Opening…

Preface

The English edition of Braun’s “Die Tierischen Parasiten des Menschen,” produced in 1906, being out of print, the publishers decided to issue another edition based on the translation of Braun’s fourth German edition, which appeared in 1908, to which had been added an appendix, by Dr. Otto Seifert on Treatment, etc.

When the work was considered with a view to a new edition, it was found that a vast amount of new matter had to be incorporated, numerous alterations essential for bringing it up to date were necessitated, and many omissions were inevitable. The result is that parts of the book have been rewritten, and, apart from early historical references, the work of Braun has disappeared. This is more particularly the case with the Protozoa section of the present work. The numerous additions, due to the great output of scientific literature and other delays in publication, have led to the book being somewhat less homogeneous than we desired, and have necessitated the use of appendices to allow of the presentation of new facts only recently ascertained. Many new illustrations have been added or substituted for older, less detailed ones. Some of these new figures were drawn specially for this book.

The first section, on the Protozoa, has been written by Dr. Fantham, there being little of the original text left except parts of the historical portions, and thus the section on Protozoa must be considered as new. The second section, on Worms (except the Acanthocephala, Gordiidæ and Hirudinea), has been remodelled by Professor Stephens to such an extent that this, too, must not be looked upon as a translation of Braun’s book. With regard to the Arthropoda, much remains as in the last English edition, but some new matter added by Braun in his fourth German edition is included, and much new matter by Mr. Theobald has been incorporated. As regards the Appendix by Dr. Seifert, the first section has been remodelled, but the sections on the Helminthes and the Arthropoda are practically translations of the original.

The authors desire to express their thanks to Miss A. Porter, D.Sc., J. P. Sharples, Esq., B.A., M.R.C.S., and H. F. Carter, Esq., F.E.S., for valuable help. They also wish to thank the authors, editors, and publishers of several manuals and journals for their courtesy in allowing the reproduction of certain of their illustrations. In this connection mention must be made more particularly of Professor Castellani, Dr. Chalmers, Professor Doflein, Dr. Leiper, the late Professor Minchin, Professor Nuttall, Dr. Wenyon, Mr. Edw. Arnold, Messrs. Baillière, Tindall and Cox, Messrs. Black, Messrs. Cassell, Dr. Gustav Fischer, Messrs. Heinemann, the Cambridge University Press, the Editors of the Annals of Tropical Medicine and Parasitology, the Editors of the Journal of Experimental Medicine, and the Editor of the Tropical Diseases Bulletin.

H. B. F. J. W. W. S. F. V. T.

December, 1915.

ERRATA xxxii

ON PARASITES IN GENERAL 1 Occasional and Permanent Parasitism 1 Entozoa, Endoparasites, Helminthes, Turbellaria 2 Hermaphroditism 4 Fertility of Parasites 5 Transmigrations 5 Commensals, Mutualists 6 Incidental and Pseudo-parasites 6 The Influence of Parasites on the Host 8 Origin of Parasites 10 Derivation of Parasites 19 Change of Host 20 Literature 22

THE ANIMAL PARASITES OF MAN 25 *A. Protozoa* 25

CLASSIFICATION OF THE PROTOZOA.

Class I. SARCODINA 27 Order. Amœbina 27 Foraminifera 27 Heliozoa 27 Radiolaria 28 Class II. MASTIGOPHORA 28 III. SPOROZOA 28 Sub-class 1. TELOSPORIDIA 28 Order. Gregarinida 28 Coccidiidea 28 Hæmosporidia 28 Sub-class 2. NEOSPORIDIA 28 Order. Myxosporidia 28 Microsporidia 28 Sarcosporidia 28 Haplosporidia 29 Class IV. INFUSORIA 29 V. SUCTORIA 29

Class I. SARCODINA, Bütschli, 1882 29 Order. Amœbina, Ehrenberg 29 A. Human Intestinal Amœbæ 29 Entamœba coli, Lösch, 1875, emend. Schaudinn, 1903 32 Entamœba histolytica, Schaudinn, 1903 34 Entamœba tetragena, Viereck, 1907 38 Noc’s Entamœba, 1909 41 Entamœba buccalis, Prowazek, 1904 43 Entamœba undulans, Castellani, 1905 43 Entamœba kartulisi, Doflein, 1901 44 Amœba gingivalis, A. buccalis, A. dentalis 44 Genus. Paramœba, Schaudinn, 1896 44 Paramœba (Craigia) hominis, Craig, 1906 45 B. Amœbæ from other Organs 45 Entamœba pulmonalis, Artault, 1898 45 Amœba urogenitalis, Baelz, 1883 45 Amœba miurai, Ijima, 1898 46 Appendix: “Rhizopods in Poliomyelitis Acuta” 46 Order. Foraminifera, d’Orbigny 47 Sub-order. Monothalamia (Testaceous Amœbæ) 47 Genus. Chlamydophrys, Cienkowski, 1876 47 Chlamydophrys enchelys, Ehrenberg 47 Leydenia gemmipara, Schaudinn, 1896 49

Class II. MASTIGOPHORA, Diesing 50 Sub-class. FLAGELLATA, Cohn emend. Bütschli 50 Order. Polymastigina, Blochmann 52 Genus. Trichomonas, Donné, 1837 52 Trichomonas vaginalis, Donné 52 Trichomonas intestinalis, R. Leuckart, 1879 = Trichomonas hominis, Davaine, 1854 54 Genus. Tetramitus, Perty, 1852 57 Tetramitus mesnili, Wenyon, 1910 57 Genus. Lamblia, R. Blanchard, 1888 57 Lamblia intestinalis, Lambl, 1859 57 Order. Protomonadina, Blochmann 60 Family. Cercomonadidæ, Kent emend. Bütschli 61 Genus. Cercomonas, Dujardin emend. Bütschli 61 Cercomonas hominis, Davaine, 1854 61 Monas pyophila, R. Blanchard, 1895 62 Family. Bodonidæ, Bütschli 63 Genus. Prowazekia, Hartmann and Chagas, 1910 63 Prowazekia urinaria, Hassall, 1859 63 Prowazekia asiatica, Castellani and Chalmers, 1910 65 Prowazekia javanensis, Flu, 1912 66 Prowazekia cruzi, Hartmann and Chagas, 1910 66 Prowazekia weinbergi, Mathis and Léger, 1910 66 Prowazekia parva, Nägler, 1910 66 Family. Trypanosomidæ, Doflein 66 Genus. Trypanosoma, Gruby, 1843 67 Historical 67 General 69 Morphology 70 Trypanosoma gambiense, Dutton, 1902 72 Trypanosoma nigeriense, Macfie, 1913 76 Trypanosoma rhodesiense, Stephens and Fantham, 1910 76 General Note on Trypanosomes with Posterior Nuclei 83 Trypanosoma cruzi, Chagas, 1909 83 Trypanosoma lewisi, Kent, 1881 88 Trypanosoma brucei, Plimmer and Bradford, 1899 93 Trypanosoma evansi, Steel, 1885 95 Trypanosoma equinum, Voges, 1901 96 Trypanosoma equiperdum, Doflein, 1901 97 Trypanosoma theileri, Bruce, 1902 98 Trypanosoma hippicum, Darling, 1910 98 Endotrypanum schaudinni, Mesnil and Brimont, 1908 99 Trypanosoma boylei, Lafont, 1912 99 Monomorphic Trypanosomes 99 Trypanosoma vivax, Ziemann, 1905 99 Trypanosoma capræ, Kleine, 1910 100 Trypanosoma congolense, Broden, 1904 100 Trypanosoma simiæ, Bruce, 1912 100 Trypanosoma uniforme, Bruce, 1910 101 General Note on Development of Trypanosomes in Glossina 101 Adaptation of Trypanosomes 101 Genus. Herpetomonas, Saville Kent, 1881 102 Genus. Crithidia, Léger, 1902, emend. Patton, 1908 104 Genus. Leishmania, Ross, 1903 104 Leishmania donovani, Laveran and Mesnil, 1903 105 Leishmania tropica, Wright, 1903 107 Leishmania infantum, Nicolle, 1908 109 Genus. Histoplasma, Darling, 1906 112 Genus. Toxoplasma, Nicolle and Manceaux, 1908 112

THE SPIROCHÆTES 114 The Spirochætes of the Blood 116 Spirochæta duttoni, Novy and Knapp, 1906 116 Spirochæta gallinarum, Stephens and Christophers, 1905 (= Spirochæta marchouxi, Nuttall, 1905) 119 Spirochæta recurrentis, Lebert, 1874 120 Spirochæta rossii, Nuttall, 1908 122 Spirochæta novyi, Schellack, 1907 122 Spirochæta carteri, Mackie and Manson, 1907 122 Spirochæta berbera, Sergent and Foley, 1910 122 Other Human Spirochætes 122 Some Animal Spirochætes 122

TREPONEMATA 124 Treponema pallidum, Schaudinn, 1905 124 Treponema pertenue, Castellani, 1905 127

Class III. SPOROZOA, Leuckart, 1879 128 Sub-class. TELOSPORIDIA, Schaudinn 129 Order. Gregarinida, Aimé Schneider emend. Doflein 129 Order. Coccidiidea 135 Genus. Eimeria, Aimé Schneider, 1875 142 Eimeria avium, Silvestrini and Rivolta 142 Eimeria stiedæ, Lindemann, 1865 145 (a) Human Hepatic Coccidiosis 148 (b) Human Intestinal Coccidiosis 148 (c) Doubtful Cases 149 Genus. Isospora, Aimé Schneider, 1881 149 Isospora bigemina, Stiles, 1891 149 Doubtful Species 150 Order. Hæmosporidia, Danilewsky emend. Schaudinn 151 The Malarial Parasites of Man 155 Development of the Malarial Parasites of Man 159 The Species of the Malarial Parasites of Man 164 Plasmodium vivax, Grassi and Feletti, 1890 164 Plasmodium malariæ, Laveran 166 Laverania malariæ, Grassi and Feletti, 1890 (= Plasmodium falciparum, Welch, 1897) 167 Plasmodium relictum, Sergent, 1907 (in birds) 170 Cultivation of Malarial Parasites 170 Differential Characters of the Human Malarial Parasites 171 Family. Piroplasmidæ, França, 1909 172 Genus. Babesia, Starcovici, 1893 174 Genus. Theileria, Bettencourt, França and Borges, 1907 178 Theileria parva, Theiler, 1903 178 Theileria mutans, Theiler, 1907 180 Genus. Anaplasma, Theiler, 1910 180 Genus. _Paraplasm_a, Seidelin, 1911 180 Sub-class. NEOSPORIDIA, Schaudinn 181 Order. Myxosporidia, Bütschli 181 Order. Microsporidia, Balbiani 184 Order. Actinomyxidia, Stolč. 187 Order. Sarcosporidia, Balbiani 187 Sarcosporidia observed in Man 193 Order. _Haplosporidi_a, Caullery and Mesnil, 1899 194 Rhinosporidium kinealyi, Minchin and Fantham, 1905 195

Class IV. INFUSORIA, Ledermüller, 1763 198 Genus. Balantidium, Claparède et Lachmann 200 Balantidium coli, Malmsten, 1857 200 Balantidium minutum, Schaudinn, 1899 204 Genus. Nyctotherus, Leidy, 1849 204 Nyctotherus faba, Schaudinn, 1899 205 Nyctotherus giganteus, P. Krause, 1906 205 [Nyctotherus] africanus, Castellani, 1905 206 THE CHLAMYDOZOA 207 PROTOZOA INCERTÆ SEDIS 210 Sergentella hominis, Brumpt, 1910 210

*B. Platyhelminthes (or Flat Worms)* 211

CLASSIFICATION OF THE PLATYHELMINTHES.

Class I. TURBELLARIA (or Eddy Worms) 212 Order 1. Rhabdocœlida 212 2. Tricladida 212 3. Polycladida 212 Class II. TREMATODA (Sucking Worms) 212 III. CESTODA (Tapeworms) 212

Class II. TREMATODA, Rud. 212 Development of the Trematodes 222 Biology 229

CLASSIFICATION OF THE TREMATODES OF MAN.

Order. Digenea, v. Beneden, 1858 230 Sub-order. Prostomata, Odhner, 1905 230 Group. Amphistomata, Rudolphi, 1801, ep., Nitzsch, 1819 230 Family. Paramphistomidæ, Fischoeder, 1901 231 Sub-family. Paramphistominæ, Fischoeder, 1901 231 Cladorchiinæ, Fischoeder, 1901 231 Family. Gastrodisciidæ, Stiles and Goldberger, 1910 231 Group. Distomata, Retzius, 1782 231 Family. Fasciolidæ, Railliet, 1895 231 Sub-family. Fasciolinæ, Odhner, 1910 231 Fasciolopsinæ, Odhner, 1910 231 Family. Opisthorchiidæ, Braun, 1901, emend, auctor. 232 Sub-family. Opisthorchiinæ, Looss, 1899, emend, auctor. 232 Metorchiinæ, Lühe, 1909 232 Family. Dicrocœliidæ, Odhner, 1910 232 Heterophyiidæ, Odhner, 1914 232 Troglotremidæ, Odhner, 1914 232 Echinostomidæ, Looss, 1902 233 Sub-family. Echinostominæ, Looss, 1899 233 Himasthlinæ, Odhner, 1910 233 Family. Schistosomidæ, Looss, 1899 233

THE TREMATODES OBSERVED IN MAN 234

Family. Paramphistomidæ, Stiles and Goldberger, emend. 1910 234 Sub-family. Cladorchiinæ, Fischoeder, 1901 234 Genus. Watsonius, Stiles and Goldberger, 1910 234 Watsonius watsoni, Stiles and Goldberger, 1910 234 Family. Gastrodisciidæ 236 Genus. Gastrodiscus, Lkt., 1877 236 Gastrodiscus hominis, Lewis and McConnell, 1876 236 Family. Fasciolidæ, Railliet, 1895 237 Sub-family. Fasciolinæ, Odhner, 1910 237 Genus. Fasciola, L., 1758 237 Fasciola hepatica, L., 1758 237 Halzoun 242 Fasciola gigantica, Cobbold, 1856 244 Sub-family. Fasciolopsinæ, Odhner, 1910 245 Genus. Fasciolopsis, Looss, 1898 245 Fasciolopsis buski, Lank., 1857 245 Fasciolopsis rathouisi, Ward, 1903 246 Fasciolopsis goddardi, Ward, 1910 247 Fasciolopsis fülleborni, Rodenwaldt, 1909 247 Family. Troglotremidæ, Odhner, 1914 249 Genus. Paragonimus, Braun, 1899 249 Paragonimus ringeri, Cobb., 1880 249 Family. Opisthorchiidæ, Braun, 1901 252 Sub-family. Opisthorchiinæ, Looss, 1899 252 Genus. Opisthorchis, R. Blanch., 1845 252 Opisthorchis felineus, Riv., 1885 252 Genus. Paropisthorchis, Stephens, 1912 255 Paropisthorchis caninus, Barker, 1912 255 Genus. Amphimerus, Barker, 1912 (?) 257 Amphimerus noverca, Barker, 1912 (?) 258 Genus. Clonorchis, Looss, 1907 258 Clonorchis sinensis, Cobbold, 1875 258 Clonorchis endemicus, Baelz, 1883 259 Sub-family. Metorchiinæ, Lühe, 1909 261 Genus. Metorchis, Looss, 1899, emend. auctor. 261 Metorchis truncatus, Rud., 1819 261 Family. Heterophyiidæ, Odhner, 1914 262 Genus. Heterophyes, Cobbold, 1866 262 Heterophyes heterophyes, v. Sieb., 1852 262 Metagonimus, Katsurada, 1913; Yokogawa, Leiper, 1913 264 Metagonimus yokogawai, Katsurada, 1913 264 Family. Dicrocœliidæ, Odhner, 1910 265 Genus. Dicrocœlium, Dujardin 265 Dicrocœlium dendriticum, Rud., 1819 266 Family. Echinostomidæ, Looss, 1902 267 Sub-family. Echinostominæ, Looss, 1899 267 Genus. Echinostoma, Rud., 1809; Dietz, 1910 267 Echinostoma ilocanum, Garrison, 1908 267 Echinostoma malayanum, Leiper, 1911 268 Sub-family. Himasthlinæ, Odhner, 1910 269 Genus. Artyfechinostomum, Clayton-Lane, 1915 269 Artyfechinostomum sufrartyfex, Clayton-Lane, 1915 269 Family. Schistosomidæ, Looss, 1899 269 Genus. Schistosoma, Weinl., 1858 269 Schistosoma hæmatobium, Bilharz, 1852 270 Schistosoma mansoni, Sambon, 1907 277 Schistosoma japonicum, Katsurada, 1904 277

Class III. CESTODA, Rud., 1808 282 Anatomy of the Cestoda 284 Development of the Tapeworms 297 Biology 306

CLASSIFICATION OF THE CESTODA OF MAN.

Order. Pseudophyllidea, Carus, 1863 308 Family. Dibothriocephalidæ, Lühe, 1902 308 Sub-family. Dibothriocephalinæ, Lühe, 1899 308 Order. Cyclophyllidea, v. Beneden 308 Family. Dipylidiidæ, Lühe, 1910 309 Hymenolepididæ, Railliet and Henry, 1909 309 Davaineidæ, Fuhrmann, 1907 309 Sub-family. Davaineinæ, Braun, 1900 309 Family. Tæniidæ, Ludwig, 1886 309

THE CESTODES OF MAN 309 Family. Dibothriocephalidæ 309 Sub-family. Dibothriocephalinæ 309 Genus. Dibothriocephalus, Lühe, 1899 309 Dibothriocephalus latus, L., 1748 310 Dibothriocephalus cordatus, R. Lkt., 1863 315 Dibothriocephalus parvus, Stephens, 1908 316 Genus. Diplogonoporus, Lönnbrg., 1892 316 Diplogonoporus grandis, R. Blanch., 1894 316 Sparganum, Diesing, 1854 317 Sparganum mansoni, Cobb., 1883 317 Sparganum proliferum, Ijima, 1905 318 Family. Dipylidiidæ, Lühe, 1910 320 Genus. Dipylidium, R. Lkt., 1863 320 Dipylidium caninum, L. 1758 320 Family. Hymenolepididæ, Railliet and Henry, 1909 323 Genus. Hymenolepis, Weinland, 1858 323 Hymenolepis nana, v. Sieb., 1852 323 Hymenolepis diminuta, Rud., 1819 326 Hymenolepis lanceolata, Bloch, 1782 328 Family. Davaineidæ, Fuhrmann, 1907 329 Sub-family. Davaineinæ, Braun, 1900 329 Genus. Davainea, R. Blanch., 1891 329 Davainea madagascariensis, Davaine, 1869 329 Davainea (?) asiatica, v. Linst., 1901 330 Family. Tæniidæ, Ludwig, 1886 331 Genus. Tænia, L., 1758 331 Tænia solium, L., p. p., 1767 331 Cysticercus acanthotrias, Weinland, 1858 336 Tænia bremneri, Stephens, 1908 337 Tænia marginata, Batsch., 1786 338 Tænia serrata, Goeze, 1782 338 Tænia crassicollis, Rud., 1810 338 Tænia saginata, Goeze, 1782 338 Tænia africana, v. Linst., 1900 342 Tænia confusa, Ward, 1896 343 Tænia echinococcus, v. Sieb., 1853 344 Structure and Development of Echinococcus(Hydatid) 347 Echinococcus multilocularis (Alveolar Colloid) 356 Serum Diagnosis of Echinococcus 359

*C. Nemathelminthes* 360 Class. NEMATODA 360 Anatomy of the Nematodes 360 Development of the Nematodes 371

CLASSIFICATION OF THE NEMATODA.

Family. Anguillulidæ, Gervais and van Beneden, 1859 374 Angiostomidæ, Braun, 1895 374 Gnathostomidæ 374 Dracunculidæ, Leiper, 1912 374 Filariidæ, Claus, 1885 374 Trichinellidæ, Stiles and Crane, 1910 375 Dioctophymidæ 375 Strongylidæ, Cobbold, 1864 375 Physalopteridæ 375 Ascaridæ, Cobbold, 1864 375 Oxyuridæ 375

THE NEMATODES OBSERVED IN MAN 376 Family. Anguillulidæ 377 Genus. Rhabditis, Dujardin, 1845 377 Rhabditis pellio, Schneider, 1866 377 Rhabditis niellyi, Blanchard, 1885 378 Rhabditis, sp. 378 Genus. Anguillula, Ehrenberg, 1826 379 Anguillula aceti, Müller, 1783 379 Genus. Anguillulina, Gervais and Beneden, 1859 379 Anguillulina putrefaciens, Kühn, 1879 379 Family. Angiostomidæ, Braun, 1895 379 Genus. Strongyloides, Grassi, 1879 379 Strongyloides stercoralis, Bavay, 1877 380 Family. Gnathostomidæ 384 Genus. Gnathostoma, Owen, 1836 384 Gnathostoma siamense, Levinson, 1889 384 Gnathostoma spinigerum, Owen, 1836 385 Family. Dracunculidæ, Leiper, 1912 385 Genus. Dracunculus, Kniphoff, 1759 385 Dracunculus medinensis, Velsch, 1674 386 Genus (of Crustacea). Cyclops, Müller, 1776 390 Family. Filariidæ 390 Sub-family. Filariinæ 390 Genus. Filaria, O. Fr. Müller, 1787 390 Filaria bancrofti, Cobbold, 1877 390 Filaria demarquayi, Manson, 1895 403 Filaria taniguchi, Penel, 1905 404 Filaria (?) conjunctivæ, Addario, 1885 404 Group. Agamofilaria, Stiles, 1906 406 Agamofilaria georgiana 406 Agamofilaria palpebralis, Pace, 1867 (nec Wilson, 1844) 406 Agamofilaria oculi humani, v. Nordmann, 1832 406 Agamofilaria labialis, Pane, 1864 407 Filaria (?) romanorum-orientalis, Sarcani, 1888 407 Filaria (?) kilimaræ, Kolb, 1898 407 Filaria (?) sp. ? 407 Genus. Setaria, Viborg, 1795 407 Setaria equina, Abildg., 1789 408 Genus. Loa, Stiles, 1905 409 Loa loa, Guyot, 1778 409 Genus. Acanthocheilonema, Cobbold, 1870 414 Acanthocheilonema perstans, Manson, 1891 414 Genus. Dirofilaria, Railliet and Henry, 1911 416 Dirofilaria magalhãesi, R. Blanchard, 1895 417 Sub-family. Onchocercinæ, Leiper, 1911 417 Genus. Onchocerca, Diesing, 1841 417 Onchocerca volvulus, R. Leuckart, 1893 417 Family. Trichinellidæ, Stiles and Crane, 1910 419 Sub-family. Trichurinæ, Ransom, 1911 419 Genus. Trichuris, Röderer and Wagler, 1761 419 Trichuris trichiura, Linnæus, 1761 419 Sub-family. Trichinellinæ, Ransom, 1911 421 Genus. Trichinella, Railliet, 1895 421 Trichinella spiralis, Owen, 1835 421 History of the Development of Trichinella spiralis 423 Family. Dioctophymidæ 431 Genus. Dioctophyme, Collet-Megret, 1802 431 Dioctophyme gigas, Rudolphi, 1802 431 Family. Strongylidæ 432 Sub-family. Metastrongylinæ, Leiper, 1908 432 Genus. Metastrongylus, Molin, 1861 432 Metastrongylus apri, Gmelin, 1789 432 Sub-family. Trichostrongylinæ, Leiper, 1908 433 Genus. Trichostrongylus, Looss, 1905 434 Trichostrongylus instabilis, Railliet, 1893 434 Trichostrongylus probolurus, Railliet, 1896 435 Trichostrongylus vitrinus, Looss, 1905 435 Genus. Hæmonchus, Cobb., 1898 436 Hæmonchus contortus, Rudolphi, 1803; Cobb., 1898 436 Genus. Nematodirus, Ransom, 1907, emend. Railliet, 1912 438 Sub-genus. Mecistocirrus, Railliet, 1912 438 Mecistocirrus fordi, Daniels, 1908 438 Sub-family. Ancylostominæ, Railliet, 1909 438 Group. Œsophagostomeæ, Railliet and Henry, 1909 439 Genus. Ternidens, Railliet, 1909 439 Ternidens deminutus, Railliet and Henry, 1905 440 Genus. Œsophagostomum, Molin, 1861 441 Œsophagostomum brumpti, Railliet and Henry, 1905 441 Œsophagostomum stephanostomum var. thomasi, Railliet and Henry, 1909 443 Œsophagostomum apiostomum, Willach, 1891 444 Group. Ancylostomeæ, Railliet and Henry, 1909 445 Genus. Ancylostoma, Dubini, 1843, emend. Looss, 1905 445 Ancylostoma duodenale, Dubini, 1843 445 Ancylostoma ceylanicum, Looss, 1911 456 Ancylostoma braziliense, Gomez de Faria, 1910 456 Group. Bunostomeæ, Railliet and Henry, 1909 456 Genus. Necator, Stiles, 1903 457 Necator americanus, Stiles, 1902 457 Necator exilidens, Cummins, 1912 459 Ancylostomiasis 459 Group. Syngameæ, Railliet and Henry, 1909 459 Genus. Syngamus, von Siebold, 1836 459 Syngamus kingi, Leiper, 1913 459 Family. Physalopteridæ 460 Genus. Physaloptera, Rudolphi, 1819 460 Physaloptera caucasica, v. Linstow, 1902 461 Physaloptera mordens, Leiper, 1907 461 Family. Ascaridæ, Cobbold, 1864 461 Sub-family. Ascarinæ 461 Genus. Ascaris, L., 1758 461 Ascaris lumbricoides, L., 1758 463 Ascaris sp. 465 Ascaris texana, Smith et Goeth, 1914 465 Ascaris maritima, Leuckart, 1876 465 Genus. Toxascaris, Leiper, 1907 465 Toxascaris limbata, Railliet and Henry, 1911 466 Genus. Belascaris, Leiper, 1907 466 Belascaris cati, Schrank, 1788 466 Belascaris marginata, Rudolphi, 1802 466 Genus. Lagocheilascaris, Leiper, 1909 466 Lagocheilascaris minor, Leiper, 1909 467 Family. Oxyuridæ 467 Genus. Oxyuris, Rudolphi, 1803 467 Oxyuris vermicularis, Linnæus, 1767 467 Family. Mermithidæ 469 Genus. Mermis, Dujardin, 1845 469 Mermis hominis oris, Leidy, 1850 469 Agamomermis, Stiles, 1903 470 Agamomermis restiformis, Leidy, 1880 470 TECHNIQUE 471

*D. Acanthocephala*, Rud 475 Echinorhynchus gigas, Goeze, 1782 477 Echinorhynchus hominis, Lambl, 1859 478 Echinorhynchus moniliformis, Bremser, 1819 478

*E. Gordiidæ* 479

*F. Hirudinea s. Discophora* (Leech) 480 Family. Gnathobdellidæ (Leeches with Jaws) 481 Genus. Hirudo, L., 1758 481 Hirudo medicinalis, L., 1758 481 Hirudo troctina, Johnston, 1816 482 Genus. Limnatis, Moq.-Tandon, 1826 482 Limnatis nilotica, Savigny, 1820 482 Genus. Hæmadipsa, Tennent, 1861 482 Family. Rhynchobdellidæ (Leeches with Rostrum) 482 Genus. Hæmentaria, de Filippi, 1849 482 Hæmentaria officinalis, de Filippi 482 Genus. Placobdella, R. Blanchard 482 Placobdella catenigera, Moq.-Tandon 482

*G. Arthropoda* (Jointed-limbed Animals) 483 A. ARACHNOIDEA (Spiders, Mites, etc.) 483 Order. Acarina (Mites) 484 Family. Trombidiidæ (Running Mites) 485 Genus. Trombidium, Latreille (and Leptus) 485 Leptus autumnalis, Shaw, 1790 485 Trombidium tlalsahuate, Lemaire, 1867 486 Akamushi or Kedani 487 Family. Tetranychidæ (Spinning Mites) 488 Genus. Tetranychus, Dufour 488 Tetranychus molestissimus, Weyenbergh, 1886 488 Tetranychus telarius, L., 1758, var. russeolus, Koch 488 Family. Tarsonemidæ 488 Genus. Pediculoides 489 Pediculoides ventricosus, Newport, 1850 489 Genus. Nephrophages 490 Nephrophages sanguinarius, Miyake and Scriba, 1893 490 Family. Eupodidæ 491 Genus. Tydeus, Koch 491 Tydeus molestus, Moniez, 1889 491 Family. Gamasidæ (Coleopterous or Insect Mites) 491 Genus. Dermanyssus, Dugès 492 Dermanyssus gallinæ, de Geer, 1778 492 Dermanyssus hirundinis, Hermann, 1804 492 Genus. Holothyrus 493 Holothyrus coccinella, Gervais, 1842 493 Family. Ixodidæ (Ticks) 493 Classification of Ixodidæ 496 Synopsis of Genera 496 Genus. Ixodes, Latreille 497 Ixodes reduvius, L., 1758 497 Ixodes holocyclus, Neumann, 1899 499 Ixodes hexagonus, Leach, 1815 500 Genus. Amblyomma, Koch 500 Amblyomma cayennense, Koch, 1844 500 Amblyomma americana, Linnæus 501 Amblyomma maculatum, Koch 501 Genus. Hyalomma, Koch 501 Hyalomma ægyptium, L., 1758 501 Genus. Hæmaphysalis, Koch 502 Hæmaphysalis punctata, Canestrini and Fanzago, 1877–1878 502 Genus. Dermacentor, Koch 502 Dermacentor reticulatus, Fabricius, 1794 502 Dermacentor venustus, Banks 503 Dermacentor occidentalis, Neumann 504 Dermacentor variabilis, Say 505 Genus. Margaropus, Karsch 505 Margaropus annulatus australis, Fuller 505 Margaropus microplus, Canestrini 505 Genus. Rhipicephalus, Koch 505 Rhipicephalus sanguineus, Latreille, 1804 505 Neumann’s Table of Species of Argas 505 Genus. Argas, Latreille 506 Argas reflexus, Fabricius, 1794 506 Argas persicus, Fischer de Waldheim, 1824 506 Argas brumpti, Neumann 507 Argas chinche, Gervais, 1844 508 Genus. Ornithodorus, Koch 508 Ornithodorus moubata, Murray, 1877 508 Ornithodorus savignyi, Audouin, 1827 509 Ornithodorus coriaceus, Koch 509 Ornithodorus talaje, Guerin, 1849 509 Ornithodorus turicata, Dugès, 1876 509 Ornithodorus tholozani, Laboulbène and Mégnin, 1882 510 Ornithodorus mégnini, Dugès, 1883 510 Family. Tyroglyphidæ 511 Sub-family. Tyroglyphinæ 511 Genus. Aleurobius, Canestrini 511 Aleurobius (Tyroglyphus) farinæ, de Geer (part), Koch 511 Genus. Tyroglyphus, Latreille 511 Tyroglyphus siro, L., 1756 511 Tyroglyphus longior, Gervais, 1844 512 Tyroglyphus minor var. castellani, Hirst 513 Genus. Glyciphagus, Hering, 1838 513 Glyciphagus prunorum, Hering, and G. domesticus, de Geer 513 Glyciphagus cursor, Gervais 513 Glyciphagus buski, Murray 513 Genus. Rhizoglyphus, Claparède, 1869 514 Rhizoglyphus parasiticus, Dalgetty, 1901 514 Genus. Histiogaster, Berlese, 1883 515 Histiogaster (entomophagus ?) spermaticus, Trouessart, 1900 515 Genus. Cheyletus 516 Cheyletus mericourti, Lab. 516 Family. Sarcoptidæ (Itch Mites) 516 Sub-family. Sarcoptinæ 518 Genus. Sarcoptes, Latreille 518 Sarcoptes scabiei, de Geer, 1778 518 Sarcoptes minor, Fürstenberg, 1861 520 Family. Demodicidæ (Mites of the Hair-follicles) 522 Genus. Demodex, Owen 522 Demodex folliculorum, Simon, 1842 522 Order. Pentastomida 523 Family. Linguatulidæ 523 Genus. Linguatula, Fröhlich_ 524 Linguatula rhinaria, Pilger, 1802 524 Genus. Porocephalus 526 Porocephalus constrictus, v. Siebold, 1852 526

B. INSECTA (Hexapoda) 529

CLASSIFICATION OF THE HEXAPODA.

(1) Aptera 531 (2) Neuroptera 531 (3) Orthoptera 531 (4) Thysanoptera 531 (5) Hemiptera 531 (6) Diptera 532 (7) Lepidoptera 532 (8) Hymenoptera 532 (9) Coleoptera 532 Order. Rhyncota 532 (a) Rhyncota aptera parasitica 532 Family. Pediculidæ (Lice) 532 Genus. Pediculus, Linnæus 532 Pediculus capitis, de Geer, 1778 532 Pediculus vestimenti, Nitzsch, 1818 533 Genus. Phthirius, Leach 534 Phthirius inguinalis, Redi, 1668 534 (b) Rhyncota hemiptera 534 Family. Acanthiadæ 534 Genus. Cimex , Linnæus 534 Cimex lectularius , Linnæus 534 Cimex rotundatus, Signoret, 1852 536 Cimex columbarius, Jenyns 536 Cimex ciliatus, Eversmann, 1841 537 Family. Reduviidæ 537 Genus. Conorhinus, Lap. 537 Conorhinus megistus, Burm. 537 Conorhinus sanguisuga, Lec. (Blood-sucking Cone-nose) 537 Conorhinus, sp. novum (Monster Bug) 538 Conorhinus rubrofasciatus, de Geer (Malay Bug) 538 Conorhinus renggeri, Herr-Schäff (Great Black Bug of Pampas) 539 Conorhinus variegatus (Variegated Cone-nose) 539 Conorhinus nigrovarius 539 Conorhinus protractus 539 Genus. Reduvius, etc. 539 Reduvius personatus, Linné 539 Coriscus subcoleoptratus, Kirby, 1837 540 Rasahus biguttatus, Say, 1831 540 Melanolestes morio, Erichson, 1848 (non-Walker) 540 Melanolestes abdominalis, Herrich-Schäffer, 1848 540 Phonergates bicoloripes 541 Family. Aradidæ 541 Dysodius lunatus, Fabr. (Pito Bug) 541 The Ochindundu 541 Family. Lygæidæ 541 Lyctocoris campestris, Fabricius 541 Rhodinus prolixus, Stål, 1859 541 Order. Orthoptera 542 Locusts Injurious to Man 542 Order. Coleoptera 542 Silvanus surinamensis, Linnæus (Saw-toothed Grain Beetle) 542 Order. Diptera 543 Aphaniptera or Siphonaptera (Fleas) 543 Family. Sarcopsyllidæ (Jiggers) 543 Genus. Dermatophilus, Guérin 544 Dermatophilus cæcata, Enderl. 544 Dermatophilus penetrans, L., 1758 (Jigger, Chigoe) 544 Genus. Echidnophaga, Olliff 544 Echidnophaga gallinacea, Westwood (Chigoe of Fowls) 544 Family. Pulicidæ (True Fleas) 545 Genus. Pulex, Linn. 545 Pulex irritans, L., 1758 545 Genus. Xenopsylla, Glink 546 Xenopsylla cheopis, Rothschild 546 Xenopsylla brasiliensis, Baker 547 Genus. Ctenocephalus, Kolenati 547 Genus. Hoplopsyllus, Baker 547 Hoplopsyllus anomalus, Baker 547 Genus. Ceratophyllus, Centis 547 Ceratophyllus fasciatus, Bosc 547 Genus. Ctenopsylla, Kolenati 548 Genus. Hystrichopsylla, Taschenberg 548 Pulex pallipes 548 SYSTEMATIC ANATOMICAL AND BIOLOGICAL REMARKS ON MOSQUITOES 548 CULICIDÆ OR MOSQUITOES 555 The Classification of Culicidæ 561 Notes on the Different Genera 566 Sub-family. Anophelina 566 Genus. Anopheles, Meigen 566 Genus. Myzomyia, Blanchard; Grassia, Theobald 567 Genus. Neomyzomyia, Theobald 567 Genus. Cycloleppteron, Theobald 567 Genus. Feltinella, Theobald 567 Genus. Stethomyia, Theobald 567 Genus. Pyretophorus, Blanchard; Howardia, Theobald 567 Genus. Myzorhynchella, Theobald 568 Genus. Manguinhosia, Cruz (in Peryassu) 568 Genus. Chrystya, Theobald 568 Genus. Lophoscelomyia, Theobald 568 Genus. Arribalzagia, Theobald 568 Genus. Myzorhynchus, Blanchard; Rossia, Theobald 568 Genus. Nyssorhynchus, Blanchard; Laverania, Theobald 569 Genus. Cellia, Theobald 569 Genus. Neocellia, Theobald 569 Genus. Kertészia, Theobald 569 Genus. Manguinhosia, Cruz 569 Genus. Chagasia, Cruz 570 Genus. Calvertina, Ludlow 570 Genus. Birónella, Theobald 570 Sub-family. Megarhininæ 570 Genus. Megarhinus, Robineau Desvoidy 570 Genus. Toxorhynchites, Theobald 570 Sub-family. Culicinæ 571 Genus. Mucidus, Theobald 571 Genus. Psorophora, Robineau Desvoidy 571 Genus. Janthinosoma, Arribalzaga 571 Genus. Stegomyia, Theobald 571 Stegomyia fasciata, Fabricius (Yellow Fever Mosquito) 574 Stegomyia scutellaris, Walker 575 Genus. Theobaldia, Neveu-Lemaire 575 Theobaldinella, Blanchard 575 Theobaldia annulata, Meigen 575 Genus. Culex, Linnæus 575 Genus. Melanoconion, Theobald 576 Genus. Grabhamia, Theobald 576 Genus. Pseudotæniorhynchus, Theobald; Tæniorhynchus, Theobald, non-Arribalzaga 576 Genus. Tæniorhynchus, Arribalzaga; Mansonia, Blanchard; Panoplites, Theobald 577 Genus. Chrysoconops, Goeldi 577 Other Nematocera 577 Family. Simulidæ 577 Family. Chironomidæ (Midges) 579 Sub-family. Ceratopogoninæ 580 Family. Psychodidæ (Owl Midges) 581 Brachycera (Flies) 582 Family. Phoridæ 582 Aphiochæta ferruginea, Brun 583 Phora rufipes, Meig. 583 Family. Sepsidæ 583 Piophila casei, L. 583 Family. Syrphidæ (Hover and Drone Flies) 583 Family. Drosophilidæ 584 Drosophila melanogaster, Br. 584 Family. Muscidæ 584 Teichomyza fusca, Macq. 584 Homalomyia canicularis, L., etc. 584 Homalomyia scalaris, Fabr. 585 Anthomyra desjardensii, Macq. 585 Hydrotæa meteorica, L. 585 Cyrtoneura stabulans 585 Musca domestica, Linn. (Common House-fly) 585 Genus. Chrysomyia, Rob. Desv. 587 Chrysomyia (Compsomyia) macellaria, Fabr.; Lucilia macellaria, Fabr. 587 Chrysomyia viridula, Rob. Desv. 588 Genus. Lucilia, Rob. Desv. 588 Lucilia nobilis, Meig. 588 Genus. Pycnosoma, Brauer and v. Bergenstamm 588 Genus. Sarcophaga, Mg. 589 Sarcophaga carnaria, L., 1758 589 Sarcophaga magnifica, Schiner, 1862 589 Sarcophaga chrysotoma, Wied 590 Sarcophaga plinthopyga, Wied 590 Ochromyia anthropophaga, E. Blanch.; Cordylobia arthrophaga,Grünberg 590 Auchmeromyia (Bengalia) depressa (Walker) 591 Genus. Cordylobia, Grünberg, 1903 591 Cordylobia grünbergi, Dönitz 591 Cordylobia anthropophaga, Grünberg 592 Lund’s Larva 593 Auchmeromyia luteola, Fabricius 593 Family. Oestridæ 594 Cutaneous Oestridæ 595 Genus. Hypoderma, Latreille 595 Hypoderma bovis, de Geer 595 Hypoderma lineata, de Villers 596 Hypoderma diana, Brauer 596 Genus. Dermatobia, Brauer 596 Dermatobia cyaniventris, Macq. 596 Cavicolous Oestridæ 598 Genus. Oestrus, Linnæus 598 Oestrus (Cephalomyia) ovis, L. 598 Gastricolous Oestridæ 599 Genus. Gastrophilus, Leach 599 Biting-mouthed and other Noxious Diptera which may be Disease Carriers 600 Family. Tabanidæ (Gad Flies) 600 Family. Asilidæ (Wolf Flies) 602 Family. Leptidæ 603 Blood-sucking Muscidæ 603 Genus. Glossina, Westwood 603 Glossina palpalis, Rob. Desv. 607 Glossina morsitans, Westwood 608 Genus. Stomoxys, Geoffroy 609 Genus. Lyperosia, Rondani 610 Pupipara or Eproboscidæ 611 Insects and Epidemic Poliomyelitis 612

ADDENDA 613 Akamushi or Kedani Sickness 613 Ticks.--African Tick Fever 613 Tick Paralysis 613 Diptera.--Psychodidæ 613 Pulicidæ.--Dermatophilus (Sarcopsylla) penetrans, or the “Jigger” 613 Brachycera.--Leptidæ 613 Myiasis 615 Auricular Myiasis 615 Body, Head, and Clothes Lice 615

SUPPLEMENT: CLINICAL AND THERAPEUTICAL NOTES 617 *Protozoa* 617 Introduction 617 I.--AMŒBIC DYSENTERY 618 II.--TRYPANOSOMIASES 620 African Sleeping Sickness 620 South American Trypanosomiasis 623 III.--FLAGELLATE DIARRHŒA AND DYSENTERY 623 IV.--LEISHMANIASES 626 A. Kala-azar 626 Indian 626 Infantile 627 B. Oriental Sore, due to Leishmania tropica 627 Naso-oral (Espundia) 628 V.--SPIROCHÆTOSES 629 A. Relapsing Fevers 629 B. Yaws or Frambœsia tropica 632 C. Syphilis 632 D. Bronchial Spirochætosis 632 VI.--MALARIA 633 VII.--BALANTIDIAN DYSENTERY 637 *Plathelminthes* (Flat Worms) 638 FASCIOLIASIS 638 Fasciola hepatica 638 Fasciolopsis buski 638 PARAGONIMIASIS 639 Paragonimus ringeri 639 Clonorchis sinensis 640 BILHARZIASIS 641 Schistosoma hæmatobium 641 CESTODES 644 General 644 Dibothriocephalus latus 658 Sparganum mansoni 659 Dipylidium caninum (Tænia cucumerina) 659 Hymenolepis nana 661 Tænia solium 662 Tænia saginata 667 NEMATODES 674 Strongyloides stercoralis 674 Dracunculus medinensis (Dracontiasis) 675 Filaria bancrofti 676 Loa loa 678 Trichuris trichiura 678 Trichinella spiralis 680 Eustrongylus gigas 681 Ancylostoma duodenale (Ancylostomiasis) 682 Ascaris lumbricoides (Ascariasis) 687 Oxyuris vermicularis (Oxyuriasis) 694 *Hirudinea* (Leeches) 699 *Arthropoda* 702 ARACHNOIDEA 702 Leptus autumnalis (Grass, Harvest, or Gooseberry Mite) 702 Kedani, Akaneesch (The Japanese River or Inundation Disease) 703 Dermanyssus gallinæ (avium) 703 Ixodes reduvius (ricinus ) 704 Sarcoptes scabiei (Scabies) 704 Demodex folliculorum 708 Demodex folliculorum canis 709 INSECTA 709 Pediculus capitis (Head Louse) 709 Pediculus vestimenti (Clothes Louse) 710 Phthirius inguinalis (Pediculus pubis) (Crab Louse) 711 Cimex (Acanthia) lectularia (Cimex lectularius) (Bed Bug) 713 Pulex irritans (Human Flea) 714 Dermatophilus (Sarcopsylla) penetrans (Sand Flea) 714 Myiasis 715 Myiasis externa 715 Gastricolous Oestridæ (Creeping Disease) 729

APPENDIX ON PROTOZOOLOGY 733 I.--NOTES ON RECENT RESEARCHES 733 Differences between Entamœba histolytica and E. coli 733 Phagedænic Amœbæ 733 Endamœba gingivalis 733 Entamœba kartulisi 734 Craigia and Craigiasis 734 Human Trichomoniasis 734 Chilomastix (Tetramitus) mesnili 735 Giardia (Lamblia) intestinalis 736 Cercomonas hominis 736 Transmissive Phase of Trypanosomes in Vertebrates 737 Trypanosoma lewisi 737 Blepharoplastless Trypanosomes 737 The Experimental Introduction of certain Insect Flagellates into various Vertebrates, and its bearing on the Evolution of Leishmaniasis 737 The Transmission of Spirochæta duttoni 739 Spirochæta bronchialis 739 The Spirochætes of the Human Mouth 740 Coccidia in Cattle 741 The Hæmosporidia 742 The Leucocytozoa of Birds 742

II.--FORMULÆ OF SOME CULTURE MEDIA 742 Culture Media for growing Amœbæ 742 Culture Media for the growth of Protozoa parasitic in the Blood 744

III.--BRIEF NOTES ON GENERAL PROTOZOOLOGICAL TECHNIQUE 745 Fresh Material 745 Stained Material 747 Fixatives 748 Stains 749

APPENDIX ON TREMATODA AND NEMATODA 753 TREMATODA 753 Artyfechinostomum sufrartyfex 753 Metagonimus (Yokogawa) yokogawai 753 Opisthorchis sp. 753 Schistosome cercariæ 753 Distomata cercariæ 753 Group. Ferrocercous cercariæ 753 Family. Schistosomidæ 753 Cercaria bilharzia, Leiper, 1915 754 Cercaria bilharziella, Leiper, 1915 754 Schistosoma mansoni, Sambon, 1907 754 NEMATODA 754 Ancylostomiasis 754 Ground Itch 754 Ascaris lumbricoides 754 Filariasis 755 Onchocerca volvulus 755 Strongyloides stercoralis 755

BIBLIOGRAPHY 756 INDEX 836

LIST OF ILLUSTRATIONS.

FIG. PAGE

1 Amœba coli. (After Loesch) 29 2 Encysted intestinal amœbæ. (After Grassi) 31 3 Entamœba coli, life-cycle. (After Castellani and Chalmers) 32 4 Entamœba coli, so-called autogamy. (From Minchin) 34 5 Entamœba histolytica (tetragena form). (After Hartmann) 35 6 Entamœba histolytica, ingestion of red blood corpuscles. (After Hartmann) 35 7 Entamœba histolytica, section through infected intestinal ulcer. (After Harris) 36 8 Entamœba histolytica (tetragena), trophozoite and nuclei. (After Hartmann) 38 9 Entamœba histolytica (tetragena), cysts. (After Hartmann) 39 10 Entamœba buccalis. (After Leyden and Löwenthal) 43 11 Entamœba kartulisi. (After Kartulis) 44 12 Amœba miurai. (After Ijima) 46 13 Chlamydophrys enchelys. (After Cienkowski) 48 14 Chlamydophrys enchelys, encysted. (After Cienkowski) 49 15 Leydenia gemmipara, Schaudinn 50 16 Trichomonas vaginalis. (After Künstler) 53 17 Trichomonas intestinalis. (After Grassi) 54 18 Trichomonas intestinalis. (Original, Fantham) 55 19 Lamblia intestinalis. (After Wenyon, from Minchin) 58 20 Lamblia intestinalis. (After Grassi and Schewiakoff) 59 21 Cercomonas hominis. (After Davaine) 61 22 Cercomonas hominis, from an echinococcus cyst. (After Lambl) 61 23 Monas pyophila. (After Grimm) 62 24 Prowazekia urinaria. (After Sinton) 64 25 Prowazekia urinaria, excystation. (After Sinton) 65 26 Trypanosoma brucei in division. (After Laveran and Mesnil) 70 27 Trypanosoma lewisi, rosettes. (After Laveran and Mesnil) 71 28 Trypanosoma gambiense. (After Dutton) 73 29 Trypanosoma gambiense, development in vertebrate host. (Original, Fantham) 73 30 Trypanosoma gambiense, development in Glossina palpalis. (After Robertson) 75 31 Trypanosoma rhodesiense. (After Stephens and Fantham) 77 32 Chart showing daily counts of number of Trypanosomes per cubic millimetre of peripheral blood from a case of Rhodesian sleeping sickness. (After Ross and Thomson) 79 33 Trypanosoma cruzi, schizogony. (After Chagas, from Castellani and Chalmers) 84 34 Trypanosoma cruzi in muscle. (After Vianna, from Castellani and Chalmers) 85 35 Trypanosoma cruzi, development in Triatoma megista. (After Chagas, from Castellani and Chalmers) 86 36 Trypanosoma cruzi, forms found in salivary glands of Triatoma. (After Chagas, from Castellani and Chalmers) 87 37 Trypanosoma lewisi, from rat’s blood. (After Minchin) 89 38 Trypanosoma lewisi, from stomach of rat-flea. (After Minchin) 91 39 Trypanosoma lewisi, from rectum of rat-flea. (After Minchin) 92 40 Trypanosoma brucei. (After Laveran and Mesnil) 94 41 Trypanosoma evansi. (Original, Fantham) 96 42 Trypanosoma equinum. (After Laveran and Mesnil) 96 43 Trypanosoma equiperdum. (Original, Fantham) 97 44 Trypanosoma theileri. (After Laveran and Mesnil) 98 45 Trypanosoma vivax. (Original, Fantham) 100 46 Trypanosoma congolense. (Original, Fantham) 100 47 Trypanosoma uniforme. (Original, Fantham) 100 48 Trypanosoma rotatorium. (After Laveran and Mesnil) 101 49 Herpetomonas, Crithidia, Trypanosoma. (After Porter) 103 50 Leishmania donovani. (After Christophers, Patton, Leishman; from Castellani and Chalmers) 106 51 Toxoplasma gondii. (After Laveran and Marullaz, from Trop. Dis. Bulletin) 113 52 Toxoplasma pyrogenes. (After Castellani, from Trop. Dis. Bulletin) 113 53 Spirochæta balbianii. (After Fantham and Porter) 114 54 Spirochæta duttoni. (After Fantham) 117 55 Spirochæta duttoni and its coccoid bodies in the tick. (After Fantham) 118 56 Treponema pallidum. (After Bell, from Castellani and Chalmers) 124 57 Treponema pallidum, apparatus for cultivation of. (After Noguchi) 125 58 Treponema pertenue. (After Castellani and Chalmers) 127 59 Monocystis agilis. (After Stein) 130 60 Gregarina longa, stages of growth of trophozoite 130 61 Xyphorhynchus firmus. (After Léger) 131 62 Gregarina munieri. (After Schewiakoff) 131 63 Monocystis agilis, spores. (After Bütschli) 132 64 Gregarines, conjugation and spore formation. (After Calkins and Siedlecki, modified) 133 65 Stylorhynchus oblongatus, cyst and gametes. (After Léger) 133 66 Gregarines, various spores. (After Léger) 134 67 Eimeria (Coccidium) schubergi, life-cycle diagram of. (After Schaudinn) 139 68 Eimeria avium in gut epithelium of grouse chick. (After Fantham) 143 69 Eimeria avium, life-cycle, diagram of. (After Fantham) 144 70 Eimeria stiedæ in section of rabbit’s intestine 145 71 Eimeria stiedæ, oöcysts from rabbit’s liver. (After Leuckart) 146 72 Eimeria stiedæ, spores. (After Balbiani) 146 73 Eimeria stiedæ, schizogony. (After R. Pfeiffer) 146 74 Eimeria stiedæ, section through infected nodule of liver 147 75 Isospora bigemina. (After Stiles) 150 76 Hæmoproteus (Halteridium) columbæ, life-cycle. (After Aragão, from Castellani and Chalmers) 152 77 Leucocytozoön lovati. (After Fantham) 153 78 Hæmogregarines from lizards. (After França) 154 79 Leucocytogregarina canis, life-cycle. (After Christophers, from Castellani and Chalmers) 155 80 Plasmodium vivax, life-cycle. (After Schaudinn and Grassi) 160 81 Malignant tertian malarial parasite in intestine of Anopheles. (After Grassi) 162 82 Oökinete of malignant tertian malaria in stomach of Anopheles. (After Grassi) 162 83 Section of stomach of Anopheles with malarial oöcysts. (After Grassi) 163 84 Sporulation of malarial parasites in Anopheles. (After Grassi) 163 85 Tertian malarial parasite in human red blood corpuscles. (After Mannaberg) 165 86 Quartan malarial parasite in human red corpuscles. (After Manson) 166 87 Malignant malarial parasite in human red corpuscles. (After Manson) 168 88 Malarial crescents. (After Mannaberg) 168 89 Section through tubule of salivary gland of Anopheles infected with malarial sporozoites. (After Grassi) 169 90 Nuttallia equi, life-cycle in red blood corpuscles. (After Nuttall and Strickland) 173 91 Babesia (Piroplasma) canis, life-cycle in blood of dog. (After Nuttall and Graham-Smith) 175 92 Theileria parva. (After Nuttall and Fantham) 179 93 Myxosporidian spores and infected gill of fish. (After J. Müller) 181 94 Myxobolus mülleri, spore. (After Bütschli) 181 95 Myxobolus, schema of spore. (After Doflein) 182 96 Chloromyxum leydigi. (After Thélohan) 182 97 Myxobolus pfeifferi, spore formation. (After Keysselitz, from Minchin) 183 98 Nosema apis. (After Fantham and Porter) 185 99 Nosema bombycis from silkworm. (After Balbiani) 186 100 Nosema bombycis, spores. (After Thélohan) 186 101 Hexactinomyxon psammoryctis, spore. (After Stolč) 187 102} 103} Sarcocystis miescheriana in muscle of pig. (After Kühn) 188 104 Sarcocystis miescheriana, mature trophozoite 189 105 Sarcocystis tenella in section, as seen in œsophagus of sheep 190 106 Sarcocystis tenella, young trophozoite. (After Bertram) 190 107 Sarcocystis miescheriana, end portion of trophozoite. (After Bertram) 190 108 Sarcocystis blanchardi from ox. (From Wasielewski, after van Eecke) 190 109 Sarcocystis tenella. (After Laveran and Mesnil) 191 110 Haplosporidium heterocirri. (After Caullery and Mesnil) 195 111 Haplosporidian spores. (After Caullery and Mesnil) 195 112 Rhinosporidium kinealyi, portion of ripe cyst. (After Minchin and Fantham) 197 113 Balantidium coli. (After Leuckart) 200 114 Balantidium coli, free and encysted. (After Casagrandi and Barbagallo) 200 115 Balantidium minutum. (After Schaudinn) 204 116 Nyctotherus faba. (After Schaudinn) 205 117 Nyctotherus giganteus. (After Krause) 206 118 Nyctotherus africanus. (After Castellani) 206 119 Trachoma bodies in conjunctival cells. (Original, Fantham) 209 120 Half of a transverse section through Fasciola hepatica, L. 214 121 Harmostomum leptostomum, Olss. 215 122 Median section through the anterior part of Fasciola hepatica 217 123 Polystomum integerrimum. (After Zeller) 218 124 Allocreadium isoporum, Looss. (After Looss) 218 125 Terminal flame cell of the excretory system. (Stephens) 219 126 Diagram of female genitalia. (Stephens) 220 127 Diagram of male and part of female genitalia. (Stephens) 220 128 Ovum of Fasciola hepatica, L. 223 129 Miracidium of Fasciola hepatica. (After Leuckart) 223 130 A group of cercariæ of Echinostoma sp. 225 131 Development of Fasciola hepatica, L. (After Leuckart) 226 132 Young redia of Fasciola hepatica. (From Leuckart) 227 133 Older redia of Distoma echinatum 227 134 Cercaria of Fasciola hepatica. (After Leuckart) 228 135 Encysted cercaria of Fasciola hepatica. (After Leuckart) 228 136 Watsonius watsoni. (After Shipley) 234 137 Watsonius watsoni: ventral projection composed from a series of transverse sections. (After Stiles and Goldberger) 235 138 Gastrodiscus hominis. (After Leuckart) 236 139 Fasciola hepatica, L. 238 140 Fasciola hepatica, showing the gut and its branches 239 141 Fasciola hepatica, L. (After Claus) 239 142 Fasciola hepatica: egg from liver of sheep. (After Thomas) 240 143 Limnæus truncatulus, Müll. (From Leuckart) 240 144 Young Fasciola hepatica. (From Leuckart) 242 145 Fasciola gigantica. (After Looss) 243 146 Fasciolopsis buski, Lank. (After Odhner) 245 147 Fasciolopsis rathouisi, Poir. (After Claus) 246 148 Fasciolopsis fülleborni. (After Fülleborn) 248 149 Paragonimus ringeri, Cobb. (After Katsurada) 250 150 Paragonimus ringeri, Cobb. (After Kubo) 250 150A Paragonimus westermanii, Kerb. (After Leuckart) 250 151 Egg of Paragonimus ringeri, Cobb. (After Katsurada) 251 152 Egg of Opisthorchis felineus 253 153 Opisthorchis felineus. (After Stiles and Hassall) 253 154 Opisthorchis pseudofelineus. (After Stiles) 254 155 Parapisthorchis caninus. (After Stephens) 256 156 Amphimerus noverca, Braun. (After McConnell) 257 157 Metorchis conjunctus. (After Cobbold) 258 158 Clonorchis sinensis. (After Looss) 259 159 Ova of Clonorchis sinensis. (After Looss) 259 160 Clonorchis endemicus. (After Looss) 260 161 Clonorchis endemicus: eggs. (After Looss) 260 162 Metorchis truncatus 262 163 Heterophyes heterophyes. (After Looss) 263 164 Metagonimus yokogawai. (After Leiper) 264 165 Dicrocœlium dendriticum 265 166 Eggs of Dicrocœlium dendriticum 266 167 Miracidia of Dicrocœlium dendriticum. (After Leuckart) 266 168 Echinostoma ilocanum. (After Brumpt) 268 169 Echinostoma ilocanum. (After Leiper) 268 170 Echinostoma malayanum, Leiper. (After Leiper) 269 171 Schistosoma hæmatobium. (After Looss) 270 172 Transverse section through a pair of Schistosoma hæmatobium in copulâ. (After Leuckart) 271 173 Anterior end of the male Schistosoma hæmatobium. (After Looss) 271 174 Schistosoma hæmatobium. (After Leuckart) 276 175 Schistosoma hæmatobium, ovum of. (After Looss) 277 176 Schistosoma japonicum. (After Katsurada) 278 177 Schistosoma japonicum. (After Katsurada) 279 178 Schistosoma japonicum. (After Looss) 279 179} 180} Schistosoma japonicum from dog. (After Katsurada) 280 181} 182 Schistosoma japonicum. (After Catto) 281 183 Schistosoma japonicum. (After Katsurada) 282 184 Schematic representation of a small part of a transverse section of Ligula sp. (After Blochmann) 287 185 Half of a transverse section through a proglottis of Tænia crassicollis 288 186 Dipylidium caninum. (After Benham) 289 187 Longitudinal section of the head and neck of Tænia crassicollis 290 188 Tænia cœnurus. (After Niemisec) 291 189 Young Acanthobothrium coronatum. (After Pintner) 292 190 Scolex of a cysticercoid from Arion sp. (After Pintner) 292 191 Proglottis of Tænia saginata, Goeze, showing genitalia 293 192 Dibothriocephalus latus. (After Benham and Sommer and Landois) 294 193 Diagram of genitalia of a Cestode. (Stephens) 295 194 Part of a transverse section through a proglottis of Dibothriocephalus latus 296 195 Egg of Diplogonoporus grandis. (After Kurimoto) 298 196 Uterine egg of Tænia saginata. (After Leuckart) 298 197 Oncosphere of Tænia africana (after v. Linstow) and oncosphere of Dipylidium caninum. (After Grassi and Rovelli) 299 198 Diagram of a cysticercoid. (Stephens) 301 199 Diagram of a cysticercus. (Stephens) 301 200 Diagram of development of a cysticercus. (Stephens) 303 201 Section through a piece of a Cœnurus cerebralis 304 202 Median section through a cysticercus. (After Leuckart) 304 203 Cysticercus pisiformis in an evaginated condition 304 204 Various chains of segments of Dibothriocephalus latus 311 205 Transverse section of the head of Dibothriocephalus latus 311 206 Fairly mature proglottis of Dibothriocephalus latus 311 207 Dibothriocephalus latus. (After Benham and Schauinsland) 312 208 Plerocercoid of Dibothriocephalus latus 313 209 A piece of the body wall of the Burbot, Lota vulgaris 313 210 Cephalic end of Dibothriocephalus cordatus. (After Leuckart) 315 211 Diplogonoporus grandis, Lühe, 1899. (After Ijima and Kurimoto) 317 212 Diplogonoporus grandis. (After Ijima and Kurimoto) 317 213 Cephalic end of Sparganum mansoni, Cobb. (After Leuckart) 318 214 Sparganum mansoni. (After Ijima and Murata) 318 215 Sparganum prolifer. (After Ijima) 319 216 Sparganum proliferum. (After Stiles) 319 217 Dipylidium caninum. (After Diamare) 320 218 Dipylidium caninum. (After Benham and Moniez) 320 219 Dipylidium caninum: central portion of a proglottis. (After Neumann and Railliet) 321 220 Dipylidium caninum: development of embryo. (After Benham, Grassi, and Rovelli) 321 221 Larva (cysticercoid) of Dipylidium caninum. (After Grassi and Rovelli) 322 222 Hymenolepis nana, v. Sieb. (After Leuckart) 324 223 Hymenolepis nana: head. (After Mertens) 324 224 Hymenolepis nana: an egg. (After Grassi) 324 225 Longitudinal section through the intestinal villus of a rat. (After Grassi and Rovelli) 324 226 Hymenolepis nana (murina): cross-section of proglottis from a rat. (After v. Linstow) 325 227 Hymenolepis nana: longitudinal section of an embryo. (After Grassi and Rovelli) 325 228 Hymenolepis diminuta. (After Zschokke) 326 229 Hymenolepis diminuta. (After Grassi) 326 230 Hymenolepis diminuta. (After Bizzozero) 326 231 Hymenolepis diminuta. (Stephens, after Nicoll and Minchin) 327 232 Hymenolepis lanceolata. (After Krabbe) 328 233 Hymenolepis lanceolata. (After Wolffhügel) 328 234 Scolex of Davainea madagascariensis. (After Blanchard) 330 235 Two fairly mature proglottids of Tænia solium 332 236 Head of Tænia solium 332 237 Large and small hooks of Tænia solium. (After Leuckart) 333 238 Tænia solium. (After Leuckart) 333 239 Two mature proglottids of Tænia solium 333 240 Large and small hooklets of Tænia marginata. (After Leuckart) 338 241 Mature segment of Tænia saginata 339 242 Cephalic end of Tænia saginata 339 243 Tænia saginata. (After Leuckart) 339 244 A piece of the muscle of the ox, with three specimens of Cysticercus bovis. (After Ostertag) 340 245 Mature segment of Tænia africana. (After v. Linstow) 342 246 Proglottis of Tænia africana. (After v. Linstow) 343 247 Head of Tænia africana. (After v. Linstow) 343 248 Tania confusa. (After Guyer) 344 249 Tania confusa. (After Ward) 344 250 Tania echinococcus 345 251 Echinococcus veterinorum. (After Leuckart) 347 252 } 252A} Diagrams of mode of formation of brood capsule and scolices (Stephens) 348 253 Section through an invaginated echinococcus scolex. (After Dévé) 350 254 A piece of the wall of an Echinococcus veterinorum stretched out and seen from the internal surface 350 255 Echinococcus hominis in the liver. (After Ostertag, from Thomas) 351 256 Section through an echinococcus scolex in process of vesicular metamorphosis. (After Dévé) 351 257 } 257A} Diagram of transformation of a scolex into a daughter cyst. (Stephens) 352 258 Hooklets of echinococcus. (After Leuckart) 355 259 Echinococcus multilocularis in the liver of the ox. (After Ostertag) 357 260 Diagram of a transverse section of Ascaris lumbricoides. (After Brandes) 362 261 Anterior end of an Ascaris megalocephala. (After Nassonow) 362 262 Transverse section through Ascaris lumbricoides at the level of the œsophagus behind the nerve ring. (After Goldschmidt) 364 263 Schematic representation of the nervous system of a male Ascaris megalocephala. (After Brandes) 365 264 Diagram of female genitalia 368 264A Diagram of male genitalia of a strongylid 368 265 Transverse section through the ovarian tube of Belascaris cati of the cat 369 266 Male of the rhabditic form of Angiostomum nigrovenosum 370 267 Transverse section through the posterior extremity of the body of Ascaris lumbricoides (male) 370 268 Hind end of a male Ascaris lumbricoides cut across at the level of the dilator cells of the gut. (After Goldschmidt) 371 269 A piece of the trunk muscle of the pig with encapsuled embryonic Trichinæ 373 270 Strongyloides stercoralis, female. (After Looss) 380 271 Strongyloides stercoralis, male. (After Looss) 380 272 Strongyloides stercoralis, female. (After Looss) 382 273 Strongyloides stercoralis. (After Looss) 382 274 Strongyloides stercoralis. (After Looss) 383 275 Gnathostoma siamense. (After Levinsen) 385 276 Guinea worm (Dracunculus medinensis). (After Leuckart) 387 277 Anterior extremity of Guinea worm. (After Leuckart) 387 278 Dracunculus medinensis. (After Claus) 387 279 Transverse section of female Guinea worm. (After Leuckart) 388 280 Cyclops virescens, female 389 281 Filaria bancrofti. (After Leiper) 391 282 Mf. bancrofti in thick film, dried and stained with hæmatoxylin. (After Fülleborn) 397 283 Schematic drawings of the anatomy of Ml. loa and Mf. bancrofti. (After Fülleborn) 399 284 F. demarquayi. (After Leiper) 403 285 Mf. demarquayi in thick film, dried and stained with hæmatoxylin. (After Fülleborn) 404 286 Filaria (?) conjunctivæ. (After Addario) 405 287 Filaria (?) conjunctivæ. (After Grassi) 405 288 Setaria equina. (After Railliet) 408 289 Setaria equina: anterior end. (After Railliet) 408 290 Loa loa: the anterior end of the male. (After R. Blanchard) 410 291 Loa loa: anterior portion of the female. (After Looss) 410 292 Loa loa in situ. (After Fülleborn and Rodenwaldt) 410 293 Loa loa: male and female. (After Looss) 410 294 Loa loa: the hind end of a male and of a female. (After Looss) 411 295 Loa loa: lateral view of tail of male showing papillæ. (After Lane and Leiper) 411 296 Loa loa. (After Leiper) 411 297 Mf. loa: in thick film, dried and stained with hæmatoxylin. (After Fülleborn) 413 298 Acanthocheilonema perstans. (After Leiper) 414 299 Mf. perstans. (After Fülleborn) 415 300 Dirofilaria magalhãesi. (After v. Linstow) 417 301 Trichuris trichiura 420 302 Trichinella spiralis. (After Claus) 422 303 Isolated muscular fibre of a rat, invaded by Trichinella. (After Hertwig-Graham) 425 304 Calcified Trichinella in the muscular system of a pig. (After Ostertag) 426 305 Various phases of the calcification of Trichinella of the muscles 426 306 Dioctophyme gigas. (After Railliet) 432 307 Eggs of Dioctophyme gigas. (After Railliet) 432 308 Metastrongylus apri. (Stephens) 433 309} 310} Trichostrongylus instabilis. (After Looss) 434 311} 312} Trichostrongylus probolurus. (After Looss) 435 313} 314} Trichostrongylus vitrinus. (After Looss) 436 315} 316} Hæmonchus contortus. (After Ransom) 437 316} 317 Mecistocirrus fordi. (After Stephens) 439 318 Ternidens deminutus. (After Railliet and Henry) 440 319} 320} Œsophagostomum stephanostomum var. thomasi. (After Thomas) 442 321} 322} Œsophagostomum stephanostomum var. thomasi. (After Thomas) 444 323} 324} Ancylostoma duodenale, male and female. (After Looss) 446 325 Ancylostoma duodenale, showing ventral teeth. (After Looss) 447 326 Ancylostoma duodenale: diagrammatic representation of excretory system. (After a drawing by Looss) 448 327 Ancylostoma duodenale. (After Railliet) 449 328 Ancylostoma duodenale: bursa of male. (After Looss) 450 329 Ancylostoma duodenale: eggs in different stages of development. (After Looss) 451 330 Ancylostoma duodenale: larva. (After Leichtenstern) 452 331 Ancylostoma duodenale. (After Looss) 453 332 Ancylostoma ceylanicum. (After Looss) 456 333 Ancylostoma braziliense. (After Gomez de Faria) 456 334 Necator americanus. (After Looss) 457 335 Necator americanus: lateral view. (After Looss) 458 336 Necator americanus: bursa of male. (After Looss) 458 337 Syngamus kingi: anterior end of male. (After Leiper) 460 338 Syngamus kingi: anterior end of female. (After Leiper) 460 339 Bursa of Syngamus trachealis. (Stephens) 461 340 Physaloptera mordens, Leiper, 1907. (After Leiper) 462 341 Ascaris lumbricoides. (From Claus) 463 342 Ovum of Ascaris lumbricoides 463 343 Ovum of Toxascaris limbata 466 344 Transverse section through the head part of Belascaris cati from the cat. (After Leuckart) 466 345} 346} Male female of Oxyuris vermicularis 468 347 Oxyuris vermicularis: egg freshly deposited 468 348 Oxyuris vermicularis: egg twelve hours after deposition 468 348A The male of Echinorhynchus augustatus 476 348B Anterior portion of the female apparatus of Echinorhynchus acus. (After Wagener) 476 348C Egg of Echinorhynchus gigas. (After Leuckart) 477 348D The internal organs of the leech. (After Kennel) 480 348E Hirudo medicinalis. (After Claus) 481 349 Leptus autumnalis. (After Gudden) 485 350 Leptus autumnalis. (After Trouessart) 485 351 The kedani mite. (After Tanaka) 487 352 Tetranychus telarius var. russeolus, Koch. (After Artault) 488 353 Pediculoides ventricosus. (After Laboulbène and Mégnin) 489 354 Nephrophages sanguinarius: male, ventral surface. (After Miyake and Scriba) 490 355 Nephrophages sanguinarius: female, dorsal aspect. (After Miyake and Scriba) 490 356 Tydeus molestus. (After Moniez) 491 357 Dermanyssus gallinæ. (After Berlese) 492 358 Dermanyssus hirundinis. (After Delafond) 492 359 Ixodes ricinus, male. (After Pagenstecher) 498 360 Female of Ixodes ricinus. (After Pagenstecher) 498 361 Argas reflexus. (After Pagenstecher) 506 362 Argas persicus. (After Mégnin) 507 363 Tyroglyphus farinæ: male. (After Berlese) 512 364 Tyroglyphus longior, Gerv. (After Fum. and Robin) 512 365 Rhizoglyphus parasiticus: male and female. (After Dalgetty) 514 366 Histiogaster (entomophagus ?) spermaticus. (After E. Trouessart) 515 367 Sarcoptes scabiei. (After Fürstenberg) 518 368 Sarcoptes scabiei: male, ventral aspect. (After Fürstenberg) 519 369 Sarcoptes minor var. cati. (After Railliet) 521 370 Demodex folliculorum of the dog. (After Mégnin) 522 371 Linguatula rhinaria: female 524 372 Larva of Linguatula rhinaria (Pentastoma denticulatum). (After Leuckart) 524 373 Linguatula rhinaria. (After M. Koch) 525 374 Mouth-parts of Pediculus vestimenti. (After Denny) 533 375 Ovum of the head louse 533 376 Head louse, male 533 377 Pediculus vestimenti, Burm.: adult female 533 378 Phthirius inguinalis, Leach 534 379 Head of the bed bug from the ventral surface 535 380 Dermatophilus penetrans: young female. (After Moniez) 544 381 Dermatophilus penetrans: older female. (After Moniez) 544 382 Pulex irritans 546 383 Larva of flea. (After Railliet) 546 384 Pulex serraticeps 546 385 Head of a male and of a female Anopheles. (After Giles) 549 386 Head of a male and of a female Culex. (After Giles) 549 387 Mouth-parts of Anopheles claviger. (After Grassi) 550 388 Anopheles maculipennis. (After Nuttall and Shipley) 550 389 Longitudinal section of an Anopheles, showing alimentary canal. (After Grassi) 551 390 Anopheles maculipennis, Meigen. (After Grassi) 552 391 Larva of Anopheles maculipennis, Fabr. (After Grassi) 553 392 Larva of Culex. (After Grassi) 553 393 Pupa of Anopheles maculipennis, Meig. (After Grassi) 554 394 Heads of Culex and Anopheles. (After Daniels) 556 395 Eggs of Culex, of Anopheles, of Stegomyia, of Tæniorhynchus, and of Psorophora 557 396 Diagram showing the structure of a typical mosquito. (Theobald) 558 397 Types of scales, head and scutellar ornamentation, forms of clypeus. (Theobald, etc., etc.) 559 398 Neuration of wing. Explanation of wing veins and cells. (Theobald) 560 399 Wing of Anopheles maculipennis, Meigen 566 400 Wing of a Culex 575 401 Wing of Simulium 579 402 Wing of Chironomus 579 403 A Ceratopogon, or midge 580 404 An owl midge, Phlebotomus sp. (From Giles’s “Gnats or Mosquitoes”) 581 405 Larva of Homalomyia canicularis 585 406 Larvæ of Calliphora vomitoria 585 407 Larva of Chrysomyia macellaria. (After Conil) 585 408 The screw-worm fly (Chrysomyia macellaria) 587 409 Ochromyia larva on the skin of man, South Africa. (After Blanchard) 590 410 Head end of “larva of Natal.” (After Gedoelst) 591 411 Lund’s larva. (After Gedoelst) 593 412 Dermatobia noxialis, Goudot 597 413 Larva of Dermatobia cyaniventris. (After Blanchard) 597 414 Larva of Dermatobia cyaniventris. (After Blanchard) 597 415 The ox gad fly (Tabanus bovinus, Linn.) 601 416 The brimp (Hæmatopota pluvialis, Linn.) 602 417 Head of Glossina longipalpis. (After Grünberg) 604 418 Antenna of Glossina pallidipes, male. (After Austen) 604 419 Glossina palpalis and puparium. (After Brumpt) 607 420 The tsetse-fly (Glossina morsitans, Westwood) 608 421 The stinging fly (Stomoxys calcitrans, Linn.) 609 422 Trichomonas from cæcum and gut of rat. (Original, Fantham) 735 423 Chilomastix (Tetramitus) mesnili. (Original, Fantham) 736

-------------------------------------------------------------------- |We regret to have taken without permission from the “Transactions of| |The Society of Tropical Medicine and Hygiene,” London, the following| |diagrams:-- | | | | Pages Figures | | 268 No. 169 | | 269 " 170 | | 391 " 281 | | 411 " 295 and 296 | | 414 " 298 | | 460 " 337 and 338 | | | |and tender our regret to the Society in question for having done so.| --------------------------------------------------------------------

ERRATA.

P. 31, line 6 from bottom: delete “human,” as Leidy really worked with Endamœba blattæ, parasitic in the gut of the cockroach. P. 43, line 12 from bottom: for “John’s” read “Johns.” P. 44, line 13 from bottom: for “Amœba buccalis, Sternberg,” read “Amœba buccalis, Steinberg.” P. 46, line 13 from top: for “breath” read “breadth.” P. 53, In footnote ^1, line 6 from bottom: insert “see” before _Arch. f. Protistenk_. P. 75: To paragraph regarding development of the parasite in the fly’s salivary glands, add that the crithidial phase takes two to five days. P. 111, line 8 from top: the date of Sangiorgi should be 1911. P. 142, line 7 from top: insert “Genus.” before *Eimeria*. P. 252, Insert heading “Family. *Opisthorchiidæ*, Braun, 1901,” above “Sub-family. *Opisthorchiinæ*, Looss, 1899.” P. 351, description of fig. 255, line 3: for “Thoma” read “Thomas.” P. 471, line 15 from bottom: for “alcohol 100 parts” read “alcohol 100 c.c.” P. 472, line 11 from bottom: for “Or (2) 10 per cent. formalin,” read “Or (2) fix in hot 10 per cent. formalin.” P. 493, line 21 from top: for “Conoy” read “Couvy.” P. 589, line 2 from top: for “*carnosa*” read “*carnaria*.” P. 620, line 15 from top: for “fo” read “of.” P. 622, line 12 from bottom: delete comma after quantity. P. 626, line 6 from bottom: delete comma after Mackie (1915). P. 638: insert title “*TREMATODES*” above that of “Fascioliasis.” P. 709, line 9 from bottom: omit second Pediculus capitis. P. 748, line 8 from top: for “cytologica” read “cytological.” P. 753, line 4 from bottom: for “*Fercocercous*” read “*Furcocercous*.” P. 755 line 7: for “*Oncocerca*” read “*Onchocerca*.”

ON PARASITES IN GENERAL.

By the term PARASITES is understood living organisms which, for the purpose of procuring food, take up their abode, temporarily or permanently, on or within other living organisms. There are both plants and animals (Phytoparasites and Zoöparasites) which lead a parasitic life in or upon other plants and other animals.

Phytoparasites are not included in the following descriptions of the forms of parasitism, but a very large number of animal parasites (zoöparasites) are described. The number of the latter, as a rule, is very much underrated. How great a number of animal parasites exists may be gathered from the fact that all classes of animals are subject to them. Some of the larger groups, such as Sporozoa, Cestoda, Trematoda and Acanthocephala, consist entirely of parasitic species, and parasitism even occurs among the vertebrates (Myxine). It therefore follows that the characteristics of parasites lie, not in their structure, but in the manner of their existence.

Parasitism itself occurs in various ways and degrees. According to R. Leuckart, we should distinguish between OCCASIONAL (temporary) and PERMANENT (stationary) PARASITISM. Occasional parasites, such as the flea (Pulex irritans), the bed-bug (Cimex lectularius), the leech (Hirudo medicinalis), and others, only seek their “host” to obtain nourishment and find shelter while thus occupied. Without being bound to the host, they usually abandon the latter soon after the attainment of their object (Cimex, Hirudo), or they may remain on the body of their host throughout their entire development from the hatching of the egg (Pediculus). It follows from this mode of living that the occasional parasites become sometimes distinguishable from their free-living relatives, though only to a slight extent. It is, therefore, seldom difficult to determine the systematic position of temporary parasites from their structure.

In consequence of their mode of life, all these temporary parasites live on the external surface of the body of their host, though more rarely they take up their abode in cavities easily accessible from the exterior, such as the mouth, nose and gills. They are therefore frequently called EPIZOA or ECTOPARASITES; but these designations do not cover only the temporary parasites, because numerous epizoa (as for instance the louse) are parasitic during their entire life.

In contradistinction to these temporary parasites, the permanent parasites obtain shelter as well as food from their host for a long period, sometimes during the entire course of their life. They do not seek their host only when requiring nourishment, but always remain with it, thus acquiring substantial protection. The permanent parasites, as a rule, live within the internal organs, preferably in those which are easily accessible from the exterior, such as the intestine, with its appendages. Nevertheless, permanent parasites are also found in separate organs and systems, such as the muscular and vascular systems, hollow bones and brain, while some live on the outer skin. Here again, the terms ENTOZOA and ENDOPARASITES do not include all stationary parasites; to the latter, for instance, the lice belong, which pass all their life on the surface of the body of their host, where they find shelter and food and go through their entire development. The ectoparasitic trematodes, numerous insects, crustacea, and other animals live in the same manner.

All “HELMINTHES,” however, belong to the group of permanent parasites. This term is now applied to designate certain lowly worms which lead a parasitic life (intestinal worms); but they are not all so termed. For instance, the few parasitic TURBELLARIA are never classed with the helminthes, although closely related to them. The turbellarians, in fact, belong to a group of animals of which only a few members are parasitic, whereas the helminthes comprise those groups of worms of which all species (Cestoda, Trematoda, Acanthocephala), or at least the majority of species (Nematoda), are parasitic. Formerly the Linguatulidæ (Pentastoma) were classed with the helminthes because their existence is also endoparasitic, and because the shape of their body exhibits a great similarity to that of the true helminthes. Since the study of the development of the Linguatulidæ (P. J. van Beneden, 1848, and R. Leuckart, 1858) has demonstrated that they are really degenerate arachnoids, they have been separated from the helminthes.

It is hardly necessary to emphasize the fact that the helminthes or intestinal worms do not represent a systematic group of animals, but only a biological one, and that the helminthes can only be discussed in the same sense as land and water animals are mentioned, i.e., without conveying the idea of a classification in such a grouping. It is true that formerly this was universally done, but very soon the error of such a classification was recognized. Still, until the middle of last century, the helminthes were regarded as a systematic group, although C. E. v. Baer (1827) and F. S. Leuckart (1827) strenuously opposed this view. Under the active leadership of J. A. E. Goeze, J. G. H. Zeder, J. G. Bremser, K. A. Rudolphi and F. Dujardin, the knowledge of the helminthes (helminthology) developed into a special study, but unfortunately it lost all connection with zoology. It required the intervention of Carl Vogt to disestablish the helminthes as one class of animals, by uniting the various groups with those of the free-living animals most closely related to them (Platyhelminthes, Nemathelminthes).

PERMANENT PARASITISM in the course of time has caused animals adopting this mode of life to undergo considerable, sometimes even striking, bodily changes, permanent ectoparasites having as yet undergone least alteration. The latter sometimes bear so unmistakably the likeness to the group to which they belong, that even a superficial knowledge of their structure and appearance often suffices for the recognition of their systematic position. For instance, though the louse, like many decidedly temporary parasites, has lost its wings--a characteristic of insects--in consequence of parasitism, yet nobody would deny its insect nature; such also occurs in other temporary parasites (Cimex, Pulex). On the other hand, the changes in a number of permanent ectoparasites (such as parasitic Crustacea) are far more considerable, and correspond with those that have occurred in permanent endoparasites.

These alterations depend partly on retrogression and partly on the acquisition of new peculiarities. In the former case, the change consists in the loss of those organs which have become useless in a permanent parasitic condition of existence, such as wings in the louse, and the articulated extremities seen in the larval stage of parasitic Crustacea. The loss of these organs goes hand in hand with the cohesion of segments of the body that were originally separate, and alterations in the muscular and nervous systems. In the same manner another means of locomotion is lost--the ciliated coat--which is possessed by many permanent parasites during their larval period. To all appearances, this character is not secondary and recently acquired, but represents a primary character inherited from free-living progenitors, and still transmitted to the altered descendants, because of its use during the larval stage (e.g., the larvæ of a great many Trematodes, the oncospheres of some Cestodes). Amongst the retrogressions, the loss of the organs of sense may be mentioned, particularly the eyes, which are still present, not only in the nearest free-living forms but also in the free-living larvæ of true parasites. It is only quite exceptionally that the eyes are subsequently retained, as a rule they are lost. Lastly, in a great many cases the digestive system also disappears, as in parasitic Crustacea, in a few nematodes and trematodes, in all cestodes and Acanthocephala. There remain at most the rudiments of the muscles of the fore-gut, but these are adapted to entirely different uses.

The new characters which permanent parasites may acquire are, first of all, the remarkably manifold CLASPING and CLINGING ORGANS, which are seldom (as in parasitic Crustacea) directly joined on to already existing structures. In those instances in which organs for the conveyance of food are retained, these likewise frequently undergo transformation, in consequence of the altered food and manner of feeding. Such alterations consist, for instance, in the transformation of a masticating mouth apparatus into the piercing and sucking organs of parasitic insects.

HERMAPHRODITISM (as in Trematodes, Cestodes, and a few Nematodes) is a further peculiarity of many permanent parasites; moreover, the association in couples that occurs, especially in trematodes, may lead to complete cohesion and, exceptionally, also to re-separation of the sexes. In many cases the females only are parasitic, while the males live a free life, or there may be in addition the so-called complementary males. Occasionally the male alone is parasitic, and in that case lives within the female of the same species, which may live free, like certain Gephyrea (Bonellia); or the female also may be parasitic, as Trichosoma crassicaudum, which lives in the bladder of the sewer rat (Mus decumanus).

We have numerous proofs that demonstrate how considerably the original features of many parasites have become changed. We need only draw attention to the aforementioned Linguatulidæ, also to many of the parasitic Crustacea belonging to various orders. In all of these a knowledge of the larval stages--in which there is no alteration, or at most only a slight degree of change--serves to determine their systematic position, i.e., the nearest conditions of relationship.

The most remarkable changes are observed in those groups that contain only a few parasitic members, the majority leading a free life. A striking instance is afforded by a snail, the well-known Entoconcha mirabilis, Müller. This mollusc consists merely of an elongated sac living in a Holothurian (Synapta digitata). It possesses none of the characteristics of either the Gastropoda or any molluscs, and in its interior there is nothing to be observed but the organs of generation and the embryos. Nevertheless, the Entoconcha is decidedly a parasitic snail, as is clearly proved by its larvæ, but it is a snail which, in consequence of parasitism, has lost all the characteristics of molluscs in its mature condition, but still exhibits them in the early stages of development.

Certain nematodes show very clearly to what devious courses parasitism may lead. The Atractonema gibbosum, the life-history of which has been described by R. Leuckart, and which lives in the larvæ and pupæ of a dipterous insect (Cecidomyia), exhibits, in its early stage, the ordinary characteristics of other threadworms. A few weeks later--the males having died off immediately after copulation--the females are transformed into spindle-shaped bodies, the mouth and anus of which are closed. They carry with them an irregularly shaped appendage, in which the segmenting ova are situated, and in which the further conditions of life of the Atractonema are accomplished. A minute examination has demonstrated that this appendage is the prolapsed and enlarged vagina of the animal which has become merely a supplementary attachment. The conditions present in the Sphærularia, the nematoid nature of which was long undiscovered, are still more remarkable. It was only when Siebold proved that typical nematodes were hatched from their eggs that their nature was recognized. The nematodes thus produced have not the slightest resemblance to the parent.

The researches of Lubbock, A. Schneider, and more particularly of R. Leuckart, have shown that what we call Sphærularia bombi is not an animal but merely an organ--the vagina--of a nematode worm. This vagina at first grows, sac-like, from the body of the tiny nematode; it gradually assumes enormous dimensions (2 cm. in length); it contains the sexual organs and parts of the intestine. The remaining portion of the actual animal then becomes small and shrivelled; it may be easily overlooked, being but an appendage to the vagina with its independent existence, and it finally disappears altogether.

The GREAT FERTILITY of parasites is another of their peculiarities, though this may be also the case to a certain degree with some of the free-living animals, the progeny of which are likewise exposed to enormous destruction.

More remarkable, however, is the fact that the young of the endoparasites only very exceptionally grow to maturity by the side of their parents. Sooner or later they leave the organ inhabited by the parents, frequently reach the open, and after a shorter or longer period of free existence seek new hosts. During their free period, moreover, a considerable growth may be attained, or metamorphosis may take place, or even multiplication. In the exceptional cases in which the young remain within the same host, they nevertheless usually quit the organ inhabited by the parents. They likewise rarely attain maturity within the host inhabited by the parents, but only, as in other cases, after having gained access to fresh hosts.

These transmigrations play a very important rôle in the natural history of the internal parasites, but they frequently conceal the cycle of development, for sometimes there are INTERMEDIATE GENERATIONS, which themselves invade intermediate hosts. Even when there are no intermediate generations, THE SYSTEM OF INTERMEDIATE HOSTS is frequently maintained by the endoparasites.

According to the kind of food ingested by parasites, it has recently become usual to separate the true parasites from those animals that feed on the superfluity of the food of the host, or on products which are no longer necessary to him, and to call the latter MESSMATES or COMMENSALS. As examples, the Ricinidæ are thus designated, because, like actual lice, they dwell among the fur of mammals or the plumage of birds. They do not, however, suck blood, for which their mouth apparatus is unsuited, but subsist on useless epidermic scales. These epizoa, according to J. P. van Beneden, are, to a certain extent, useful to their hosts by removing deciduous materials which under certain circumstances might become harmful to them.[1] This investigator, who has contributed so greatly to our knowledge of parasites, assigns the Ricines to the MUTUALISTS, under which term he comprises animals of various species which live in common, and confer certain benefits on one another. The mutualists are usually intimately connected in a mutually advantageous association known as “symbiosis.”[2]

[1] According to Sambon, the Ricinidæ are by no means advantageous to their hosts. These Hemipterous parasites give rise to an intolerable itching which may cause loss of rest, emaciation, and sometimes even death. Birds suffering from phthiriasis of the Ricines are usually in bad health.

[2] For further information on these conditions, see “Die Schmarotzer des Thierreichs,” by P. J. van Beneden, Leipzig, 1876; and “Die Symbiose,” by O. Hertwig.

Incidental and Pseudo Parasites.--In many cases the parasites are confined to certain hosts, and may therefore be designated as specific to such hosts. Thus, hitherto, Tænia solium and Tænia saginata in their adult condition have only been found in man; Tænia crassicollis only in the cat; Brandesia (Distoma) turgida and Halipegus (Distoma) ovocaudatas only in Rana esculenta, and so forth. In many other cases, however, certain species of parasites are common to several, and sometimes many, species of hosts; Dipylidium caninum is found in the domestic cat as well as in the dog; Fasciola hepatica is found in a large number of herbivorous mammals (nineteen species), Diplodiscus (Amphistomum) subclavatus in numerous urodele and ecaudate amphibia, Holostomum variabile in about twenty-four species of birds, and so on. In these cases the hosts are almost invariably closely related, belonging, as a rule, to the same family or order, or at any rate to the same class. Trichinella spiralis, which is found in man, and in the pig, bear, rat, mouse, cat, fox, badger, polecat and marten, and is capable of being artificially cultivated in the dog, rabbit, sheep, horse, in other mammals, and even in birds, is one of the most striking exceptions.

Some parasites are so strictly confined to one species of host that, even when artificially introduced into animals very closely related to their normal host, they do not thrive, but sooner or later, often very quickly, die off, and very rarely establish themselves. For example, repeated attempts have been made to rear the adult Tænia solium in the dog, or to rear Cysticercus cellulosæ in the ox, or the Cysticercus of Tænia saginata in the pig, but they have always proved unsuccessful. Only exceptionally has it been possible to transfer Cœnurus cerebralis, the larval stage of a tapeworm (Tænia cœnurus) of the dog from the brain of the sheep to that of the domestic goat. On the other hand, in the case of the Trichinellæ transference to a different host is easily accomplished.

Under natural conditions, it is not uncommon for certain kinds of specific parasites to occur occasionally in unusual hosts. Their relationship to the latter is that of INCIDENTAL PARASITES. Thus Echinorhynchus gigas, a specific parasite of the pig, is only an incidental parasite of man; Fasciola hepatica and Dicrocœlium lanceatum are specific to numerous kinds of mammals, but may be found incidentally in man. On the other hand, Dibothriocephalus latus, a specific parasite of man, may occasionally take up its abode in the dog, cat and fox. As a rule, all those parasites of man that are only rarely met with, notwithstanding that human beings are constantly being observed and examined by medical men, are termed INCIDENTAL PARASITES OF MAN. In many cases we are acquainted with the normal or specific host of these parasites. Thus we know the specific host of Balantidium coli, Eimeria stiedæ, Fasciola hepatica, Dipylidium caninum, etc.; in others the host is as yet unknown. In the latter case the question partly relates to such forms as have been so deficiently described that their recognition is impossible, partly to parasites of man in various regions of the earth, the Helminthes and parasites of which are totally unknown or only slightly known, or finally to early developmental stages that are difficult to identify. Animals that usually live free, and exceptionally become parasitic, may likewise be called incidental parasites. In this category are included a few Anguillulidæ that have been observed in man; also Leptodera appendiculata, which usually lives free, but may occasionally become parasitic in black slugs (Arion empiricorum): when parasitic it attains a larger size, and produces far more eggs than when living a free life. In order to avoid errors, the term “incidental parasites” should be confined to true parasites which, besides living in their normal host, may also live in other hosts. Leuckart speaks of FACULTATIVE PARASITISM in such forms as Leptodera. L. Oerley[3] succeeded in artificially causing Leptodera (Rhabditis) pellio to assume facultative parasitism by introducing these worms into the vagina of mice, where the parasites remained alive and multiplied. Leptodera pellio dies in the intestines of mammals and man; it remains alive in frogs, but always escapes into the open with the fæces.

[3] Oerley, L., “Der Rhabditiden und ihre medizinische Bedeutung,” Berlin, 1886, p. 65.

Recently the incidental parasites of man have also been called “PSEUDO-PARASITES” or “PSEUDO-HELMINTHES.” Formerly, however, these terms were applied not only to living organisms that do not and cannot live parasitically, and that only exceptionally and incidentally get into man, but also to any foreign bodies, portions of animals and plants, or even pathological formations that left the human system through the natural channels, and the true nature of which was misunderstood. Frequently these bodies were described as living or dead parasites and labelled with scientific names, as if they were true parasites. A study of these errors, which formerly occurred very frequently, would be as interesting as it would be instructive. It is better not to use the expression pseudo-parasites for incidental parasites, but to keep to the original meaning, for it is not at all certain that pseudo-parasites are not described, even nowadays.

The Influence of Parasites on the Host.--In a great many cases, we are not in a position to state anything regarding any marked influence exercised by the parasite on the organism, and on the conditions of life, of the host. Most animals and many persons exhibit few signs of such influence, an exception being infestation with helminthes and certain other parasites which produce eosinophilia in the blood. As a general rule, the parasite, which is always smaller and weaker than its host, does not attempt to endanger the life of the latter, as simultaneously its own existence would be threatened. The parasite, of course, robs its host, but usually in a scanty and sparing manner, and the injuries it inflicts can hardly be taken into account. There are, however, numerous cases[4] in which the situation of the parasites or the nature of their food, added to their number and movements, may cause more or less injury, and even threaten the life of the host. It stands to reason that a Cysticercus cellulosæ situated in the skin is of but slight importance, whereas one that has penetrated the eye or the brain must give rise to serious disorders. A cuticular or intestinal parasite is, as a rule, less harmful than a blood parasite. A helminth, such as an Ascaris lumbricoides or a tapeworm, that feeds on the residues of foodstuffs within the intestine, will hardly affect its host by depriving it of this material. The case is different when the parasites are very numerous, especially when the heavily infested host happens to be a young individual needing all it ingests for its own requirements, and therefore unable to sustain the drain of numerous intruders in the intestine. Disturbances also set in more rapidly when the intestinal helminthes are blood-suckers, the injury to the host resulting from the kind of food taken by the parasite.

[4] Lühe, M., “Ueber d. Fix. d. Helm. a. d. Darmwand ihrer Wirthe u. die dadurch verursachten path-anat. Veränderungen d. Wirthsdarmes,” Trans. of IVth Intern. Zool. Cong., Berlin, 1901; Mingazzini, P., “Ric. sul var. modo di fiss. delle tenie alla par. int. e sul loro assorbimento,” Ric. Lab. Anat. Roma e altri Lab. biol., vol. x, 1904; Shipley, A. E., and E. G. Fearnsides, “The Effects of Metazoan Parasites on their Hosts,” Journ. Econ. Biol., 1906, i, 2.

Generally, the disorders caused by loss of chyle are insignificant when compared with those induced by the GROWTH and agglomeration of the helminthes. The latter may cause chiefly obstructions of small vessels or symptoms of pressure in affected or contiguous organs, with all those complications which may arise secondarily, or they may even lead to the complete obliteration of the organ invaded. Of course the symptoms will vary according to the nature of the organ attacked.

In consequence also of the MOVEMENTS of the parasites, disorders are set up that may tend to serious pathological changes of the affected organs. The collective migrations, undertaken chiefly by the embryos of certain parasites (as in trichinosis, acute cestode tuberculosis), are still more harmful, as are also the unusual migrations of other parasites, which, incidentally, may lead to the formation of so-called worm abscesses or to abnormal communications (fistulæ) between organs that are contiguous but possess no direct connection.

Recently, several authors have called attention to the fact that the helminthes produce substances that are TOXIC to their host; and the effects of such poisons explain the pathology of helminthiasis far more satisfactorily than the theory of reflex action.

In a number of cases these toxic materials (leucomaines) have been isolated and their effects on living organisms demonstrated by actual experiments. It also appears that the absorption of materials formed by the decomposition of dead helminthes may likewise cause toxic effects. However, our knowledge of these conditions is as yet in its initial stage.[5]

[5] Moursson et Schlagdenhauffen, “Nouv. rech. clin. et phys. sur quelq. liquides organ.,” C. R. Acad. Sci., Paris, 1882, p. 791; Debove, “De l’intox. hydat.,” Bull. et Mém. Soc. méd. des Hôpit., 1888; Linstow, v., “Ueb. d. Giftgehalt d. helm.,”Internat. Monatsschr. f. Anat. u. Phys., xiii, 1896; Peiper, “Z. Symptomatol. der thier. Paras.,” Deutsche med. Wochenschr., 1897, No. 40; Mingazzini, P., “Ric. sul veleno d. elm. int.,” Rass. intern. d. med. modern. Ann., 1901, ii, No. 6; Vaullegeard, A., “Etud. exp. et crit. sur l’action d. helm.,” Bull. Soc. Linn. de Normandie, 1901, 5, Ser. T, vii, p. 84, and others.

Nearly all the symptoms caused directly or indirectly by parasites are of such a nature that the presence of the parasites cannot be diagnosed with any certainty, or only very rarely. The most that can be done is to deduce the presence of parasites by the exclusion of other causes. Fortunately, however, there are sufficient means by which we may confirm the diagnosis in a great many cases. Such means consist not only in a minute examination of the patient by palpation, percussion and local inspection, but also in the microscopical examination of the natural secretions and excretions of the body, such as sputum, nasal mucus, urine and fæces. Though such examinations may entail loss of time, they are necessary in the interest of the patient. It appears, moreover, that quackery, which has gained considerable ground even in the treatment of the helminthic diseases of man, can thus be considerably limited.

Origin of Parasites.[6]--In former times, when the only correct views that existed related to the origin of the higher animals, the mode of multiplication of parasites as well as of other lowly animals was ascribed to SPONTANEOUS GENERATION (generatio æquivoca), and this opinion prevailed throughout the middle ages. The writers on natural science merely devoted their time to the interpretation of the views of the old authors, and perpetuated the opinions of the ancients on questions, which, even in those days, could have been correctly explained merely by observation.

[6] Die Geschichte der “Klinisch wichtigen Parasiten,” behandelt H. Vierordt im “Handb. d. Gesch. d. Med. hrsg.” v. M. Neuburger u. J. Pagel, Bd. ii, 1903.

It was only when observations were again recommenced, and the microscope was invented, that the idea of spontaneous generation became limited. Not only did the microscope reveal the organs of generation or their products (eggs) in numerous animals, but Redi succeeded in proving that the so-called Helcophagi (flesh maggots) are only the progeny of flies, and never appear in the flesh of slaughtered animals when fully developed flies are prevented from approaching and depositing their eggs on it. Swammerdam likewise knew that the “worms” living in the caterpillars of butterflies were the larvæ of other insects (ichneumon flies) which had laid their eggs in their bodies; he also discovered the ova of lice. The two authors mentioned were, however, unwilling to see that the experience they had gained regarding insects applied to the helminthes. Leeuwenhoek also vehemently opposed the theory of a spontaneous generation, maintaining that, on a basis of common-sense, eggs, or at all events germs, must exist, even though they could not be seen.

The use of the microscope also revealed a large number of very small organisms in the water and moist soil, some of which undoubtedly resembled helminthes. Considering the wide dissemination of these minute organisms, it was natural to conjecture that after their almost unavoidable introduction into the human system they should grow into helminthes (Boerhave, Hoffmann). Linnæus went even further, for he traced the descent of the liver-fluke of sheep from a free-living planaria (Dendrocœlum lacteum), the Oxyuris vermicularis from free-living nematodes, and the Tænia lata (i.e., Dibothriocephalus latus) from a tapeworm (Schistocephalus solidus) found free in the water. Linnæus’ statements met with general approval. However, we must bear in mind that at that time the number of helminthes known was very small, and many of the forms that we have long ago learned to differentiate as specific were then regarded as belonging to one species. Linnæus’ statements were partly supported by similar discoveries by other investigators, such as Unzer, and partly also by the discovery of eggs in many helminthes. It was believed that the eggs hatched in the outside world gave rise to free-living creatures, and that these, after their introduction into the intestine, were transformed into helminthes. By means of these eggs the old investigators tried to explain the HEREDITARY TRANSMISSION of the intestinal worms, which was universally believed until the commencement of the last century. Some authors went so far as to regard the intestinal worms as congenital or inherited; they maintained the possibility of direct transmission, as in suckling, and denied that the eggs reaching the external world had anything to do with the propagation of the parasites.

The more minute comparison between the supposed free-living stages of the helminthes and their adult forms, and the impossibility of finding corresponding free forms for the ever-increasing number of parasitic species, revealed the improbability of Linnæus’ statements (O. Fr. Müller). It was the latter author also who recognized the origin of the tapeworms (Schistocephalus, Ligula) found free in the water. They originate from fishes which they quit spontaneously.

However, in spite of the fact that van Doeveren and Pallas correctly recognized the significance of the eggs in the transmission of intestinal worms, these statements remained disregarded, as did Abildgaard’s observation, experimentally confirmed, that the (immature) cestodes from the abdominal cavity of sticklebacks became mature in the intestines of aquatic birds. Moreover, at the end of the eighteenth and the commencement of the nineteenth centuries, after helminthology had been raised to a special branch of study by the successful results of the investigations of numerous authors (Goeze, Bloch, Pallas, Müller, Batsch, Rudolphi, Bremser), many of whom experienced a “divine joy” in searching the intestines of animals for helminthes, some authors reverted to generatio æquivoca, without, however, entirely denying the existence of organs of generation and eggs. The fact that a few nematodes bore living progeny--a fact of which Goeze was already aware--had no influence on the erroneous opinion, as in such cases it was considered that the young continued to develop beside the old forms. There were also many helminthes known that never developed sexual organs and never produced eggs, and which therefore were referred to generatio æquivoca. People were convinced that the intestinal mucous membrane or an intestinal villus could transform itself into a worm, either in a general morbid condition of the body, or in pathological changes of a more local character. The appearance of helminthes was even regarded as useful and as a means for the expulsion of injurious matter.

These views, firmly rooted and supported by such eminent authorities as Rudolphi and Bremser, could not easily be overthrown. First, a change took place in the knowledge of the trematodes. In 1773, O. Fr. Müller discovered Cercariæ living free in water. He regarded them as independent creatures and gave them the name that is still used at the present time. Nitzsch, who also minutely studied these organisms and who recognized the resemblance of the anterior part of their bodies to a Fasciola, did not, however, arrive at a correct conclusion. He regarded the combination rather as that of a Fasciola with a Vibrio, for which he mistook the characteristic tail of the cercaria. He also noticed the encystment (transformation into the “pupa”) on foreign bodies of many species of these animals, but was of opinion that this process signified only the termination of life.

Considerable attention was attracted to the matter when Bojanus first published a paper entitled “A Short Note on Cercaria and their Place of Origin.” He pointed out that the cercariæ creep out of the “royal yellow worms,” which occur in freshwater snails (Limnæa, Paludina), and are probably generated in these worms.

Oken, in whose journal, Isis (1818, p. 729), Bojanus published his discovery, remarks in an annotation, “One might lay a wager that these Cercariæ are the embryos of Distomes.” Soon after (1827), C. E. v. Baer was able to confirm Bojanus’ hypothesis that the cercariæ as a “heterogeneous brood” originated from spores in parasitic tubes in snails (germinating tubes). Moreover, Mehlis (Isis, 1831, p. 190) not only discovered the opercula of the ova of Distoma, but likewise saw the infusorian-like embryo emerge from the eggs of Typhlocœlum (Monostomum) flavum and Cathæmasia (Distoma) hians. A few years later (1835) v. Siebold observed the embryos (miracidia) of the Cyclocœlum (Monostomum) mutabile, and discovered in their interior a cylindrical body that behaved like an independent being (“necessary parasite”), and was so similar in appearance to the “royal yellow worms” (Bojanus) that Siebold considered the origin of the latter from the embryos of trematodes as, at all events, possible. Meanwhile, v. Nordmann of Helsingfors had in 1832 seen the miracidia of flukes provided with eyes swimming in water; v. Siebold (1835) had observed the embryos, or oncospheres, of tapeworms furnished with six hooklets in the so-called eggs of the Tænia; while Creplin (1837) had discovered the “infusorial” young of the Diphyllobothrium (Bothriocephalus) ditremum, and conjectured that similar embryos were to be found in other cestodes with operculated eggs. At all events, the fact was established that the progeny of the helminthes appeared in various forms and was partly free living. The researches of Eschricht (1841) were likewise of influence, as they elucidated the structure of the Bothriocephali, and proved that the encysted and sexless helminthes were merely immature stages.

J. I. Steenstrup (1842) was, however, the first to furnish explanations for the numerous isolated and uncomprehended discoveries. Commencing with the remarkable development of the Cœlenterata, he established the fact that the Helminthes, especially the endoparasitic trematodes, multiply by means of alternating and differently formed generations. Just as the polyp originating from the egg of a medusa represents a generation of medusæ, so does the germinal tube (“royal yellow worm”) originating from the ciliated embryo of a Distoma, etc., represent the cercaria. These were consequently regarded as the progeny of trematodes, and Steenstrup, guided by his observations, conjectured that the cercaria, whose entrance into the snails he had observed accompanied by the simultaneous loss of the propelling tail, finally penetrated into other animals, in which they became flukes.

Part of this hypothetical cycle of development was erroneous, and in other particulars positive observation was lacking, but the path pursued was in the right direction. Immediately after the appearance of Steenstrup’s celebrated work, v. Siebold expressed his opinion that the encapsuled flukes certainly had to travel, i.e., to be transmitted with their bearers into other hosts, before becoming mature. This view was experimentally confirmed by de Filippi, La Valette St. George (1855), as well as by Pagenstecher (1857), while the metamorphosis of the ciliated embryo of Distoma into a germinal tube was first seen by G. Wagener (1857) in Gorgodera (Distoma) cygnoides of frogs. All that we have subsequently learned from the works of numerous investigators about the development of endoparasitic trematodes has certainly increased our knowledge in various directions, and, apart from the deviating development of the Holostomidæ has, as a whole, confirmed the briefly sketched cycle of development.

Steenstrup’s work on the cestodes did not attract the same attention as his work on trematodes. Steenstrup always insisted on the “nurse” nature of the cysticerci and other bladder-worms. Abildgaard (1790), as well as Creplin (1829 and 1839), had already furnished the information that certain sexless cestodes (Schistocephalus and Ligula) from the abdomen of fishes only become mature after their transference to the intestine of aquatic birds. These passive migrations were confirmed in an entire series of other cestodes, particularly by v. Siebold (1844, 1848, 1850) and E. J. van Beneden (1849), not by actual experiment, but by undoubted observation.

It was correctly believed that the ova or oncospheres penetrate into certain intermediate hosts, in which they develop into unsegmented larvæ. Here they remain until, with their host, they are swallowed by some predacious animal. They then reach the intestine, being freed from the surrounding membranes through the process of digestion, and settle themselves there to form the adult chain of proglottides. Though some few scientists, such as P. J. van Beneden and Em. Blanchard, deduced from these observations that the bladder-worms (Cysticerci), which had hitherto been regarded as a separate class of helminthes, were only larval Tæniæ, this correct view was not at first universally accepted. The foundation was too slight, and van Beneden was of opinion that the Cysticerci were not necessary, but only appeared incidentally.

v. Siebold was a strenuous opponent to this theory, notwithstanding his experiences on the change of hosts of the Tetrarhynchus. Together with Dujardin (1850) he conjectured that the Tæniæ underwent a deviating cycle of development. He was of opinion that the six-hooked oncospheres left the intestine, in which the older generation lived, and were scattered about with the fæces, and finally re-entered per os (i.e., with water and food) a host similar to the one they had left, in the intestine of which they were directly transformed into tapeworms. A change of host such as occurred in other cestodes was not supposed to take place (the history of the cestodes was at this time not entirely established). As the oncospheres of the Tænia are enveloped in one calcareous or several softer coverings which they cannot leave actively, and as, in consequence of this condition, innumerable oncospheres cannot penetrate into an animal, and others cannot reach the proper animal, v. Siebold conceded, at least for the latter, the possibility of a further development. But this was only supposed to occur because they had either invaded wrong hosts, or, having reached the right hosts, had penetrated organs unsuitable to their development, and had thus gone astray in their travels, and had become hydropically degenerated tæniæ. This was v. Siebold’s explanation of bladder-worms. Naturally, v. Siebold himself conjectured that a recovery of the diseased tapeworm might occur, in a few exceptional cases, after transmission into the correct host, as, for instance, in the Cysticercus fasciolaris of mice, the host of which is the domestic cat, and in which there is a seemingly normally developed piece of tapeworm situated between the caudal vesicle and the cysticercus head.

Guided by correct views, F. Küchenmeister undertook in Zittau the task of confirming the metamorphosis of Cysticercus pisiformis of hares and rabbits, into tapeworms in the intestine of the dog by means of feeding experiments. The first reports on the subject, published in 1851, were not likely to meet with universal approval, because Küchenmeister first diagnosed the actual tapeworm he had been rearing as Tænia crassiceps, afterwards as Tænia serrata, and finally as Tænia pisiformis n. sp. However, in any case, Küchenmeister, by means of the reintroduction of experimental investigation, rendered a great service to helminthology.

The publication of Küchenmeister’s works induced v. Siebold to undertake similar experiments (1852 and 1853), which were partly published by his pupil Lewald in 1852. But the positive results obtained hardly changed Siebold’s opinion, for although he no longer considered the bladder-worms as hydropically degenerated tapeworms, he still regarded them as tæniæ that had strayed. The change of opinion was partly due to an important work of the Prague zoologist, v. Stein (1853). He was able to examine the development of a small bladder-worm in the larvæ of the well-known meal-worm (Tenebrio molitor) and to demonstrate that, as Goeze had already proved in the case of Cysticercus fasciolaris of mice, first the caudal vesicle is formed and then the scolex, whereas Siebold believed that in bladder-worms the posterior end of the scolex was formed first, and that this posterior end underwent a secondary hydropic degeneration.

In opposition to v. Siebold, Küchenmeister successfully proved the necessity of the bladder-worm stage by rearing tapeworms in dogs from the Cysticercus tenuicollis of domestic mammals and from the Cœnurus cerebralis of sheep. He, and simultaneously several other investigators independently, succeeded, with material provided by Küchenmeister, in rearing the Cœnurus cerebralis in sheep from the oncospheres of the Tænia cœnurus of the dog (1854). R. Leuckart obtained similar results in mice by feeding them with the mature proglottides of the Tænia crassicollis of cats (1854).

Küchenmeister also repeatedly reared the Tænia solium of man from the Cysticercus cellulosæ of pigs (1855), and from the embryos of this parasite P. J. van Beneden succeeded in obtaining the same Cysticercus in the pig (1854). As Küchenmeister distinguished the Tænia mediocanellata, known to Goeze as Tænia saginata, amongst the large tæniæ of man (1851), so it was not long before R. Leuckart (1862) succeeded in rearing the cysticercus of the hookless tapeworm in the ox. It is particularly to this last-named investigator that helminthology is indebted more than to any other author. He followed the gradual metamorphosis from oncospheres to cystic worms in all its details.

In view of all the researches that were made, and which are too numerous to mention individually, the idea that bladder-worms are abnormal or only incidental forms had to be abandoned. Everything pointed to the fact that in all cestodes the development is divided between two kinds of animals; in one--the host, the adult tapeworm is found; while in the other, the intermediate host, we find some form or other of an intermediate stage (cysticercus in the broadest sense). The practical application of this knowledge is self-evident. If no infected pork or beef is ingested, no tapeworm can be acquired, and also the rearing of cysticerci in the human body is prevented by avoiding the introduction of the eggs of tapeworms.

Though these results were definitely proved by numerous researches, yet they have been repeatedly challenged, notably by J. Knoch (1862) in Petrograd, who, on the basis of experiments, sought to confirm a direct development without an intermediate host and ciliated stage, at all events as regards Dibothriocephalus latus. However, the repeated communications of this author met with but little favour from competent persons, partly because the experiments were conducted very carelessly, and partly because their repetition on dog and man (R. Leuckart) had no results (1863). It was only in 1883 that Braun was able to prove that the developmental cycle of Dibothriocephalus latus is similar to that of other Cestodes. The results obtained in other places by Parona, Grassi, Ijima and Zschokke render any discussion of Küchenmeister’s conclusions unnecessary.[7] Long after Knoch, a French author, P. Mégnin, also pleaded for the direct development of some cestodes, and especially some tæniæ. He (1879) also sought to prove a genetic connection between the hookless and armed tapeworms of mammals, but the arguments he adduced, so far as they rest on observations, can be easily refuted or attributed to misinterpretation. Only one of these arguments is correct, namely, that the number of the species of tæniæ with which we are acquainted is far larger than that of the corresponding cystic forms; but this disparity alone cannot be taken as a proof of direct development. It can only be said that our knowledge in this respect is deficient. As a matter of fact, we have during recent years become acquainted with a large number of cystic forms, hitherto unknown, belonging to tæniæ which have long been familiar. It must also be borne in mind that no man in his lifetime can complete an examination for bladder-worms of the large number of insects, for instance, which may destroy an entire generation of an insectivorous species of bird within a small district.

[7] Refer to the collected literature under Dibothriocephalus latus, and the reply to Küchenmeister by Braun (“Ueber den Zwischenwirt des breit. Bandw.” Würzb.: Stuber, 1886).

Naturally it does not follow that direct development in the cestodes is altogether lacking. The researches of Grassi (1889) have furnished an example in Hymenolepis (Tænia) murina, which shows that development may sometimes take place without an intermediate host, notwithstanding the retention of the cystic stage. It was found that the oncospheres of this species, introduced into rats of a certain age, after a time grow into tapeworms without leaving the intestine, but not directly, for they bore into the intestinal wall, where they pass the cystic stage, the cysts afterwards falling into the intestinal lumen, where they develop into tapeworms. The recent experiments of Nicoll (1911) show that the larval stages of Hymenolepis murina also occur in the rat-flea, Ceratophyllus fasciatus.

Important observations were soon made on the remaining groups of helminthes. The discussion on the origin of parasites soon became confined to the helminthes. Amongst the Nematoda, it had long been known that encapsuled forms existed that had at first been regarded as independent species, but very soon they were pronounced to be immature forms, in consequence of their lack of sexual organs. Though Dujardin and also v. Siebold regarded them as “strayed” animals, v. Stein (1853) very promptly demonstrated that the progeny of the nematodes were destined to travel by discovering a perforating organ in the larval nematodes of the mealworm. This was first experimentally confirmed (1860) by R. Leuckart, R. Virchow and Zenker, all of whom succeeded not only in bringing to maturity the muscle Trichinæ (known since 1830) in the intestine of the animals experimented upon, but were likewise able to follow the migrations of the progeny. Of course, the encapsulating brood remained in the same organism, and in this respect deviated from the broods of other helminthes which escape into the outer world and find their way into other animals, but the encapsuled nematodes could no longer be regarded as the result of straying. Subsequently, R. Leuckart worked out, more or less completely, the history of the development of numerous nematodes, or pointed out the way in which further investigations should be made. It has been found that in nematodes far more frequently than in other helminthes, the typical course of development is subject partly to curtailment and partly to complications, which sometimes considerably increase the difficulties of investigation and have hitherto prevented the attainment of a definite conclusion, though the way to it is now clear.

In a similar manner the works of R. Leuckart have cleared up the development of the Acanthocephala and Linguatulida. Of course, much still remains to be done. So far, we do not even know all the helminthes of man and of the domestic animals in all their phases of life, and still less is known of those of other animals. We are indebted to the discoveries of the last fifty years for the knowledge arrived at, though comparatively few names are connected with it. The gross framework is revealed, but the gaps have only been filled up here and there. However, we may trustfully leave the completion of the whole to the future, without fear that any essential alterations will take place.

The deductions to be drawn are as follows: That the helminthes like the ectoparasites multiply by sexual processes, that the entire course of development of the helminthes is rarely or never gone through in the same host as is the case with several ectoparasites, that the progeny at an earlier or later stage of development, as eggs, embryos, or larvæ, quit the host inhabited by the older generation, and almost always attain the outer world: only in Trichinella does the development take place directly in the definite host. Where the eggs have not yet developed they go through the embryonic evolution in the outer world. The young larvæ are transmitted, either still enclosed within the egg or embryonic covering, to the intermediate host or more rarely they are transferred straight to the final host. In other cases they may hatch out from their envelopes, and after a longer or shorter period of free life, during which they may partake of food and grow, they, as before, penetrate, usually in an active way, into an intermediate host, or at once invade the final host. Exceptionally (e.g., Rhabdonema), during the free life there may be a propagation of the parasitic generation, and in this case only the succeeding generation again becomes parasitic, and then at once reaches its final host. The young forms which have invaded the final host become mature in the latter, or after a longer or shorter period of parasitism again wander forth (as the Œstridæ, Ichneumonidæ, etc.), and reach the adult stage in the outer world. The young stages, during which the parasites undergo metamorphoses or are even capable of producing one or several intermediate generations, are passed in the intermediate hosts until, as a rule, they are passively carried into the final host and there complete their cycle of development by the formation of the organs of generation. This mode of development, the spending of life in two different kinds of animals (intermediate and final host), is typical of the helminthes. This is manifested in the Acanthocephala, the Cestoda, the majority of the endoparasitic Trematoda, a number of the Nematoda, and the Linguatulidæ. There are now and then exceptions, however, in which, for instance, the host and intermediate host change order (Trichinella, Hymenolepis murina).

Parasites are hardly ever inherited amongst animals.[8] According to a few statements, however, Trichinella and Cœnurus are supposed to be transmissible from the infected mother to the fœtus. Otherwise most animals acquire their parasites, especially the Entozoa, from without, the parasites penetrating either actively, as in animals living in the water, or passively with food and drink. A particular predisposition to worms is not more likely than a spontaneous origin of parasites.

[8] However, in the Protozoa there are examples of hereditary transmission of parasites, e.g., in the case of Babesia (Piroplasma) bovis and Babesia canis in their invertebrate hosts (ticks); in Crithidia melophagia and Crithidia hyalommæ; and in the case of Spirochæta duttoni in its invertebrate host (a tick).

Derivation of Parasites.--Doubt now no longer exists as to the derivation of the temporary and of many of the stationary ectoparasites from free-living forms. This conclusion is founded on the circumstance that not only are there numerous intermediate degrees in the manner of living and feeding between predacious and parasitic animals, but that there is more or less uniformity in their structure. The differences that exist are easily explained as consequences of altered conditions of life. The case is more difficult in regard to groups that are exclusively parasitic (Cestoda, Trematoda, Acanthocephala, Linguatulidæ, and Sporozoa), or groups that are chiefly parasitic (Nematoda), because in these cases the gulf that divides these forms from free-living animals is wider. It is true that we know that the nearest relatives of the Linguatulidæ are found amongst the Arachnoidea, and indeed in the Acarina; that, moreover, the structure and development of the Sporozoa refers them to the Protozoa, and allows some of them to be regarded as the descendants of the lowest Rhizopoda. We know that the Trematoda, and through these the Cestoda, are closely related to the Turbellaria, from which they may be traced. The Nematoda, and still more the Acanthocephala, stand apart. This is less evident, however, in the Nematoda, for there are numerous free-living members of these from which it is possible that the parasitic species may be descended. Indeed, this seems more than probable if such examples as Leptodera, Rhabdonema and Strongyloides are taken into consideration, as well as the conditions of life of free-living nematodes. These mostly, if not exclusively, spend their lives in places where decomposing organic substances are present in quantities; some species attain maturity only in such localities, and there propagate very rapidly. Should the favourable conditions for feeding be changed, the animals seek out other localities, or they remain in the larval form for some time until more favourable conditions set in. It is comprehensible that such forms are very likely to adopt a parasitic manner of life which at first is facultative (Leptodera, Anguillula), but may be regarded as the transition to true parasitism. The great advantages attached to a parasitic life consist not only in protection, but also in the supply of suitable food, and consequently in the easier and greater production of eggs, and thus fully account for the gradual passage of facultative parasitism into true parasitism. In many forms the young stages live free for some time (Strongylidæ), in others, as is the case in Rhabdonema, parasitic and free-living generations alternate; in others, again, the free period is limited to the egg stage or entirely suppressed.

Though it is possible thus to connect the parasitic with the free-living nematodes, by taking their manner of life into account, this matter presents greater difficulties in regard to other helminthes. It is true that the segmented Cestoda may be connected with and traced from the less known and interesting single-jointed Cestoda (Amphilina, Archigetes, Caryophyllæus, Gyrocotyle). Trematodes are all parasites, with the exception of one group, Temnocephalidæ, several genera and species of which live on the surface of the bodies of Crustacea and turtles of tropical and sub-tropical freshwaters. Temnocephalidæ are, nevertheless, predacious. They feed on Infusoria, the larvæ of small insects and Crustacea. So far as is known they do not nourish themselves on part of the host. They belong to the group of commensals, or more correctly, to that of the SPACE PARASITES, which simply dwell with their host and do not even take a portion of the superfluity of its food. However, space parasitism may still be regarded as the first stage of commensalism, which is again to be regarded as a sort of transition to true parasitism.

It is possible that parasitism came about in this way in the trematodes, in which connection we must first consider the turbellaria-like ancestors of the trematodes. Much can be said in favour of such a genetic relationship between turbellaria and trematodes, and hardly anything against it. It should also be remembered that amongst the few parasitic turbellaria there are some that possess clinging discs or suctorial pores, and these are only differentiated from ectoparasitic trematodes by the possession of a ciliated integument, which is found only in the larval stages of the latter.

The Acanthocephala occupy an isolated position. Most authors certainly regard them as related to the nematodes; in any case, the connection is not a close one, and the far-reaching alterations which must have occurred prevent a clear view. Perhaps the free original forms of Acanthocephala are no longer in existence, but that such must have existed is a foregone conclusion.

An explanation of the CHANGE OF HOST so frequent in parasites is more difficult than that of their descent. R. Leuckart is of opinion that the present intermediate hosts, which belong principally to the lower animals, were the original hosts of the parasites, and fostered both their larval and adult stages. It was only in course of time that the original hosts sank to the position of intermediate hosts, the cause for this alteration being that the development of parasites, especially of the helminthes, through further development and differentiation extended over a larger number of stages. The earlier stages remained in their original hosts, but the later stages sought out other hosts (higher animals). To prove this, Leuckart points out that the mature stages of the helminthes, with but few exceptions, occur only in the vertebrates which appeared later in the development of the animal kingdom, while the great majority of intestinal worms of the lower animals only represent young stages, which require transmission into a vertebrate animal before they can become mature. The few helminthes that attain maturity in the lower animals (Aspidogaster, Archigetes) are therefore regarded by Leuckart as primitive forms, and he compares them with the developmental stages of helminthes, Aspidogaster with rediæ, Archigetes with cysticercoids. He classes the nematodes that become mature in the invertebrates with Anguillulidæ, i.e., with saprophagous nematodes from which the parasitic species descend.

Leuckart therefore regards the change of hosts as secondary, so does Sabatier. The latter, however, adduces other reasons for this (lack of clinging organs and the necessity to develop them in an intermediary stage); but in this connection he only considers the Cestoda. In opposition to Leuckart, R. Moniez, however, is convinced that the migrations of the helminthes, as well as the system of intermediate hosts, represent the original order of things. Moniez traces all Entozoa from saprophytes, but only a few of these were able to settle directly in the intestine and there continue their development. These are forms that at the present day still lack an intermediate host, such as Trichocephalus, Ascaris, and Oxyuris. In most other cases the embryos, however, consisted of such saprophytes as were, in other respects, suitable to become parasites, but were incapable of resisting the mechanical and chemical influences of the intestinal contents. They were therefore obliged to leave the intestine at once, and accomplished this by penetrating the intestinal walls and burrowing in the tissues of their carriers. In this position, assisted by the favourable conditions of nutrition, they could attain a relatively high degree of development. Mechanical reasons prevented a return to the intestines, where the eggs could be deposited. Most of them doubtless died off as parasites, as also their young stages do at present when they penetrate wrong hosts. Some of them, nevertheless, passively reached the intestine of beasts of prey. Many were destroyed in the process of mastication; for a small part, however, there was the chance of reaching the intestine of a beast of prey undamaged, and there, having become larger and more capable of resistance, maturity was attained. By means of this incidental coincidence of various favourable circumstances, these processes, according to Moniez, have been established by heredity and have become normal.

This is not the place to express an opinion either for or against the various hypotheses advanced, but the existence of these diametrically opposed views alone will show the great difficulty of the question. Independently, however, it appears more natural to come to the conclusion that parasitism, as well as change of hosts, were gradual transitions.

As a conclusion to this introductory chapter, a list of some of the most important works on the parasitology of man and animals is appended.

LITERATURE.

GOEZE, J. A. E. Versuch einer Naturgeschichte der Eingeweidewürmer thierischer Körper. Blankenburg, 1782. 4to, 471 pp., with 44 plates.

ZEDER, J. G. H. Erster Nachtrag zur Naturgeschichte der Eingeweidewürmer. von J. A. E. Goeze. Leipzig, 1800. 4to, with 6 tables.

RUDOLPHI, C. A. Entozoorum sive vermium intestinalium historia naturalis. I, Amstelod., 1808; ii, 1809. 8vo, with 18 plates.

RUDOLPHI, C. A. Entozoorum synopsis. Berol., 1819. 8vo, with 3 plates.

BREMSER, J. G. Ueber lebende Würmer im lebenden Menschen. Wien, 1819. 8vo, with 4 plates.

BREMSER, J. G. Icones helminthum, systema Rudolphii entozoologicum illustrantes. Viennae, 1824. Fol. (Paris, 1837).

DUJARDIN, F. Histoire naturelle des helminthes ou vers intestinaux. Paris, 1845. 8vo, with 12 plates.

DIESING, C. M. Systema helminthum. 2 vols. Vindobonnae, 1850, 1851. 8vo. Supplements by the same author: Revision der Myzhelminthen (Report of the Session of the Imp. Acad. of Science. Wien, xxxii, 1858); with addendum (ibid., xxxv, 1859); Revision der Cephalocotyleen (ibid., xlix, 1864, and xlviii, 1864); Revision der Nematoden (ibid., xlii, 1861); Supplements (ibid., xliii, 1862).

BENEDEN, P. J. VAN. Mémoire sur les Vers intestinaux. Paris, 1858. 4to, with 12 plates.

KÜCHENMEISTER, F. Die in und an dem Körper des lebenden Menschen vorkommenden Parasiten. Leipzig, 1855. 8vo, with 14 plates.

LEUCKART, R. Die menschlichen Parasiten und die von ihnen herrührenden Krankheiten. I, Leipzig, 1863; II, Leipzig, 1876. 8vo.

COBBOLD, T. Sp. Entozoa; an Introduction to the Study of Helminthology. London, 1864. 8vo. Supplement, London, 1869.

DAVAINE, C. Traité des entozoaires et des maladies vermineuses de l’homme et des animaux domestiques. 2nd edit. Paris, 1877. 8vo.

LINSTOW, O. V. Compendium der Helminthologie, ein Verzeichniss der bekannten Helminthen, die frei oder in thierischen Körpern leben, geordnet nach ihren Wohnthieren, unter Angabe der Organe, in denen sie gefunden sind, und mit Beifügung der Litteraturquellen. Hanov., 1878. 8vo. Supplement, including the years 1878–1888, Hanov., 1888.

COBBOLD, T. Sp. Parasites; a Treatise on the Entozoa of Man and Animals, including some Account of the Entozoa. London, 1879. 8vo.

LEUCKART, R. Die Parasiten des Menschen und die von ihnen herrührenden Krankheiten. 2nd edit. Leipzig, 1879–1886. The Protozoa, Cestodes, Trematodes and Hirudinea have hitherto appeared (continued by Brandes).

BÜTSCHLI, O. Protozoa in Bronn’s Klass. u. Ordn. d. Thierreichs. Vol. i, Leipzig, 1880–1889. 8vo, with 79 plates.

BRAUN, M. Trematodes in Bronn’s Klass. u. Ordn. d. Thierreichs. Vol. iv, 1, Leipzig, 1879–1893. 8vo, with 33 tables. (The first thirteen sheets, comprising the history of the worms up to 1830, were compiled by H. Pagenstecher.)

ZÜRN, F. A. Die thierischen Parasiten auf und in dem Körper unserer Haussäugethiere, sowie die durch erstere veranlassten Krankheiten, deren Behandlung und Verhütung. 2nd edit. Weimar, 1882. 8vo, with 4 plates.

COBBOLD, T. Sp. Human Parasites; a Manual of Reference to all the Known Species of Entozoa and Ectozoa. London, 1882. 8vo.

KÜCHENMEISTER, F., and F. A. ZÜRN. Die Parasiten des Menschen. 2nd edit. Leipzig, 1888., 8vo, with 15 plates.

BLANCHARD, R. Traité de zoologie médicale. I, Paris, 1889; II, 1890. 8vo.

NEUMANN, L. G. Traité des maladies parasitaires non microbiennes des animaux domestiques. 2nd edit. Paris, 1892. 8vo. English edit., translated by G. Fleming. 2nd edit., revised by J. Macqueen. 1905. London: Baillière, Tindall and Cox.

LOOSS, A. Schmarotzerthum in der Thierwelt. Leipzig, 1892. 8vo.

RAILLIET, A. Traité de zoologie médicale et agricole. 2nd edit. I, Paris, 1895. 8vo.

PARONA, C. L’elmintologia italiana da’ suoi primi tempi all’ anno 1890. Genova, 1894. 8vo.

BRAUN, M. Cestoda in Bronn’s Klass. u. Ordn. d. Thierreichs. Vol. iv, 2, Leipzig, 1894–1900. 8vo, with 24 plates.

MOSLER, F., and E. PEIPER. Thier Parasit. (Spec. Path. u. Ther. v. H. Nothnagel. Vol. vi.) Wien, 1894. 8vo, with 124 illustrations.

LAVERAN, A., et R. BLANCHARD. Les hématozoaires de l’homme et des anim. Paris, 1895. 12mo, with 30 figs.

SLUITER, C. R. De dierl. paras. v. d. mensch en van onze huisdier. Haag, 1895. 8vo.

BLANCHARD, R. Malad. parasit., paras. animaux, paras. végét. à l’exclus. des bacter. (Traité de pathol. gén. de Ch. Bouchard, vol. ii.) Paris, 1895. 8vo, with 70 figs.

HUBER, J. CH. Bibliographie der klin. Helminthol. München, 1895. 8vo. With Supplement, 1898, and continued as Bibl. d. klin. Entomol. München, 1899–1900.

MONIEZ, R. Traité de parasitol. anim. et veget. appl. à la médecine. Paris, 1896. 8vo, with 116 figs.

WEICHSELBAUM. Parasitologie (Weil’s Handb. d. Hyg.). Jena, 1898. 8vo, with 78 illustrations.

KRAEMER, A. Die thierischen Schmarotzer des Auges (Gräfe and Sämische’s Handb. d. ges Augenheilk.). Leipzig, 1899. 8vo, with 16 illustrations.

CHOLODKOWSKY, N. A. Icones helm. hominis. St. Petersburg, 1898–99. Fol. (atlas with 15 plates).

PERRONCITO, E. I parassiti dell’ uomo e degli animali utili e le più comuni malattie da essi prodotti. II_{a} ed. Milano 1902. 8^o. con 276 fig. e 25 tav.

STILES, Ch. W. and A. HASSALL. Index Catalogue of Medicine and Veterinary Zoology. Washington, 1902 (U.S. Dept. of Agric., Bur. of Anim. Ind., Bull. No. 39).

NEVEU-LEMAIRE, M. Précis de parasitologie humaine, parasites végétaux et animaux. 4^e édit. Paris, 1911.

HOFER, B. Handbuch der Fischkrankheiten. München, 1904. 8^o. 18 Taf. 222 Abb.

GUIART, J., and L. GRIMBERT. Précis de Diagnostic chimique, microscopique et parasitologique. Paris, 1906. With 500 figs.

OSTERTAG, R. Handbuch der Fleischbeschau. V. Aufl. mit 265 Abb. Stuttgart, 1904.

STILES, Ch. W. The International Code of Zoological Nomenclature as applied to Medicine (Hygienic Lab., Bull. No. 24, Washington, 1905).

STILES, C. W., and HASSALL, A. Trematoda and Trematode Diseases. (Index Catalogue of Med. and Vet. Zoology.) Hygienic Lab., Bull. No. 37, Washington, 1908.

STILES, C. W., and HASSALL, A. Cestoda and Cestodaria. Hygienic Lab., Bull. No. 85, Washington, 1912.

LALOY, L. Parasitisme et mutualisme dans la nature. Paris, 1906. 8vo, 284 pp., 82 figs.

THEOBALD, F. V. A Monograph of the Culicidæ of the World. 5 vols. and plates. 1901–1910. London: Brit. Museum, Nat. Hist.

JAMES, S. P., and LISTON, W. G. The Anopheline Mosquitoes of India. 2nd edit. 1911. Calcutta: Thacker, Spink and Co.

HOWARD, L. O., DYAR, H. G., and KNAB, F. The Mosquitoes of North and Central America and the West Indies. 2 vols. 1912. Washington: Carnegie Institution.

AUSTEN, E. E. African Blood-sucking Flies. 1909. London: Brit. Museum, Nat. History.

AUSTEN, E. E. A Handbook of Tsetse-flies. 1911. London: Brit. Museum, Nat. History.

CASTELLANI, A., and CHALMERS, A. J. Manual of Tropical Medicine. 2nd edit. 1,747 pp. 1913. London: Baillière, Tindall and Cox.

KOLLE and WASSERMANN. Handbuch der pathogenen mikroorganismen. Jena: Gustav Fischer.

MINCHIN, E. A. An Introduction to the Study of the Protozoa. 1912. London: Arnold.

LAVERAN, A., et MESNIL, F. Trypanosomes et Trypanosomiases. 2nd edit. 1912. Paris: Masson and Co.

DOFLEIN, F. Lehrbuch der Protozoenkunde. 3rd edit. 1911. Jena: Gustav Fischer.

NUTTALL, G. H. F., WARBURTON, C., COOPER, W. F., and ROBINSON, L. E. Ticks--a Monograph of the Ixodoidea. Pt. I (1908). Pt. II. (1911). University Press, Cambridge, England.

BRUMPT, E. Précis de Parasitologie. 2nd edit. 1913. Paris: Masson and Co.

PATTON, W. S., and CRAGG, F. W. A Text-book of Medical Entomology. 1913. Christian Literature Society of India: London, Madras, and Calcutta.

JOURNALS.

For current researches the following, among others, should be consulted:--

Annals of Tropical Medicine and Parasitology, Liverpool. Annales de l’Institut Pasteur, Paris. Archives de Parasitologie, Paris. Archives de Zoologie Expérimentale et Générale, Paris. Archiv für Protistenkunde, Jena. Archiv für Schiffs- und Tropen-Hygiene, Leipzig. Bulletin of Entomological Research, London. Bulletin de l’Institut Pasteur, Paris. Bulletin de la Société de Pathologie Exotique, Paris. Bulletins of the Bureau of Animal Industry, Washington. Centralblatt für Bakteriologie und Parasitenkunde, Jena. Compt. Rend. Acad. Sci., Paris. Compt. Rend. Soc. Biol., Paris. Indian Journal of Medical Research, Calcutta. Journal of Experimental Medicine, New York. Journal of Medical Research, Boston. Memorias do Instituto Oswaldo Cruz, Rio de Janeiro. Parasitology, Cambridge. Proceedings of the Royal Society, London. Quarterly Journal of Microscopical Science, London. Review of Applied Entomology, London. Tropical Diseases Bulletin (London: Tropical Diseases Bureau). Zeitschrift für Infektionskrankheiten, Berlin.

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THE ANIMAL PARASITES OF MAN

Man is one of those organisms in on on which a whole host of parasites find conditions suitable for their existence: Protozoa, Platyhelminthes, Nematoda, Acanthocephala, Hirudinea, and a large number of Arthropoda (Arachnida as well as Insects) all include members which are parasites of man. These animals either live on the external surface of the body or within the intestine and its appendages. Other organs and systems are not quite free from foreign organisms--we are acquainted with parasites in the skeletal system, in the circulatory system, in the brain, in the muscles, in the excretory and genital organs, and even in the organs of sense.

It is possible, and perhaps might be advantageous, to arrange and describe the parasites of man according to the situations in which they are found (parasites of the skin, intestinal parasites, etc.). Their description in the various stages of development would, however, be disturbed when, as is generally the case, the different stages are passed in different organs, and a work which treats more fully of the natural history of the parasites than of the local disorders to which they give rise would suffer thereby. It is, therefore, preferable to describe the parasites of man in their systematic order, and to mention their different situations in man in describing each species.

A. *PROTOZOA*,

BY

H. B. FANTHAM, M.A., D.Sc.

All those animal organisms which throughout their entire life never rise above the unicellular stage, or merely form simple, loose colonies of similar unicellular animals, are grouped under the term Protozoa (Goldfuss, 1820), as the simplest types of animal life. All the vital functions of these, the lowest forms of animals, are carried out by their body substance, the protoplasm (sarcode). Often particular parts possess special functions, but the limits of a cell are never over-stepped thereby. These special parts of the cell are called “cell-organs”; recently they have been termed “organellæ.”

The living protoplasm has the appearance of a finely granular, viscid substance which, as a rule, when not surrounded by dense investing membranes or skeletons, exhibits a distinct kind of movement, which has been termed amœboid. According to the species, processes of different forms and varying numbers called pseudopodia are protruded and withdrawn, and with their assistance these tiny organisms glide along--it might almost be said flow along--over the surface. In most Protozoa two layers of cytoplasm may be recognised, and distinguished by their appearance and structure, namely, the superficially situated, viscid, and quite hyaline ectosarc or ectoplasm, and the more fluid and always granular endosarc or endoplasm, which is entirely enveloped by the ectoplasm. The two layers have different functions; the movements originate from the ectoplasm, which also undoubtedly fulfils the functions of breathing, introduction of food and excretion. The endoplasm, which in some forms (Radiolaria) is separated from the ectoplasm by a membrane, undertakes the digestion of the food. To this distribution of functions between the various layers of cytoplasm is due the development of particular cellular organs, such as the appearance of cilia, flagella, suctorial tubules (in the Suctoria) and the myophan striations, which are contractile parts of the ectoplasm in Infusoria and Gregarines. In many cases (Flagellata, Ciliata), an area is differentiated for the ingestion of food (oral part, cytostome) to which there is often added a straight or curved opening (cytopharynx), through which the food reaches the endoplasm. The indigestible residue is either cast off through the oral part or excreted by a special anal part (cytopyge). In rare cases, structures sensitive to light, the so-called pigment or eye spots are developed, e.g., Euglena. In the case of Infusoria the endoplasm circulates slowly, and agglomerations of fluids (food vacuoles) sometimes appear around each bolus of food; in these vacuoles the food is digested under the action of certain materials (ferments). Even in the lowliest Protozoa fluids to be excreted are, as a rule, gathered into one, or, more rarely, several contractile vacuoles, which regularly discharge their contents. This action, however, is to a certain extent governed by the temperature of the surrounding medium. In some Infusoria a tube-like channel in the cytoplasm is joined to the contractile vacuole which usually occupies a certain position; this forms a sort of excretory duct, and there are also supply-canals leading to these organellæ.

Very frequently various substances are deposited in the endoplasm, such as fatty granules, drops of oil, pigment granules, bubbles of gas or crystals. More solid skeletal substances are secreted in or on the ectoplasm. To the latter belong the cuticle of the Sporozoa and Infusoria, the chalky shells containing one or several chambers of the Foraminifera, the siliceous and very ornamental framework of the Radiolaria, and the chitinous coat of many Flagellata, Infusoria, etc. Some forms make use of foreign bodies found in their surroundings, such as grains of sand, to construct their protective coverings.

The food often consists of small animal or vegetable organisms and of organic waste; it is usually introduced in toto into the endoplasm. On the other hand, the Suctoria extract nourishment from their prey by means of their tentacles. Many parasitic species also ingest solid food, others feed by endosmosis.

In all cases one nucleus at least is present. It is true that the existence of non-nucleated Protozoa, the so-called Monera, is still insisted upon, but some of these have already proved to be nucleated, and the presence of nuclei in the others will no doubt be established. Very often the number of nuclei increases considerably, but these multinucleate stages are always preceded by uninucleate stages. In the Infusoria, in addition to the larger or principal nucleus (macronucleus) there is usually a smaller reproductive nucleus (micronucleus). This dualism of the nuclear apparatus is considered by some to be general, and usually to appear first at the onset of reproduction.

The form and structure of the nucleus vary greatly in different species. There are elongate, kidney-shaped, or even branched nuclei as well as spherical or oval ones. In addition to vesicular nuclei with a distinct karyosome and incidentally also with a nuclear membrane, homogeneous and more solid formations are frequently encountered. The nuclei are always differentiated from the protoplasm by their reactions, particularly in regard to certain stains.

In many Protozoa an extra-nuclear mass, sometimes compact, sometimes diffuse, arises from or near the nucleus. This mass, whose staining reactions resemble those of the nucleus, is termed the chromidial apparatus. On the dualistic hypothesis, two varieties of chromidia occur, one originating from the vegetative nucleus (macronucleus), being chromidia in the restricted sense, the other derived from the reproductive or micronucleus being termed sporetia. Chromidia consist of altered (? katabolic) nuclear material.

The nucleus plays the same part in the life of the single celled organisms as it does in the cells of the Metazoa and Metaphyta. It appears to influence in a certain manner all, or at least most, of the processes of life, such as motility, regeneration, growth, and generally also digestion. Its principal influence, however, is exercised in the propagation of the cells, as this is always brought about by the nucleus.

The PROPAGATION of the Protozoa is effected either by division or by means of direct budding. In division, which is preceded by direct or indirect (mitotic) division of the nucleus, the body separates into two, several, or even a great many segments. In this process the entire substance of the body is involved, or a small residual fragment may be left, which does not undergo further division and finally perishes. In the budding method of multiplication a large number of buds are formed, either on the surface or in the interior of the organism. Where divisions or buddings follow one another rapidly, without the segments separating immediately after their production, numerous forms develop, which are often unlike the parental forms, and these are termed swarm spores or spores. Divisions imperfectly accomplished lead to the formation of protozoal colonies.

Sometimes encystment[9] takes place previous to division. Frequently, also, sexual processes appear, such as the union of two similar (isogamous) or dissimilar (anisogamous) individuals. In the latter case sexual dimorphism occurs, with the formation of males (microgametes) and of females (macrogametes). The union may be permanent (copulation), the process being comparable with the fertilisation of the ovum by a spermatozoon. On the other hand, attachment may be transient (conjugation) when, after the exchange of portions of the nucleus, the couple separate, to multiply independently of each other. Sometimes there is an ALTERNATION OF GENERATIONS, as there may be several methods of propagation combined in the same species, either direct multiplication, conjugation, or copulation being practised; the different generations may thus, in certain cases, be unlike morphologically.

[9] Independently of propagation, many protozoa protect themselves from death by encystment when the water in which they are living dries up; in this condition the wind may carry them over wide tracts of land.

Protozoa inhabit salt water as well as fresh water; they are also found on land in very damp places, and invade animals as parasites.

CLASSIFICATION OF THE PROTOZOA.

Class I.--*Sarcodina* (Rhizopoda). Protozoa, the body substance of which forms pseudopodia; many of them are capable of developing chitinous, chalky, or siliceous coverings or skeletal structures, which, however, permit the protrusion of the pseudopodia either over the entire periphery or at certain points. They possess one nucleus or several.

Order 1.--Amœbina (Lobosa) naked or with a simple shell, sometimes formed of a foreign substance; the pseudopodia may be lobose or finger-shaped; there may be a contractile vacuole; generally only one nucleus. They live in fresh or salt water, in the soil, and also parasitically.

Order 2.--Foraminifera (Reticularia). Mostly provided with a calcareous shell, usually consisting of several chambers, and allowing the protrusion of the pseudopodia either at the periphery or only at the opening. The pseudopodia are filamentous and frequently anastomosed; there is no contractile vacuole; there are usually several nuclei. Mostly marine.

Order 3.--Heliozoa. Naked, or with a chitinous or simple radial siliceous skeleton; the pseudopodia are filamentous, and are frequently supported by firmer axes, which exhibit no tendency to anastomosis; there is a contractile vacuole; one or several nuclei. Live in fresh water.

Order 4.--Radiolaria. The body has radially-disposed filamentous pseudopodia, and the nucleus is hidden in the central capsule; there is almost always a siliceous framework, consisting of pieces arranged radially, tangentially, or lattice-like; there is no contractile vacuole, but fluid-containing hydrostatic vacuoles are present in the peripheral protoplasm. Marine.

Class II.--*Mastigophora* (Flagellata). Protozoa with one or several long flagella used for locomotion and for acquiring food; in stationary forms their only function is to take in food. Cytostome and contractile vacuole may be present. May be either naked or provided with protective coverings; one or more nuclei. They live either in fresh or salt water, or may be parasitic.

This class is again divided into several sub-classes and orders, of which only the Euflagellata, with the Protomonadina and Polymastigoda are of interest here.

Class III.--*Sporozoa.* Protozoa that only live parasitically in the cells, tissues, or organs of other animals. They ingest liquid food by osmosis; the surface of the body is covered with an ectoplasmic layer, or cuticle; they have no cilia in the adult state, but may form pseudopodia. Flagella occur, but only on the male propagating individuals. There may be one or numerous nuclei, but no contractile vacuole. Propagation by means of spores, mostly provided with sporocysts, is characteristic.

Sub-class 1.--*Telosporidia.* These are usually of constant form, rarely amœboid; they are uninucleate in the mature state; they live within host cells in the first stage. Spore-formation occurs at the end of the life-cycle.

Order 1.--Gregarinida. Body of a constant, usually elongate form, surrounded by a cuticle. In the early stage they lead an intracellular existence; in the mature stage they live within the intestine or body cavity of invertebrate animals, especially the Arthropoda, and, like intestinal parasites, are provided with clinging organs. Copulation usually isogamous; the spores have coats (chlamydospores) and usually contain several minute germs (sporozoites).

Order 2.--Coccidiidea. Body of uniform spherical or oval shape: they lead an intracellular life, but are not freely motile in cavities of the body. Fertilization is anisogamous; the spores have coats or shells (sporocysts), and usually contain several sporozoites. Exhibit alternation of generations.

Order 3.--Hæmosporidia. Parasites of the blood corpuscles of vertebrate animals; they exhibit amœboid movement; fertilization is anisogamous; many present alternation of generations and hosts; spores naked.

Sub-class 2.--*Neosporidia.* They are multinucleate when adult, and the form of the body varies exceedingly (often amœboid); spore-formation commences before the completion of growth.

Order 1.--Myxosporidia. The spores have valvular coats, with or without caudal appendages, with two, rarely four, polar capsules. They live free in such organs as the gall or urinary bladder, but are chiefly found in connective tissue. They occur especially in fishes.

Order 2.--Microsporidia. Spores with coats or sporocysts; no caudal appendage, with one polar capsule. They usually live in the tissues of Arthropoda.

Order 3.--Sarcosporidia. Elongate parasites of the muscular fibres of amniotic vertebrates, on rare occasions they occur also in the connective tissue; the spores, which are kidney or sickle-shaped, are naked and apparently have no obvious polar capsule.

Order 4.--Haplosporidia. Simple organisms, forming simple spores; they occur in Rotifers, Polychætes, Fish and Man.

Class IV.--*Infusoria* (Ciliata). The body is generally uniform in shape, with cilia and contractile vacuole, frequently also with cytostome; usually has macro- and micro-nucleus; live free in water and also parasitically.

The orders Holotricha, Heterotricha, Oligotricha, Hypotricha and Peritricha are classified according to the arrangement of the cilia.

Class V.--*Suctoria.* Bodies with suctorial tubes, contractile vacuoles, macro- and micro-nucleus, no cytostome. They generally invade aquatic animals as cavity parasites, yet also attack plants; early stage ciliated. Live sometimes as parasites on Infusoria. [The Suctoria are frequently regarded as a sub-class of the Infusoria.]

The Protozoa and Protophyta are sometimes united under the term Protista (Haeckel, 1866). The Spirochætes are Protists (see pp. 114–128).

Class I. *SARCODINA*, Bütschli, 1882.

Order. *Amœbina*, Ehrenberg.

A. *Human Intestinal Amœbæ.*

The first record of the occurrence of amœba-like organisms in the human intestine, that is, in intestinal evacuations, was that of Lambl (1859); nevertheless, the case was not quite conclusive, as the occurrence of testaceous amœbæ of fresh water (Arcella, Difflugia) was also reported. In 1870 Lewis found amœbæ associated with disorders of the large intestine in patients in Calcutta. A year later Cunningham reported from the same locality that he had observed on eighteen occasions, in one hundred examinations of dejecta from cholera patients, colourless bodies with amœboid movements, which became encysted and multiplied by fission. The daughter forms were said to be capable of dividing again, but they might also remain in contact. Contractile vacuoles were not noticed. The same bodies were observed also in simple diarrhœa (twenty-eight cases out of one hundred.)

The case reported by Lösch in 1875 attracted more attention. It was that of a peasant, aged 24, who came from the province of Archangel. He was admitted into Eichwald’s clinic at Petrograd with symptoms of dysentery. In the discharges containing blood and pus, Lösch found amœbæ in large numbers. When at rest these amœbæ measured from 20 µ to 35 µ; in a state of movement their length might extend up to 60 µ (fig. 1). The pseudopodia appeared only singly, and, since they were hyaline (ectoplasmic), were thus distinguished from the markedly granular endoplasm that enclosed a spherical nucleus of from 5 µ to 7 µ in diameter. One or more non-contractile vacuoles were present. Quinine enemata had the effect of making the amœbæ disappear from the fæces and thus causing the diarrhœa to abate. Four months after admission the patient died from the results of intercurrent pneumonia. At the autopsy ulceration of the large intestine was found, especially in the lower parts. Lösch connected the amœbæ with the ulcerations by experiments made on four dogs by injecting them with recently passed stools (per os et anum). Eight days after the last injection numerous amœbæ were found in the fæces of one of these dogs; eighteen days after the injection the animal was killed. The mucosa of the rectum was inflamed, covered with blood-stained mucus and ulcerated in three places. Numbers of amœbæ were found both in the pus of the ulcers and in the mucus. The three other dogs remained healthy. From these observations Lösch concluded that the species of amœba described by him as Amœba coli could not be regarded as the primary cause of the disease, but that it was certainly capable of increasing a lesion of the large intestine already present, or at least of preventing its healing.

B. Grassi (1879) found in the stools of healthy as well as in those of diarrhœic patients from various localities in Northern Italy, amœbæ similar to those discovered by Lösch. As this was of frequent occurrence, the pathogenicity could not be definitely established. Normand, formerly naval surgeon at Hong-Kong, observed numerous amœbæ in the dejecta of two patients suffering from colitis.

Many further investigations, which cannot be quoted in detail, showed not only that intestinal amœbæ were widely distributed in man, but indicated with greater certainty their rôle as agents of dysentery. The Commission sent out by the German Government in the year 1883 to investigate cholera in India and Egypt--whose members discovered the cholera bacillus--also collected information with regard to dysentery. In five cases of dysentery examined post mortem at Alexandria, with the exception of one case in which ulceration of the colon had already cicatrized or was approaching cicatrization, R. Koch found amœbæ as well as bacteria in sections from the base of the ulcers, although such had previously escaped notice in examination of the dejecta. Encouraged by these results, Kartulis (1885), who had discovered amœba-like bodies in the stools of patients suffering from intestinal complaints at Alexandria, continued his investigations. The results, obtained from more than 500 cases, gave rise to the theory that typical dysentery was caused by amœbæ as were also the liver-abscesses that often accompany it. Kartulis supported his theory not only by the regular occurrence of amœbæ in the stools of dysenteric patients and their absence in other diseases, and by the occurrence of the parasites in ulcers of the large intestine and in the pus from liver-abscesses, but also by experiments which he performed on cats. These were infected by injection per anum of stool material rich in amœbæ from subjects of dysentery. The infection took place also when amœba-containing, but bacteria-free, pus from liver-abscesses was used. It has been objected that the infection of man with Amœba coli, as the dysenteric amœbæ were then generally designated, does not take place per anum but per os. This difficulty, however, diminished in proportion as the encysted states of amœbæ (fig. 2), long known in the case of other Protozoa, became understood. The infection of man (Calandruccio, 1890) and of cats (Quincke and Roos) succeeded solely when material containing such stages was used. Amœbæ introduced into the intestine multiply there by fission (Harris, 1894). However, this theory, to which various other authors gave support on the grounds of their own observations, encountered opposition. Thus it was established that amœbæ were not found in patients in every place where dysentery was endemic, or else they were much rarer than was expected. Further, amœbæ were present in the most varied kinds of intestinal diseases, both of infective and non-infective characters. Also they were present in quite healthy persons.

Moreover, for various reasons, infection experiments on animals failed to supply proof, and finally a bacterium was discovered (Shiga, 1898) to be the excitant of one form of dysentery. Agglutination attested the specific part played by this organism, as it was produced by the blood serum of a person suffering from or recovered from dysentery, but not by the serum of one who was uninfected. Bacillary dysentery consequently was a distinct entity. The final step to be taken was to decide whether there was a specific amœbic enteritis (amœbic dysentery or amœbiasis, according to Musgrave).

This question should decidedly be regarded from the positive point of view. It is intimately connected with another, namely, whether there are not several species of intestinal amœbæ. The possibility of this had already been recognized. In addition to the Amœba coli Lösch, R. Blanchard distinguished yet another, Amœba intestinalis, and designated thereby the large amœbæ described in the first communication made by Kartulis; later on he stated the distinction between the species. Councilman and Lafleur[10] (1891) considered the amœba of dysentery to be Amœba coli Lösch and so re-named the species Amœba dysenteriæ. Kruse and Pasquale (1893) employed the same nomenclature, but retained the old name Amœba coli Lösch for the non-infectious species. Quincke and Roos (1893) set forth three species: a smaller species (25 µ) finely granular, pathogenic for men and cats (Amœba coli Lösch); a larger species (40 µ) coarsely granular, pathogenic for men but not for cats (A. coli mitis); and a similar species non-pathogenic either for man or cat (A. intestini vulgaris). Celli and Fiocca (1894–6) went still further, they distinguished:

(1) Amœba lobosa variety guttula (= A. guttula Duj), variety oblonga (= A. oblonga Schm.) and variety coli (= A. coli Lösch).

(2) Amœba spinosa n. sp. occurring in the vagina as well as in the intestine of human patients suffering from diarrhœa and dysentery.

(3) Amœba diaphana n. sp. found in the human intestine in cases of dysentery.

(4) Amœba vermicularis Weisse, present in the vagina and in dysentery; and

(5) Amœba reticularis n. sp. in dysentery.

[10] “Amœbic Dysentery,” Johns Hopkins Hosp. Repts., ii, pp. 395–548, 7 plates.

Shiga distinguished two species; a larger pathogenic species with a somewhat active movement, and a small harmless species with a somewhat sluggish movement. Bowman mentions two varieties, Strong and Musgrave (1900) two species--the pathogenic Amœba dysenteriæ and the non-pathogenic Amœba coli; Jäger (1902) and Jürgens (1902) mention at least two species. In the following year (1903) a work by Schaudinn was published which marked a real advance. This, in conjunction with the establishing of a special genus (Endamœba or Entamœba) for human intestinal amœbæ first by Leidy[11] and then by Casagrandi and Barbagallo,[12] for the time cleared up the confused nomenclature, the old name Amœba coli being retained for the harmless intestinal amœbæ of man, whereas the pathogenic species was designated Entamœba histolytica. The history of more recent work is incorporated in the accounts of the entamœbæ given below.

[11] “On Amœba blattae,” Proc. Acad. Nat. Sci., Philadelphia (1879), xxxi, p. 204.

[12] “Entamœba hominis s. Amœba coli (Lösch).” Annali d’Igiene speriment. (1897), vii, p. 103. See also further remarks on p. 34.

*Entamœba coli*, Lösch, 1875, emend. Schaudinn, 1903.

Syn.: Amœba coli, Lösch, 1875. Entamœba hominis, Casagr. et Barbag. 1897.

The amœboid trophozoite, according to Lösch, measures 26 µ to 30 µ and upwards; according to Grassi 8 µ to 22 µ; according to Schuberg 12 µ to 26 µ. A separation of the body substance into ectoplasm and endoplasm is only perceived during movement. The pseudopodia, which are generally only protruded singly, are broad and rounded at the end (lobopodia) and are hyaline, while the remainder of the body is granular. The ectoplasm is less refractile than the rest of the cytoplasm; it also stains less intensely (fig. 1), and is best seen on protrusion of a pseudopodium. Red blood corpuscles are rarely, if ever, found ingested in the cytoplasm.

The nucleus is vesicular, and is spherical when inactive, measuring 5 µ to 7 µ, with a thick nuclear membrane. In the centre of the nucleus is a chromatinic body or karyosome or sometimes several small nuclear bodies formed of plastin and chromatin; the remaining chromatin is arranged on the achromatic network in the form of fine granules, especially thickly deposited on the nuclear membrane.

Entamœba coli lives as a commensal in the upper portion of the large intestine, where the fæces still possess a pulpy consistency. With their concentration and change in reaction lower in the bowel, the parasites either die or else if they are at a suitable stage of development form resistant cysts. These cysts (fig. 2) can be found in great abundance in normal fæces, as Grassi first observed. Slight laxantia or intestinal diseases of any kind producing increased peristalsis, however, show amœbæ even in the unencysted condition, provided that the person harbours intestinal amœbæ generally. The intensity of infection varies according to the locality; thus Schaudinn found that 50 per cent. of the persons examined were infected with harmless amœbæ in East Prussia, 20 per cent. in Berlin and about 66 per cent. on the Austrian littoral.

The life-history (fig. 3) of the parasite exhibits two phases: (a) asexual multiplication in the intestine, either by binary fission or by schizogony with formation of eight merozoites, and (b) sporogony leading to the production of eight-nucleate cysts. Infection results from ingestion of cysts. Only cysts with eight nuclei are infective. The diameter of such cysts is about 15 µ to 20 µ.

There are varying accounts of the details of the life-cycle of Entamœba coli in its different stages. Thus, regarding schizogony or multiple fission it was formerly stated that the nucleus of the parent amœba divided into eight portions, which after dissolution of the nuclear membrane, passed outwards into the cytoplasm, which segregated around each. Eight merozoites were thus produced. More recently the process of schizogony has been considered to consist in the repeated division of the nucleus into two, four, and finally eight nuclei (fig. 3, A-D), and the formation of eight merozoites or amœbulæ.

The process of encystment is initiated by the extrusion of all liquid and foreign bodies from the protoplasm, which assumes a spherical form (fig. 4, A). The rounded uninucleate amœba then secretes a soft gelatinous coat, which finally differentiates into a double contoured cyst wall in older cysts. According to Casagrandi and Barbagallo, the size of the cyst varies from 8 µ to 30 µ, and averages about 15 µ. According to Schaudinn (1903) the cytological changes during cyst formation are as follows. The nucleus of a rounded uninucleate form divides into two (fig. 4, B). Each of these nuclei fragments into chromidia (fig. 4, C), some of which are absorbed, while others reunite so that the cell becomes binucleate again. Each of these nuclei, by a twice repeated division, produces three nuclei (fig. 4, D), the smaller two of which degenerate and were regarded as reduction nuclei. There is a clear zone or vacuole in the middle of the cyst during these maturation processes, dividing the cyst into two halves. After the nuclear reduction the clear space disappears, and each nucleus (termed by some a gamete nucleus) divides into two pronuclei (fig. 4, E). The pronuclei of the pairs were said by Schaudinn to differ slightly. Copulation occurs between pairs of unlike pronuclei, and is an example of autogamy (fig. 4, F). When complete, each of the fusion nuclei (synkarya) divides twice, giving rise first to four and finally to eight nuclei. Eight amœbulæ are thus formed within the cyst.

According to Hartmann and Whitmore (1911)[13], however, autogamy does not occur within the cysts of E. coli. They consider that eight small amœbulæ are formed (fig. 3, 2-10) which escape from the cyst and then conjugate in pairs (fig. 3, 10-12), afterwards growing into a new generation of trophozoites.

[13] Archiv f. Protistenkunde, xxiv, p. 182.

Only some 10 to 20 per cent. of the cysts evacuated with the fæces undergo the full course of development, the majority perish previously. In old dry fæces, only cysts with eight nuclei are found, and it is these alone that cause the infection.

Entamœba williamsi, E. bütschlii, E. hartmanni and E. poleki (Prowazek) are probably only varieties of E. coli.

The principal feature distinguishing Entamœba coli from E. histolytica is the formation of eight-nucleate cysts by the former as contrasted with the tetra-nucleate cysts of the latter. The cyst-wall of E. coli is thicker than that of E. histolytica (tetragena). Further, E. coli does not usually ingest red blood corpuscles, nor are “chromidial blocks” present inside its cyst (see p. 40).

According to Chatton and Lalung-Bonnaire[14] (1912) the entamœbæ of vertebrates should be placed in a separate genus Löschia, as they differ in their life-history from E. blattæ, the type species of Entamœba. Leidy (1879), however, named the genus Endamœba, but further researches are necessary on biological variation among these organisms.

[14] Bull. Soc. Path. Exotique, v, p. 135.

*Entamœba histolytica*, Schaudinn, 1903.

Syn.: Amœba coli, autt. p. p. Amœba dysenteriæ, autt. p. p.

The average size of the amœboid trophozoite is 25 µ to 30 µ. In fæces diluted with salt solution the amœbæ swell to 40 µ and more. There is sometimes separation of the body substance into a strongly refractile vitreous ectoplasm and a corneous endoplasm, pronounced even in repose, although the former is not equally thick at all parts of the periphery. In the endoplasm generally there are numerous foreign bodies (bacteria, epithelial cells, colourless and red blood corpuscles (fig. 6), and occasionally living flagellates of the intestine). The nucleus is 4 µ to 6 µ in diameter, and may be difficult to recognize because it is sometimes weakly refractile and poor in chromatin. Its shape is slightly variable; it is usually excentric, sometimes wholly peripheral at the limit of the two parts of the body. Vacuoles are not present in quite fresh specimens, but appear later. In the study of E. histolytica, the morphological characters of the trophozoite or vegetative stage of the organism formerly separated as E. tetragena (figs. 5, 6, 8_a_) must be considered (see p. 38).

The history of the development of these species, which give rise to amœbic enteritis as distinguished from bacillary dysentery, was formerly not so well known as that of E. coli. Upon being introduced into cats (per anum) dysenteric amœbæ provoke symptoms similar to those in man. In the latter, besides metastatic liver abscesses, abscesses of the lungs, and, according to Kartulis, cerebral abscesses are occasionally produced. Marchoux (1899) states that when the disease has lasted for some time liver abscesses are produced in cats also.

In the large intestine of infected cats the amœbæ creep over the epithelium, and here and there they force the epithelial cells apart, as well as removing them or pushing them in front of them; the amœbæ thus insert themselves into the narrowest fissures. They penetrate also into the glands through the epithelium, and thence into the connective tissue of the mucosa. Intestinal and glandular epithelia perish under the influence of these parasites: the cells are pushed aside, fall to pieces or are absorbed by the amœbæ. In the connective tissue of the mucosa the amœbæ migrate further, and often accumulate above the muscles. Finally they rupture this and force their way into the submucosa. In cats, apparently, the penetration is not so great as in men, according to Kruse and Pasquale. During their migration the parasites also gain access to the lymph-follicles of the wall of the intestine, which become swollen and commence to suppurate; follicular abscesses arise and after their rupture follicular ulcers. The diseased patches in the mucosa are markedly hyperæmic and numerous hæmorrhages are set up. Roos and Harris state that the amœbæ also penetrate into the blood-vessels (fig. 7) and this explains the occurrence of metastatic abscesses.[15] The whole submucosa is severely swollen at the diseased spot and undergoes small-celled infiltration in the neighbourhood of the colonies of amœbæ. From these findings Jürgens (1902) draws the conclusion[16] which is followed here, that the amœbæ are causative agents of the enteritis of cats, which disease is well defined, both pathologically and anatomically. Subsequent researches confirm the experience of earlier authors; great precautions were taken to exclude errors, hence, as with Gross and Harris, no exception can be taken to their results. The inoculation material was derived from soldiers who suffered from amœbic enteritis in China and who were admitted into the garrison hospital at Berlin. In order to be independent of the patients themselves, transmission experiments from cat to cat were performed, after the first experiments on cats yielded positive results. This was also effected by rectal feeding as employed by earlier workers. Such appeared necessary in order to prevent the evacuation of the inoculation material per anum, as well as to avoid the employment of morphia and ether narcosis. Forty-six cats were used for the experiments. Ten cats received tested stools containing motile amœbæ from soldiers suffering from amœbic enteritis contracted in China. Sixteen other cats received stools from cats infected by inoculation. All the animals sickened and suffered from the disease. Five cats received dejecta from human amœbic enteritis in which, however, no motile amœbæ were present. Thirteen cats received stools from soldiers who suffered from bacillary dysentery. None of the latter cats took the complaint and none showed changes in the large intestine upon sectioning. The injection of various bacteria, obtained from a stool of amœbic enteritis pathogenic to cats, remained without result in both the cats employed for this experiment. Lastly, two cats, which had been kept with those artificially infected, were taken ill spontaneously and suffered from the disease. In the opinion of Harris, who ascertained the harmless nature of bacteria derived from the intestinal flora containing dysenteric amœbæ, young dogs are capable of being infected.

[15] Lung abscesses generally arise by the bursting of a liver abscess through the diaphragm into the right lower lobe of the lung, sometimes also through conveyance of amœbæ by means of the blood-stream (Banting).

[16] These findings were confirmed by Schaudinn by means of investigations on cats and men. Cf. also Alfred Gross, Marchoux, P. G. Woolley, W. E. Musgrave, H. F. Harris and others.

Within the large intestine an active increase of Entamœba histolytica must occur. Nevertheless, Jürgens did not definitely find changes that might be interpreted in this sense. Schaudinn (1903) observed division and gemmation in vivo. Both processes, in which the nucleus divides by amitosis, can only be distinguished by the fact that the daughter individuals are similar in binary fission but dissimilar in gemmation, whether they make their appearance singly or in greater numbers. Schizogony, resulting in the formation of eight individuals, which is so characteristic for Entamœba coli, was not observed. (But schizogony, into four merozoites, is now known to occur. Gemmation processes are apparently degenerative.)

Resistant stages, which serve for transmission to other hosts, are according to Schaudinn[17] first formed when the diseased portions commence to heal, or more accurately, the recovery commences when the vegetative increase of the amœbæ in the intestine discontinues. The so-called spores of E. histolytica were distinguished very definitely from those of E. coli; they were said to consist of spheres of only 3 to 7 µ in diameter, which were surrounded by a double membrane, at first colourless, but becoming a light brownish yellow colour after a few hours, and possessing a protoplasmic content containing chromidia. They were said to arise by fragments of chromatin passing outwards from the nucleus of the amœba into the surrounding cytoplasm (fig. 9, a) and undergoing so marked an increase that finally the whole cytoplasm became filled with chromidia. The remainder of the nucleus underwent degeneration and became extruded. On the surface of the cytoplasm there then arose small protuberances containing chromidia. These processes had been observed in the living organisms. They gradually divided and separated from membranes which later became yellow. The remainder of the amœba perished. Craig[18] had also seen phases of this process of development. It must be remarked that, according to recent researches, these processes of exogenous sporulation are degenerative in character (see p. 41). The small spores may be fungi. The “sporulation” processes are only mentioned here as a warning. They are now only of historic interest. By means of an experiment made on a cat, Schaudinn ascertained that ingestion of permanent cysts, which resist desiccation, is the cause of the infection. The animal took food containing dry fæces with amœba cysts; these fæces came from a patient suffering from amœbic enteritis in China. On the evening of the third day the cat evacuated blood-stained mucous fæces which contained large numbers of typical Entamœba histolytica. On the fourth day after the infection the animal experimented upon died, and the large intestine showed the changes previously stated.

[17] Arb. a. d. kaiserl. Gesundheitsamte, xix, pp, 547–576.

[18] “Life cycle of Amœba coli in Human Body,” American Medicine, 1904, vii, p. 299; viii, p. 185.

E. histolytica also is found in the large intestine. This was originally shown to be the case by Kartulis, and the fact has recently been confirmed from many quarters. It is also present in the metastatic abscesses of which it is the cause (cf. among other authors, Rogers, Brit. Med. Journ., 1902, ii, No. 2,177, p. 844; and 1903, i, No. 2,214, p. 1315).

It should lastly be pointed out in this connection that mixed infections also take place. For instance, in addition to E. histolytica, E. coli, and, under certain circumstances, flagellates may be found together. In the same way E. coli may come under observation even in bacillary dysentery. On the other hand, Schaudinn stated that in cases of dysentery endemic in Istria, Entamœba coli, if it had hitherto been present, disappeared, to return again after recovery from the illness.

(Entamœba tetragena, Viereck, 1907.)

This amœba must now be considered to be a part of the lifecycle of Entamœba histolytica, in fact a very important part of that cycle, especially in its tetranucleate cystic stages.

This organism, the so-called Entamœba tetragena, may occur in the human intestine in cases of amœbic dysentery, especially in mild or chronic cases. It was discovered by Viereck in 1907 in patients suffering from dysentery contracted in Africa. Soon afterwards an independent description was published by Hartmann, who called the amœba E. africana. It was also studied by Bensen and Werner. Recently (1912–13) much work has been published on this amœba by Darling and others; in this way its relationship to Schaudinn’s E. histolytica has been made known.

In general morphology it somewhat resembles Entamœba coli, and its discoverer at first mistook it for a variety of that species. According to Hartmann, a distinct ectoplasm is only clearly visible when a pseudopodium is protruded (fig. 5). The granular endoplasm may contain ingested red blood corpuscles (fig. 6). The large, round nucleus is visible in the fresh state (fig. 8, a). So-called chromidial masses (? crystalloidal substances) may occur in the cytoplasm.

Some investigators, as Hartmann,[19] lay stress on the internal structure of the nucleus (fig. 8, b, c), best seen in preparations fixed wet and stained with iron-hæmatoxylin. The nucleus is limited by a well-marked nuclear membrane, on the inside of which granules or nodules of chromatin may occur. There is a karyosome, which, in successfully stained specimens, shows, at times, a central dot called a centriole. (The nucleus of Entamœba coli does not contain such a centriole.) However, the structure of the nucleus varies at different periods during the life-cycle.

[19] Arch. f. Protistenkunde (1911), xxiv, p. 163.

The diameter of the trophozoites or vegetative forms (fig. 8, a) is variously given as from 20 µ to 40 µ. Multiplication proceeds by binary fission and also by schizogony into four merozoites.[20]

[20] See Darling, 1913, Arch. Intern. Med., vol. ii, pl. i, fig. 3.

Reproduction takes place by endogenous encystment (fig. 9, d-f), which is preceded by nuclear division into two, reduction and then autogamy. The interpretation of the latter phenomenon as autogamy is disputed by some authors. The round cysts, which may measure 12 µ to 15 µ in diameter, contain four nuclei, together with darkly staining masses of various shapes, the so-called “chromidial blocks” (fig. 9, f). The cyst-wall of E. histolytica (tetragena) is thinner than that of E. coli, and the diameter of the cyst is rather less. E. histolytica has not yet been cultivated.

Infection in man occurs by way of the mouth by the ingestion of cysts. A patient showing acute symptoms of dysentery is not usually infective, for he is merely harbouring the large trophozoites, which, by experiment, have been shown not to be infective to animals (kittens) when administered by the mouth. The stools of recovered patients may still contain cysts, and they may thus act as cyst-carriers or reservoirs of disease by infecting water and soil. The stools of such cyst-carriers are often solid, and so cysts of E. histolytica (tetragena) are easily overlooked. Mathis (1913)[21] points out that healthy carriers of E. histolytica may be found; 8 per cent. of the natives of Tonkin examined by him were healthy carriers of cysts.

[21] Bull. Soc. Med. et Chirurg. Indo-Chine, iv, p. 474.

In return cases, or prolonged untreated cases of entamœbic dysentery, a generation of smaller trophozoites is associated with, or replaces the larger ones. In stools they are frequently refractile and consequently stain slowly intra vitam. These trophozoites are the “smaller, senile, or pre-cyst generation” of Darling. This pre-cyst generation is characterized by the presence of blocks of crystalloidal substance in the cytoplasm, and by the possession of a prominent, densely stainable karyosome. Darling believes this generation to be the same as that described by Elmassian as Entamœba minuta.[22]

[22] Centralbl. f. Bakter., Orig., lii, p. 335.

Walker,[23] Darling,[24] Wenyon[25] and others believe that Entamœba histolytica, which was only seen by Schaudinn in a single case, that of a Chinaman, is really E. tetragena. Darling states that if the published illustrations of E. histolytica and of E. tetragena are collected from the literature and compared, it will be seen that the writers have been calling E. histolytica the large trophozoites seen in dysenteric stools. These large trophozoites frequently display no karyosome, but they can be demonstrated as E. tetragena by animal inoculation, or by the history of the case. On the other hand, the illustrations of E. tetragena show that the authors have been dealing with the small generation or reduced forms (“E. minuta”), which are the direct descendants of the large trophozoites. If kittens are inoculated rectally with dysenteric material containing large trophozoites, the strain may be carried in successive kittens for four to six transfers. If, on the other hand, kittens are inoculated rectally with small trophozoites of the pre-cyst generation, the transmission cannot be carried through more than one or two kittens. Wenyon has succeeded in maintaining E. tetragena in kittens for several generations.

[23] Philip. Journ. Sc. (1911), B, vi, p. 259.

[24] Annals Trop. Med. and Parasitol. (1913), vii, p. 321.

[25] Brit. Med. Journ., Nov. 15, 1913, p. 1287, and Journ. Lond. School Trop. Med., ii, p. 27.

In some of the preparations from the last remove, pathological forms of the trophozoites may be seen. These show abnormal forms of budding, especially peripherally, such as have been described by Schaudinn and by Craig as characteristic of E. histolytica. Schaudinn’s small peripheral, exogenous buds and cysts are thus explained. Craig has latterly changed his views.

Further, Darling states that tetragena cysts fed by the mouth to kittens produce bowel lesions in which trophozoites having the characters of E. tetragena, E. histolytica and E. nipponica (Koidzumi) occur.

In view of the work of recent observers, the peculiar exogenous encystment which Schaudinn made characteristic of Entamœba histolytica has been shown to be due to degenerative changes in senile races of the amœba. E. histolytica and E. tetragena are one and the same species, and its trophozoite is subject to variation. According to some observers the histolytica type of nucleus--described by Schaudinn as being poor in chromatin and not easily seen in the fresh state--occurs frequently in patients with severe symptoms of dysentery; on the other hand, the tetragena type of nucleus--round and easily seen in the fresh state--may occur in cases presenting slight dysenteric symptoms. Intermediate types of nuclei are seen. The name of this species, the principal pathogenic amœba of man, must then be E. histolytica by priority. The cystic stages of E. histolytica are those first recorded by Viereck and formerly described as E. tetragena. The geographical distribution of E. histolytica is wide.

*Noc’s Entamœba* (1909).

A species of Entamœba was cultivated by Noc[26] in 1909 from cysts derived from liver abscesses, from dysenteric stools and from the water supply of Saigon, Cochin China. He cultivated it in association with bacteria. It is pathogenic. It has been considered allied to E. histolytica, and shows internal segmentation or schizogony. It exhibits polymorphism. This amœba has been found by Greig and Wells (1911) in cases of dysentery in India. It is an important organism and requires further investigation.

[26] Noc, F. (1909), Ann. Inst. Pasteur, xxiii, p. 177.

Certain other Entamœbæ[27] have been described at various times from the intestinal tract of man. Probably most, if not all, of these are not good species and in some cases much more information is needed.

[27] See Fantham, H. B. (1911), Annals Trop. Med. and Parasitol., v, p. 111.

Entamœba tropicalis (Lesage, 1908). This parasite is said to be non-pathogenic, and to occur in the intestine of man in the tropics. It has a general resemblance to E. coli, but forms small cysts (6 µ to 10 µ in diameter). The nucleus of the cyst is said to break up into a variable number of daughter nuclei, from three to thirteen having been noted. Lesage states that it is culturable in symbiosis with bacteria. It is probably a variety of E. coli, if not a cultural amœba.

Entamœba hominis (Walker, 1908) has a diameter of 6 µ to 15 µ. A contractile vacuole is present. Encystment is total, and small cysts are formed. It is culturable. The original strain, now lost, was obtained from an autopsy in Boston Hospital. This organism is probably a cultural amœba.

Entamœba phagocytoides (Gauducheau, 1908). This parasite was discovered in a case of dysentery at Hanoi, Indo-China. The amœba is small, 2 µ to 15 µ in diameter. It is active. It ingests bacteria and red blood corpuscles, while peculiar spirilla-like bodies are found in its cytoplasm. It multiplies by binary and multiple fission. It can be cultivated. More recently (1912) the author appears to consider the amœba to be a stage of a Trichomonas, but abandons the view later (1914). Further researches on this organism are needed.

Entamœba minuta (Elmassian, 1909)[28] was found, in association with E. coli, in a case of chronic dysentery in Paraguay. It resembles E. tetragena but is smaller, rarely exceeding 14 µ in diameter. Schizogony occurs, four merozoites being produced. The encystment is total and endogenous, giving rise to cysts containing four nuclei. This amœba is considered by Darling and others to be the pre-cyst trophozoite stage of E. histolytica (tetragena).

[28] Centralbl. f. Bakter., Orig., lii, p. 335.

Entamœba nipponica (Koidzumi, 1909) was found in the motions of Japanese suffering from dysentery or from diarrhœa, in the former case in company with Entamœba histolytica. Its diameter is 15 µ to 30 µ. The endoplasm is phagocytic for red blood corpuscles. The nucleus is well defined, resembling that of E. coli and of E. tetragena. Multiplication occurs by binary fission and by schizogony. Encystment is total, but has not been completely followed. Darling and others consider that this is an abnormal form of E. histolytica, while Akashi (1913) doubts if it is an amœba at all, but rather is to be regarded as shed epithelial cells.

GENERAL REMARK.--It is now considered by some workers that true Entamœbæ cannot be cultivated on artificial media. Quite recently Williams and Calkins (1913)[29] have somewhat doubted this opinion, and state that certain cultural amœbæ, originally obtained from Musgrave in Manila, exhibit the various morphological variations associated with true entamœbæ of the human digestive tract.

[29] Journ. of Med. Research, xxix, p. 43.

*Entamœba buccalis*, Prowazek, 1904.

The size varies from 6 µ to 32 µ. Ectoplasm is always present; the endoplasm contains numerous food-vacuoles. The nucleus is vesicular, with a greenish tinted membrane which is poor in chromatin. The size of the nucleus is from 1·5 µ to 4·5 µ. A contractile vacuole is not visible. The pseudopodium is broad. It was discovered in the mouths of persons with dental caries at Rovigno and also at Trieste, being most easily found in dense masses of leucocytes, also among leptothrix and spirochæte clusters. It can be easily distinguished from leucocytes by more intense staining with neutral red. Multiplication proceeds by fission. Transmission may take place through the small spherical cysts. This species (fig. 10) has since been observed in Berlin, and is also occasionally found in carcinoma of various regions of the oral cavity. (Leyden and Löwenthal, 1905).

Entamœba buccalis, Prow., is said to be allied to a protozoön which A. Tietze has found either encysted or free in the lumen of the orifice of the parotid gland of an infant aged 4 months. The gland had undergone pathological change, and had therefore been extirpated. The organisms, which were roundish and three to four times the size of the normal epithelial cells of the gland, were without a membrane and possessed a nucleus in which the chromatic substance appeared to be contained in a karyosome. Bass and John’s[30] (Feb. 1915) and Smith, Middleton and Barrett (1914) state that E. buccalis is the cause of pyorrhœa alveolaris.

[30] Journ. Amer. Med. Assoc., lxiv, p. 553.

Entamœba undulans, Aldo Castellani, 1905.

Under this name a protozoön is described which A. Castellani found in addition to Entamœba histolytica and Trichomonas intestinalis in the fæces of an European planter living in Ceylon, who had suffered from amœbic enteritis and liver abscess. The shape of the body was roundish or oval, 25 µ to 30 µ in the greatest diameter. It was without a flagellum, but with an undulating membrane, and capable of protruding a long pseudopodium from different parts of its body at short intervals. The nucleus could not always be recognized in life; it was, however, always demonstrable by staining. One or two contractile vacuoles were present. The protoplasm was finely granular, showing no differentiation into ecto- and endo-plasm. According to Braun, in spite of the author declaring himself expressly against the flagellate nature of the parasite, such a nature may be assumed to be tolerably certain in view of the description and illustration.

It is now considered that Entamœba undulans is a portion of a flagellate, namely, Trichomonas.

*Entamœba kartulisi*, Doflein, 1901.

Doflein gave this name to amœbæ, from 30 µ to 38 µ in diameter, which Kartulis (1893) found on examining the pus of an abscess in the right lower jaw of an Arab, aged 43, and in a portion of bone that had been extracted. The movements of the amœbæ (fig. 11) were more active than those of “dysenteric amœbæ.” Their coarsely granular cytoplasm contained blood and pus corpuscles, and a nucleus was generally only recognizable after staining. Vacuoles were not seen with certainty. Flexner reported upon a similar case, and Kartulis published five additional cases. As in these cases dental caries was present the infection is likely to have proceeded from the oral cavity as a result of the carious teeth. Craig[31] (1911) considers that this parasite is probably identical with Entamœba histolytica.

[31] “The Parasitic Amœbæ of Man,” Lippincott, Philadelphia.

In the literature the following species have been reported as occurring in the oral cavity of man:--

Amœba gingivalis, Gros, 1849. [? identical with Entamœba buccalis.] Amœba buccalis, Sternberg, 1862. Amœba dentalis, Grassi, 1879.

Far too little, however, is known concerning these to regard them as definite species, that is, independent organisms; Grassi thinks it even possible there may have been a confusion in their case with salivary corpuscles. If they really are amœbæ they are all of them probably identical with Entamœba buccalis.

Genus *Paramœba*, Schaudinn, 1896.

Schaudinn established the genus Paramœba for a marine rhizopod which multiplied by division, became encysted at the end of its vegetative life and then segmented into swarm bodies with two flagella. These multiplied by longitudinal fission, and finally passed into the condition of Amœbæ. Whether the human parasite described by C. F. Craig (1906) as *Paramœba hominis.* belonged to this genus was for a time uncertain. It is now placed in a new genus Craigia, Calkins, 1912, since it possesses only one flagellum.[32]

[32] See Craig (1913), Amer. Journ. Trop. Dis. and Prevent. Med., i, p. 351.

In the amœbic stage it is 15 µ to 25 µ in diameter; ecto- and endo-plasm during rest are indistinguishable. The body substance is granular, with a spherical, sharply contoured nucleus and an accessory nuclear body. No vacuoles are present, but occasionally the endoplasm contains red blood corpuscles. The pseudopodia are hyaline, finger- or lobe-shaped, and are protruded either singly or in twos. Multiplication is by binary fission and by the formation of spherical cysts (15 µ to 20 µ in diameter) in which occurs successive division of the nuclei, ultimately forming ten to twelve roundish bodies each of which soon develops a flagellum. The flagellate stages have similarly a spherical shape and attain a diameter of 10 µ to 15 µ. They also occasionally contain red blood corpuscles and pass either directly or after longitudinal division into the amœboid phase.

Craig found these Amœbæ and the flagellate stage belonging to them in six patients in the military hospital at Manila (Philippine Islands), five of whom were suffering from simple diarrhœa whilst the sixth exhibited an amœbic enteritis and contained also Paramœba hominis, with Entamœba histolytica, Schaudinn. In one of the other cases, Trichomonas intestinalis was present.

B. *Amœbæ from other Organs.*

*Entamœba pulmonalis*, Artault, 1898.

Artault[33] discovered a few amœboid forms with nucleus and vacuole in the contents of a lung cavity. In the fresh condition they were distinguishable from leucocytes by their remarkable capacity of light refraction. They were also much slower than the latter in staining with methylene blue or fuchsine. Their movements became more lively in a strong light. Water and other reagents killed them, and then, even when stained, they could not be distinguished from leucocytes. They have also been seen by Brumpt. R. Blanchard found amœbæ which may belong here in the lungs of sheep. A. pulmonalis is perhaps the same as Entamœba buccalis. Smith and Weidman[34] (1910, 1914) described an entamœba, E. mortinatalium, from the lungs and other organs of infants in America.

[33] Arch. de Parasitologie, i, p. 275.

[34] Amer. Journ. Trop. Dis. and Prevent. Med., ii, p. 256.

*Amœba urogenitalis*, Baelz, 1883.

This species was found in masses in the sanguineous urine as well as in the vagina of a patient in Japan, aged 23. Shortly before the death of the patient, which was caused by pulmonary tuberculosis, hæmaturia with severe tenesmus of the bladder had set in. The amœba, which showed great motility, and had a diameter of about 50 µ when quiescent, exhibited a granular cytoplasm and a vesicular nucleus. Baelz is of opinion that these parasites were introduced into the vulva with the water used for washing the parts, and thence had penetrated into the bladder and vagina. Doflein places the organism in the genus Entamœba, and it is perhaps identical with E. histolytica.

Similar cases are also reported (1892–3) by other authors: Jürgens, Kartulis, Posner, and Wijnhoff. Jürgens found small mucous cysts, filled with amœboid bodies, in the bladder of an old woman suffering from chronic cystitis; they were also found in the vagina. The amœba observed by Kartulis in the sanguineous urine of a woman, aged 58, suffering from a tumour of the bladder, measured 12 µ to 20 µ, and exhibited slow movements by protruding short pseudopodia. The vacuoles and nucleus became visible only after staining with methylene blue.

Posner’s case related to a man, aged 37, who had hitherto been quite healthy and had never been out of Berlin. Suddenly, after a rigor, he passed urine tinged with blood. This contained, besides red and white blood corpuscles and hyaline and granular casts, large granular bodies (about 50 µ in length and 28 µ in breadth), which slowly altered their shape, and contained red blood corpuscles in addition to other foreign matter. These bodies exhibited one or several nuclei and some vacuoles. From the course of the disease, which extended over a year, and during which similar attacks recurred, Posner came to the conclusion that the amœbæ which had originally invaded the bladder had penetrated into the pelvis of the kidney, where they probably had settled in a cyst, and thence induced the repeated attacks.

Wijnhoff observed four cases of amœburia in Utrecht.

*Amœba miurai*, Ijima, 1898.

Under this term the author describes protoplasmic bodies which Miura, in Tokyo, found in the serous fluid of a woman, aged 26, who had died from pleuritis and peritonitis endotheliomatosa. Two days before death these same forms had also appeared in the hæmorrhagic fæces of the patient. The bodies were usually spherical or ellipsoidal, and at one pole carried a small protuberance (fig. 12) beset with filamentous short “pseudopodia” (really a pseudopodium covered with cilia). Their size varied between 15 µ and 38 µ. The cytoplasm was finely granular, and no difference was observable in the ecto- and endo-plasm, only the villous appendage was clearer. The cytoplasm contained vacuoles more or less numerous, none of which was contractile. After the addition of acetic acid one to three nuclei could be distinguished, 8 µ to 15 µ in size. Actual movements were not observed. Taking everything into consideration, the independent nature of these bodies is, to say the least, doubtful, although it cannot be denied that they possess a certain similarity to the marine Amœba fluida, Grüber or Greeff, and to a few other species. (It is likely that cells present in serous exudation were mistaken for amœbæ.)

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