter of ti , and on the peculiarities of the distribution of malaria, he reasoned that only particular species of mosquito were capable of subserving particular species of malaria parasite.