LIBRARY OF THE UNIVERSITY OF VIRGINIA FROM THE BOOKS OF Bruce D. ReynoldsINTRODUCTION TO THE STUDY OF ANIMAL PARASITES AND PARASITISM WILLIAM A. RILEY University of Minnesota Copyright 1927 WILLIAM A. RILEY Mimeographed and Printed by EDWARDS BROTHERS ANN ARBOR, MICH.QL 137 RAS \OR7 Copy |--- PREFACE --- This booklet is not intended as a comprehensive text on the subject of parasitology. It is essentially an ex~ pansion and revision of the author's "Notes on Animal Parasites and Parasitism’” published in 1912, presenting the outlines of an elementary and very brief cours? on the subject. While the illustrations are to a consid¢rable degree from the field of human parasitology or from border- line fields, the subject is treated primarily from the biological viewpoint. Any such course ‘must be under heavy ov'igations tw the classic works of Leuckart, Cobbald, Raililety, Blanchard, and Braun, Brumpt and other ciouse.s in the field and to the early work of Stiles, “avd, Ransom, Lav, and their staffs in this country. One of its most im: portant functions is to put the student in touch with current work in the field of animal parasitology. To this end, lists of important journals and comprehensive texts are supplemented by those of various bibliogravhic aids, auch as indices and abstract journals, Owing to limitations of space, the list of special papers is merely suggestive. The articles cited ‘are wide- ly available and in many cases include reviews cf. the literature and bibliographies. Much of the fundamental work appears in foreign publications and, as in all - scientific work, a knowledge of at least French and German is invaluable to the student. It is urged that the op-'.. portuni ty to become acquainted with original rapers treat-. ing of the subject be improved whenever possible. 1698 . ®.INTRODUCTION Povular attitude course. The more graphic aids. GENERAL PART Definitions. tr parasites, Revie parasites, Lif Reproduction. par asites on thei cl At sure Of paras i mination of paras i Jo parasitic infect C Classification, PROTOZOA Class RHIZeroDa: Glass MASTIGOPHORA es cnet aes, Herve tomon e thi es Chilonast ty der Et Why? pie ep ft Kh th SI AS PRS TS towards parasites. Object of the important text-books anc biblio-~ ucture of the paras’ te. Oceurrence ot : oo views regarding the origin of hintory uf parasites, opectit ci ty. ortals of entry to the host. Action: of ir nost. Reaction of the host. Nomen- eis aiseases. Economic value. Deter- ites 1A the iiving host. Sources of ons. Metheds of control. Origin. ‘Endamoebae of man and animals, be. t NO te cia; Trypanosoma: we shmanias Lx$ Glardia, | <4 * Ry oc 99 be }. iS a 3 3 § we tis CO | } 8 te “ee e ig < oO eT ct Re t - G ty cs {8 N ~J Class SPOROZOA Monocystis; tiroplasmna; RICKETTSTA BODIL’ SPIROCHABTA PLATYNELMINTHES Oe et. wet. watt et ‘ " Vr ny iy t Class TREMA TODA Sere ate Mena Monogenea: wee =. : Digenea: See H> O Himérias lsospora; Plasmodium; Sarcocystis SOR VLonorcnhis; Opisthorchis: S; Metagonimus; Clinostomun: Si D . 2 te aeonAD nus; Schistosoma. Larval eeeTABLE OF WORT ED TS (Contd) Page Class CESTODA 65 Monozoa Merozoa: Taénia; Hymenolepis; Dipylidiun; Diphyllobothrium; Echinococcus; Multiceps. NEMATEERLMINTHES 76 Class NEMATODA 76 Key to superfamilies superfamily Ascaroidea w9 Ascaris; Toxacara (Belascaris); Ascaridia; Heterakis, Superfamily Oxyuroidea 82 Enterobius (Oxyuris); Syphacea. superfamily Strongyloidea 83 Necator; ancylostoma; Uncinaria;: Syngamus superfamily Dicctothymoidea 87 = Dioctophyme (ius trongyTus } Superfamily aenneaaae 88 Trichinella;"Ttrichuris; Eucoleus; Hepaticola; Capililaria. Superfamily Spiruroidea 92 Gongylonéma; Habronema; Acuaria. superfamily Filaroidea 93 Pilaria; Loa; Dracunculus; Dirofilaria. Superfamily Rhabdisoidea 96 trongyloides; Rhabddias Sub-class Gordiacea 97 Class ACANTHOCE PHALA 97 HIRUDI NEA 98 BIBLIOGRAPHY 99 1608‘ Fi ss = ii—-_ INTRODUCTION . POPULAR ATTITUDE TOWARDS ANIMAL PARASITES. - To the layman, parasites constitute a group by themselves, few in number and objects of loathing. Until comparatively recent years even Zo- ologists omitted them from discussion. Today the viewpoint is radically changed. Even the average educated person recognizes that there are other parasites than lice or tapeworms, while z0- ologists, medical men and others interested in public health questions recognize thet some of the most important problems in their fields 2re those relating to animal parasites. OURSE. - Primarily, this course is devoted a biological viewpoint - a consid-~ of life histories. we, ALi oO eration of relationships and Methods of control must be based on such studies. Tllustra- tions are afforded oy the successful efforts to control malaria, hookworm disease, and trichinosis which have followed the work- ing out of the life cycle of the causative organisms. Species of economic importance and especially those affect- ing man Will be discussed when they serve for illustrating the voints under consideration. At times a species of no apparent economic importance will be selected because consideration of its life history or habits may best aid in an understanding of those of more specialized forms. The relation of parasites to disease is an important phase of the subject whicn can only bé touched upon. The pathology and therapeutics of parasitism lie in the fieid of medicine. 50 al- so, the wide series of plant parasites, including pacteria, is omitted. THE MORE IMPORTANT TEXT BOOKS AND BIBLIOGRAPHIC AIDS. The most important object of this Introduction is to open wp the field of animal parasitology and to put the student in. touch with what has been done and with-the constantly increasing mew developments. To this end, references to important papers will be given, by author and date, throughout the text. Such of thesé as cannot he included in the limited bibliographies of this text, can be found by the aid of the standard bibliographic aids listed below. In the following lists, the most available satisfac- tory texts are indicated by an +. @ Comprehans*ve Text *Brumpt, E., 1927. Precis de parasitologie. 4 ed., viii + 1452 pp. Preci Paris: Masson et Cie.“Braun, M. und Seifert, 0., 1925-6. Die tierischen Parasiten des Menschen. 6 ed. 2 vols. 1198 pr. (Second volume con- siders clinical and ther rape sutic aspects.) Leipzig: Kabitsch. Carazzi, D. 1922. Parassitologia animale. 2 ed. xi + 467 pp. Milan: Socicta Editrice Libreria. Castellani, A. and Chalmers, A. J., 1919. Manual of tropical medicine. 3 ed. 2436 vp. New York: William Wood and Co. “Chandler, A. Ge. 1926. Animal parasites and human disease. 3 ed. xiii + 573 pp. New York: Nesey anc Sons Davaine, CG. 1860. Traite’ des entozoaires et des maladies vere mineuses de l'homme et Ges animaux conecsticues xix + xcii + S358 pp. Paris: Bailliére et Fils. (A rich atorehouseé of historic interest.) Fantham, H. B., Stephens, J.W.W. and Theobald, F.V., 1916. Animal perasites of man. 900 pp. New York: William Wood and Co. (Based on the 3 ed. of Braun.) lebiger, J., 1923. Die tierischen Parasiten der Haus - und Nutztiere. 2 ed. xvi + 440 pp. Leipzig: Brebmuller. Gedoelst, L., 1911. Synopsis de parasitologie de l'homme et des animaux domestigquss. xx 332 pp. Bruxelles: Lamertin. Leuckart, K.G.F.R., 1886. The parasites of man and the diseases which proceed from them. Trans. ot WaBe Hoyle. xxvi + 771 pp. Edinburgh: Pentland. (A classic, invaluable today for its biological 1 vViewpoins.) #Manson, P., 1925. Tropical diseases. 8 ed., edited by Manson - Bahr. xx + 895 pp. New York: William Wood & CO. Marotel, G. 1926. Parasitologie vétérinaire. Mense, A,.W., Handbuch der Tropenkrankheiten. 3 ed. in course of publication. Leipzig: Barth. | Neumann, L.G., 1892. A treatise on the parasites and parasitic diseases of the domesticated animals. Transl. and edited vy George Fleming. xxiii + 800 pp. London. Neumenn, R.O. and Mayer, M., 1914. Atlas und Leh tierischen Parasiten und ihrer Ubertrager. v vi i col. pls. Munchen: Lehmann. Neveu ~ Lemaire, M., 1912. Parasitologie des animaux domestiques. ii ¢ — pp. Paris: lLamarre et Gie. we ee ee ee ee eee 1921. Précis de rarasitologie humaine. §& ed. vi + “466 pp. Paris: lLamarre. Railliet, A., 1895. Traitd de zoolorsie medicale et agricole. 2ed. xv +1305 pp. Paris: Asselin & Houzeau. Underhill, B.M., 1920, Parasites and varasitosis of domestic animals. xix + S79 pp. New York: Macmillan. Verdun, P. et Mandoul, A.H., 1924. Précis de parasitologie humaine. S ed. vi +:957 op. Paris: Doin. PAC UN i x TOUE a Valuable information regarding tee s often to be Oob-~ tained from svecial monographs. The following handbooks are con- venient for ready reference. L608.5 . Braun, M. and Lithe, 1910. A handbook of practical parasitology. ingl. transl. by Linda Forster. vil + 208 pp. New York: William Wood & Co. . Daniels, C. W. and Newham, H. B. 1929. Laboratory Svucies in tropical medicine. 5 ed. xiii + 576. London: gohn Bale, Sons & Danielsson. — . #Heener, R. W., Cort, “. W., and Raot, F. M., 1923. Outlines of me@ical zoology. xv +175 op, New York: Macmillan. | #Langeron, M., 1925. Précis de micrgscopice. 4 ed. Xv + 1034 pp. Paris: Masson et Cis. ae Langeron, M. et Rondeau ou Noyer, My, A9G6 » Coprologie microscopigque. i126 pp. Paris: Masson et Cie. Stitt, E. R., 1925. Practical vaeteriology, blood work, and animal parasitology. 7 ed. xv + 766 pp. Philade Lphia: Blakiston & Co. PERIODICALS Meny of the most important contributions dealing with parasites apoeer in periodicals deveted to gen mneral zoology or to human ov veterinary medicine. The fqllowing journals are more svecifically in the field of parasitolory: - “ American journal of tropical medicime. Vol. 1, 1921. Baltimore. Anneles de parasitologie humaine et comparée. Vol. 1, 1922 ee Paris. Annals of tropical medicine and varasitology. Vol. l, 1907 - Liveroool, Archiv fur Naturgeschichte, Vol. 1, 1855 - . Archiv fur Schiffs - und TPronen - Hygiene. Vol. 1 1897 + Leipzic. Archives de parasitologie, Vol. 1, 1898 - Paris.’ Centralblatt fur Bakterliologie, Parasitenkunds, und Infektions-krankheiten, Vol. es L887 - Jena. . Journal of Helminthology, Vol. 1, ive2 - London. Journal of Parasitology, Vol, 1 1914 - Urbana, Til. Parasitology. Vol. 1, 1908 » QGambridge. Société de la pathologie exotique. Bulletin. Vol. 1, 1908 - Paris. 3 * B Abstract Journals Abstracts of bacteriology. Vol. 1, 1917 - Baltimore. *Biological abstracts. Vol, 1, 1926 « Philadelphia. uCentrelblatt fir Bakte riologis, Parasitenkunde, und * ““Infektions- krankheiten, Vol. 4, 1887 « Tena. (Beginning with vol. 3], 1902, the abstracts are published as a separate. vart. j Experiment station record. Vol. 1, 1889 - Washington. 0 1608 PERE rereBein sInstitut Pasteur. Bulletin.” Vol. 1,1903 - Paris. Revue générale de medecine yeterineire. Vol. i, 1903 - Toulouse. “Review of applied entomology. Series B. Medical ana ' Veterinary. Yol.1, i916 - London. Review of bacteriology, protozoology, and general parasitology. “Vol. 1, 1912 ~- London. - #Tropical.diseases bulletin. Vol. 1, 1912 - London. Tropical veterinary bulletin. Vol. 1, 1912 - London. Indexes Agricultural index. Vol. 1, 1916 - New York. Bibliographia zoologica. Vol. 1, 1896 - Leipzig. Concilium bibliographicum (cards) 1896 - Zurich. Index + catalogue of medical and veterinary zoology. Authors. 1902 - 1912 - Washington. Subjects: -Trematoda 1908; Cestoda 1912; Roundworms 1918 Protozoa of man 1925. Index = catalogue of the Surgeon General's Library. 1880 - Washington. S Index médicus. Vol. 1, 1879 - . Tinstow, 0. von. 1878. Compendium der Helminthologie. Ein Verzeichniss der bekannten Heliinthen die frei | oder in thierischen KUrper leben, geordnet nach ihren Wohnthieren, unter Angabe der Organe, in denen sie gefunden sind, und mit Beiflgung der Litteraturquellien. xxii + 382 pp. Hanover. | 1889. Nachtrag - Die Litteratur der Jahre 1878 - 1889. xvi + 151 pp. - Quarterly cumulative index to current medical literature. Vol. 1, 1916 ~- Chicago. | Royal society of London. Cataiogue of scientific papers, 1800 - 1900. Vol. 1, 1867 - London. Zoological record. Vol. 1, 1864 - London. 16085 GENERAL PART Definitions PARASITE. - The term "“nerasite” is not readily defined. While ea often given as “An organism which lives at the expense a another", this definit ion is applicable to @ pr nedatory species, or, in its broadest sense, to all living organisms. For our purposes we may say:- A parasite - 48 an organism which, during the whole or a part of its fife, lives on, “Gr in, in, the bory of another ¢ Organism, of different species, from wonton 2G. obtains its sustenance. PARASITISM, then, is “the condition of life normal and necessary to an organism which feeds at the expense of another, lied the host, without destroying it, as does the predator its prey." Illustrations of various degrees of parasitism are afforded by the malarial parasite which passes its entire existence in some other organism; the bot-fly which is parasitic only in the larval stage, in the stomach of the horse; the flea which feeds on its host only as an adult, or the tapevorm “hich is parasitic through- out its cycle, except | for a vortion of the embryonic stage. PREDATORY SPECIES differ in thet they live on organisms smaller than themselves, and immediately kill their prey. There 4s not a’ sharp line to be drawn between the predaccous and the par- asitic habit. Some forms exhibit both relationships, or, for ¢x- ample, lecches which may kill and fecd on smaller invertebrates, but are parasitic on the highcr animals. SAPROZOA (loosely, seprophytes) are eee from par- asites in that they live on decaying organic matter. Here, too, it is impossible to draw a hard and fast line and there is much evidence that one of the lines of development of the parasitic habit is through these forms. : Parasitism involves a dsfinite and essential: relation bc- tween individuals of two species. Such a relationship is symbiosis. SYMBIOSIS (syn=together; bios=life) in the broad sense of the word, is the living together in definite and constant relation- ship, of two dissimilar organisms. Mutualism is that symbiotic relationship in which two svecies living together mutually and permanently, help and support one another. Examples, the lichen, an association of fungus and an alga. Hydra viridis, Gonvoluta, (a turbellarian worm), and 16086 numerous other forms which owe their green color to unicellular algae, (Zoochlorellae). This is often referred to as typical symbiosis, the sense in which that word was first used by the botanist de Bary, 1879. (Keeble and Gamble, 1907; Keeble, 1910.) Commensalism is the living together of tvo species as messmates, one party, only, profiting but the other not disadvan- taged. Ex., Endamoeba coli in the human intestine; Pinnotherus, a pea-crab, with the oyster. | ee FORMS OF PARASITISM - On the basis of position we may dis- tinguish: - ; I. Ectoparasites, or cendozoa, which live on the exterior of their host or, moré rarely, in cavities which communicate freely with the surface. Ex., various species of lice, ticks, the itch mites and the hair follicle mites. II. Endoparasites, those which live within the internal organs, - as do tapeworms, blood parasites and the like. Intergrading conditions are represented by the above-mentioned mites which burrow into the skin. "aes On the temporal basis parasites may be grouped as:- I. Temporary parasites, those which visit the host only at in- tervals. EX., mosquito, chicken mite, Argasid ticks. II. Stationary parasites, those which remain on or in the host for considerable periods of time. Of these we may have periodic parasites such as bot-flies, op ichneumon flies, parasitic in only a Stage of the life cycle; and permanent parasites such as trichina, parasitic for life. Incidental psrasites are those which under natural conditions are occasionally found in unusual hosts. Examples: the double pored tapeworm,binnviidium caninum of the dog, in man; a mouse nematode, Syphacia Obvelsta, in man. Facultative parasites are livin? but which arc abic te exis introduced into the body of an larvae of blow-flies. no when accidentally t rmally free- i:s e xh other animal. Ex cheese skipvers, Spurious parasites are objects which have bcen mistaken as parasites and sometimes even been given specific names. Ex., plant hairs, bits of gristic, connective tissue, fungus spores, pollen grains, etc. Grosser illustrations are reports of frogs and lizards reported to have been voided by humans. . 1608ry STRUCTURE OF THE. PARASITE te ee em SNe shown tha morvholor ws cr 2 2 @ ae Adepta i¢ biological. Morphological adaotation. - With all the variety tions to environment are nowhere more strikingly te ase of parasites. ‘hese adaptations ere both of struce- ture, there are you certain Characteristic modifications which accompany parasitic lite. As Cau liery 1919, has well where else does structure avpear so sharply outlined 2a + — UN Ow s modeled by the kind of life, nor does preadaptation appear lens probable". Numerous illustrations may also be found of convergent evolut ion, Similar structures indevendently developed in widely STOuUdS . +e Morphological adaptations of two general types: separated A. - Degencrations. TIliustrated by the reduction of organs of locomotion, as loss of wings in parasitic insects; and other appendages of crustacea; fusion of body soamonts; “Loss Or cilia. Correlatcd with these reductions are changes in systom. Parasites often exhibit marked reduction of the muscular the nervous System and sensory organs. Extreme cases are illustrated by the loss of the alimentary canal in Cestoda and Acanthoce chala and still more by the changes undergone by various crustaceans parasitic on fish. B. ~ Neoformations. Structures may be newly de the form of Organs of a peaehnont as, modified tarsi inhabiting mites and lice; sucke 13 and hooks of tapow reloped in of heir orms and flukes. bauivalent st egecuncs are tc be seén in protozoan parasites. Adaptations in soxual organs sre illustrated by hermaphroditic forms. Biological adaptations. - Of the various biologi cal adaptations Shown by parasitic forms, one of the most intcresting is that of specificity in rela tion to their hosts, a topic to be discussed later. Another is that tvpe of tropism dosignated by Brumpt, as.a specific histotropism, which directs the entering parasite to a particular tissue or organ of the host. If the choice is iess limited, the term indif fferent Histotropism is applied. fy ro TH. PAYOR ™ A Tt is Ci CCURRENCH OF PARASITES Practically all animals, from amoeba with parasites in its nucleus and its body protoplasm, to ma are subject Leuckart, '76, lists 33 animal parasites of man, now known. The dog is known to harbor some 200 species, about loo. L606 tO. attack, over 500 are the cat8 Hyperparasitism. - Parasites themselves may be infected by other parasitic Species which are then known as hyperperasites. Examples are afforded by a protozoon, Nosema heiminthorum Ln the tapeworm, Moniezia expansa, and numerous illustrations from insect parasites. these forms by attacking the parasites of in- jurious species, themselves become injurious from the viewpoint of man. Dean Swift, nearly two centuries ago, expressed a broader truth than he suspected when he wrote:- "So, naturalists observe, a flea Has smaller fleas that on him prey And these have smaller still to bite'cn, And so proceed, ad infinitum." Numbers which may occur in a single host. - This is devend- ent on the species of parasitc. There is rarely present more than one of the pork tapeworm, Taenia solium, or of the beef tape- worm, Taenia saginata in man. On the other hand, upwards of a hundred of the still larger fish tapeworm, Diphyllobothrium latum ave been noted. It is not wncommon to find over a thousand tapeworms in a chicken. Over six thousand hookworms have becn recovered from a single patient. Of larval forms it has been estimated that in a severe case of trichinosis over sixty million of the worms may be present. Of Protozoa, the numbers are beyond conception - it has been conservatively estimated that at least one hundred and fifty million malarial parasites must be present before the clinical symptoms of the discase are manifscst. | Concurrent infection by two or more specics in the same individual 18 very common. For man, as many =s five different species of intestinal worms at a time have been reported (Riley, 1912). Location within the host. - As might be expected, the larger number Of species Occur On the surface of their host, or in cav- ities opening to the surface, such as the alimentary canal, res- piratory, and urinogenital passages. Other species are found in muscles, connective tissue, nervous tissue, the blood and the lymoh. They may live free within a cavity, or in cells, and even in cell nuclei, as for example, Sphacrita endamoebae Becker, 1926, or Nuclecphaga amoebae Dangeard, l8Yo. EARLY VIEWS REGARDING THE ORIGIN OF PARASITES. The theory of abiogenesis, or spontaneous generation, ac- cording to which living organisms originate from non-living mat- ter was taught by the early zoologists and in some forms -is 16089 popularly believed even today. The work of Redi, in 1668, on the origin of maggots in meat conclusively demolished the theory in so far as it concerned the non-microscopic free-living forms, but zoologists were long unable to account for the presence of perasites in the interior of the pody. Until well into the 19th century it was believed that tapeworms originated from the mucous of the intestine, or from partially digested food, and that itch mites in the skin of man were the result of “bad blood". The theory of the inheritance of parasites was also invoked to ¢ex- plain their presonce.e The theory of biogenesis, or development from preexisting living forms was extended to the parasites by the beginning of the T9th century, but most authoritics then be jeved that such forms originated from free-living protozoa, and other free-living forms,- the theory of hetcrogenesis, or chence development from wholly different specics. ee . The development of the: experimentcl method of study furnish- ed the Key to tho problem. Feeding experiments with tapeworms by Kuchenmeister, 1851; followed by similar work by Van Beneden, Leuckart, Cobbald and many others, opened up the whole field of modern parasitology. LIFE HISTORY OF THE PARASITE "Tf we only kmow concerning a certain animal that it is a parasitc, we know but little; thoroughiy to understand its his- tory, we must follow out all the scparate stages and conditions of its existence, and cspecially the circumstances under which it becomes a parasite.” - Leuckart, '36 p. 42. 3 As regards relation to host parasites may be grouped as3- TA) WMonoxenous parasites (monos=one; xenas=host), such as require only one host to complete their development. As Brumpt has emphasized, these are of human parasites the cosmopolitan forms, since they have accompanied man everywhere that the tom= porature is sufficient to assure their devolopment. : (B) Heteroxenous parasites (hetcros=different; xenas=host), such as pass different stages of their lives in different hosts, - usually belonging to different genera, and often widely distinct. Their distribution usually depends on the distribution of their intermediate hosts. : Intermediate host. - This term is applied to the organism which supports the asexual or immature form of the parasite. It is somctimes called the secondary host. Definitive host. - The hosts which supports the sexually ERAT ON eR ee . . e mature torm 18 known as the dcfinitive or primary host. 160810 Rssential host. - This term is a convenient one, which is non-commital as to the particular stage of the parasite concerned. VO Method of transfer. - In many cases, the transfer of the « parasite to the host is passive, the embryo being taken with food or drink, or being injectea with the saliva of a blood-sucking temporary parasite. The first type is known as: the ingestivé method, the second, the-inoculative. Of the latter type, are casés in which the organisms are found in.the excrement or body fluids of the arthropod host, and are inoculated by the scratching of the victim. Contrasted with the passive method is the active transfer as illustrated by larval hookworms boring into the skin. Alternation of generations, or metagenesis, the development ; of one or more asexual generations followed by a sexual generation, 4g very common among parasites, (ex., malarial parasite in man aud « in Anopheles mosquite). 3 ; , Nv SPECIFICITY OF PARASITES oF + Many species of parasites are limited, normally, to a single species of host, that is, they exhibit host specificity. So common “is this that there is a tendency on the part of Inexperienced workers to determine their specimens by reference to a host index. . 3 However, the immature Echinococcus, or hydatid tapeworm, is known to develop in over forty different mammals; trichinae thrive eoual- ly well in man, pig, rat and a wide series of animals, and many similar illustrations could be cited. 2 7 More puzzling are cases where morphological distinctions are | lacking, or within the range of variability, but where experimental | transfers from one host to the other have failed. In an increasing | number of such cases, as for example, that of Hymenolepis nana, the dwarf tapeworm of man and the rat and mouse, repeated attempts —~ have yielded occasional positive results. pe 1 In a valuable discussion of the host specificity in both plai » and animals, Sandground 1925 (Jour. Parasitology, 12:68) says, "{t seems that the restriction of a population of parasites to a particular host species for a great number of generations leads to a special adaptation towards this species and 4 corresponding loss of adaptability towards other hosts. This loss may only be | temporary but if the parasite be restricted for a sufficient number | of generations the probabilities are. that the loss will be per- MANENG. .. see ecee sor enrccsencrsrceress«' The situation among nematode ~ parasites of animals is, I believe, closely analogous. to that which obtains among nematode plant parasites." See, also, the very suggestive paper by Chandler, 1923. 1608ae ae THE REPRODUCTION OF PARAST TES The complicated life cycle of many parasites is a dis- advantage in thet it enornously lessens the chances of the species perpetuating itself. This handicap is met in various ways, of which the following will serve as illustrations. Great fertility is typical. - 1t is es stimated that Taenia saginata, the veer tapeworm 0 orm Of man, produces 150,000, 000 eggs per year, about three hundred times its body weight. A single female of the hookworm. Necator americanus, discharges some 9000 eggs daily (Stoll, 1925) whi le the output of the other common hockworm of man is some 45000 eggs per day (Sweet, 1924). The usual method of diagnosing the presence of intestinal and liver parasites by microscope examination of minute random sampling of the feces, is based on the enormous production of eggs and of cysts by the various species present. Other parasites, notably certain insects, and the hydated tapeworm, Eehinococcus granulosus exhibit polyembryony, or the develop- ment of many individ Tuais from a single Gea. Resistance of various developme ntal stages to unfavorable conditions. - various parasitic protozoa have developed a featstant spore stage in which they are protected when out of their host; tapeworms, whipworms, ascarids and many other forms have thick-shelled, resistant eggs. Those of Ascaris lumbricoides of man have been preserved in viable form in earth for five years, or, they will remain alive in strong formalin and other chemical solutions for months (Yoshida, 1920). Eggs of a common roundworm of chickens will survive for upwards of a year in freezing tem-~ peratures (Riley and James, 1921). Illustrations of this nature show the futility of the attempted soil sterilization by sprink- ling it with weak solutions of corrosive sublimate, or of sulphuric acid. Larval hookworms have been kept alive in the soil for months. Dufour (1833) kept bed-bugs for a year in a closed vial, without food. Argas miniatus, a chicken tick, has been kept similarly in our laboratory for four years, and then was acci- dently killed. Herma phroditism is commonly met with in parasites, thus providing for the perpetuation of the Species by a singic individual. eee mer eee PORTALS OF ENTRY TO THE. HOST The ways in which the parasites gain entrance to their host are variable. The chief portals of entry are the;:- 160812 1. - Alimentary canal, with food or drink, or from soiled fingers, toys, fondling of enimal pets, and gsophagy, or the dirt-eating habit. This is the ingestive metnod. ? ; 2. - Skin, by active penetration, as sarcoptic mites, hookworm. larvaé, Cereariae of blood flukes; or, secondarily, by scratch- _ ing of the patient as in the case of the spirochactes of relaps-~- ing fever. 3. - Blood, through the bites of ectoparasites, - ticks and Rocky Mountain spotted fever; mosquitoes and malaria. In contrast to the ingestive method this is known as the inoculative. 4. - Prenatal infections are known to occur by the hookworms of man and animals; ascarid worms; malaria and numerous other In- Stances among the Protozoa. 5. - Other exceptional vortals are the resoiratory passages, urinogenital apoaratus, the ear, and the conjunctivia. ACTION OF PARASITES ON THEIR HOST The history of parasitology shows extremely divergent views as to the sxtent of the injuries caused by parasites. Early opinions attributed most of the ills of man to helminths. The work of Pasteur and Koch served to focus the attention of medical men everywhere on bacteria and for years the tendency was to attribute all diseases to these organisms. Renewed interest in the grosser parasites followed the studies on trichina and on the tunnel disease which Perroncito, 1880, showed to be due to hook- worm infection. Still later came the recognition of the important role played by protozoan parasites and by the arthropods as carriers of disease. Today it is universally recognized by Students of the subject that animal parasites must be reckoned with as causes of some of the most devastating diseases of man and animals.. The action of the parasite is dependent not only upon the species concerned but also upon the age, the physiological condition and cven the racial characters of the host. Parasitism may be latent, the organisms remaining for long pian mma periods without manifesting themselves and suddenly, under some peculiar condition of the host becoming active. Such, for in- stance, is the case with malarial or amoebic dysentery infections. Of the various ways in which the parasite may affect the host, we may note; - : 1. = Drain on the nourishment. - While this is popularly overesti- mated, it may be of considerable importance when large numbers of — the parasites are present or when they are vrimarily blood-suckers, 2. - Destruction of tissues. ~ The Texas fever parasite, Babesia bovis, may wreak down aS many as two-thirds of the red blood Cor- puscles of its host; Coccidia destroy the liver cells and the in- testinal epithelia of rabbits; the Giant Kidney Worm, Dioctovohme renalis, renders the kidney of its host a mere shell. 160813 3. - Mechanical disturbances. - These may be by obstruction or py vressure. Of the former, an instance is afforded by the filarial worms which by blocking of the lymph channels cause elephantiasis, or by Ascaris lumbricoides in the gall duct or, in large numbers, cauSing intestinal impaction. The effect of pressure is often very manifest in the cases of the development of hydatid cysts (Echinococcus) in the liver or other organs. 4, - Irritation and inflammation. - The presence of parasites may irritate the tissue and stimulate it to abnormal growth, producing cysts such as those of trichina, or the capsules surrounding cysticerci of various taveworms, or the intestinal nodules produced by roundworms of the genus Oesophagastomum, in sheep, cattle and hogs. Of special significance is the fact that a cancer of the stomach in rats is induced by a roundworm of the genus Gongylonema (Fiebiger, 1915). 5. - Production of centers of infection. - Injury to the skin by biting or piercing forms not infrequently leads to secondary in- fections. Similarly, intestinal parasites may lacerate the mucosa and permit the entrance of typhoid bacilli or other onthogens. The perforation of the intestinal wall by Ascaris often results in peritonitis, while wandering hookworm larvae or treichinae may carry bacteria with them to the inner tissues. 6. - Production of specific poisons. ~ The parasite in its metabo- lism may produce specific poisons which are injurious to the host. Such, for instance, are produced by the malerial parasites, the trypanosome of sleeping sickness, Ascaris, and the fish tapeworm of’ man. . 47, - Nervous reactions. ~ Characteristic nervous symptoms may ac- company certain oarasitic infections as, for example, itching of the nose apparently due to pinworms (Oxyuris); hysterical symp- toms.which have been relieved by discharge of ascarids; resplira- tory disturbances due to the presence of the giant kidney worm in the abdominal cavity, or the intense irritation caused by the presence of the gape-worm in the tracheae of chickens. 8. - Danger from intermittent parasites. - Far from being mere 4an- noyances, intermittent parasites are among the most dangerous of the group, since they often carry and disseminate pathogenic or- GANLsins a : REACTION OF THE HOST TO THE PARASITE oe eS ee (eee teen eee set mee While the parasite is able to injure its host in various ways, there are certain reactions of the infected organism itself which must be considered. This phase of the subject has been elaborated by Brumpt, 1923, who groups the methods of defense as {A) the cellular elements, mobile or fixed, and (B) the proper- ties of the body fluids. A. - Gellular reactions provoked by the parasite. - These may be: in?iammatory, motadlastic, hyperplastic, end neoplastic. 1608EE terete cose nm ns 14 Inflammation is marked by more or less abundant exudation of blood serum, by the collecting of various types of white blood cells, or leucocytes, and often by the formation of a connective tissue capsule about the parasite; 4s illustrated by the larvae of tapeworms. Metaplastic changes are characterized by the metamorphosis, or change, of One tissue into another. Brumpt cites as an illus- tration the transformation of the normal cylindrical epithelium of the bronchi into a stratified pavement epithelium in cases of pulmonary infection by flukes of the genus Paragonimus » Hyperplastic changes are those in which there is an ab- normal multiplication of the tissue elements, such as is found in the epithelium of the gall ducts in trematode infections of the Liver. : Neoplastic reactions are those resulting in tumors, or morbid growth more or less distinct histologically from the tissue in which it oceurs. Most of the so-called tumors caused by parasites are not true tumors but are connective tissue growths more proper- ly classified as types of inflamation. B. ~ Humoral reactions. - The presence of parasites in the pody of an animal tends to develop in its blood serum, or other pody fluids, certain specific substances, or properties antagonis- tic te the invading organism. These substances are called antibodies and the foreign protein, in this case the parasite or its products, is called the antigen. In many cases and, particu- larly, if the parasite is not normal to the particular animal, these antibodies suffice to destroy it. On the other hand, in rare cases, certain of the substances may even sensitize the host and then produce serious effects or death, from anaphylactic shock. An illustration is afforded by Hadwen's, 1917 studies on the effect of improper removal of grubs, or warbles, from cattle. NOMENCLATUR@ OF PARASITIC DISEASES ener Parasitic infections are designated technically by the generic name of the causative organism, with the suffix iasis or esis, as, taeniasis, ascariasis, trichinosis, pediculosis. Such names do not necessarily follow changes in the zoologi- cal nomenclature. For example, the term cistomiasis is often re- tained for fluke infections, although the old genus Distoma has been broken uv into a large number of genera. 160815 ECONOMIC VALUE OF PARASITES From the viewpoint of man, not all parasites are noxious, since they may be important factors in the control of injuri- ous species. This has proved of special significance in the control of certain insect pests of our forest and fruit trees. Federal and State authorities have cooperated in the introduc- tion of parasites of imported pests and in some cases have attained spectacular success (see Howard; 1927). In this connection it should be noted again that hyperpar-~ asites attacking these beneficial forms are to be classed, as pests. DETERMINATION OF PARASITES IN THE LIVING HOST References: - Stiles, 1907; Brumpt, 1922; Hall 1911; Hegner, Cort and Root, 1922. Ectoparasites. - The diagnosis of external parasitism is usually Simple, being a question of finding the organism. How- ever, the habits of the various parasites must be taken into consideration as, for example, those of the body lice, which hide in the seams of clothing when not feeding, or those of various temporary parasites which leave their host altogether when they have fed. Moreover, as Styles has emphasized, thei» presence may be unsuspected because apparently incompatable with the habits of the patient. Not infrequently the secondary infections complicate the diagnosis. Endoparasites. - The chief methods of diagnosis of internal parasites are as follows:- | 1. - Accidental expulsion. - Until very recent years this was the chief Way in whith thé presence of the grosser parasites came to the attention of the physician or the owner of animals. 2, - Feces examination. - The chief method of the determination of intestinal and Tiver parasites is the microscopic examination of minute samples of feces, for protozoa and their cysts, and eges or larvae of helminths. The sample is usually taken at random but, in the case of protozoal infections it is often advantageous to select bits of mucus for special examination. In some cases concentration methods such as sedimenting and. sieving, centrifuging, or flotation in concentrated salt solution are necessary. 3, - Sputum. - This may reveal the presence of lung and tracheal parasites, such as lung flukes of the genus Paragonimus, in man, pig, cats, dogs; or nematodes in the trachea of cats or silver fox. 1608 Se16 4. = Urine. - For evidence of kidney, bladder, and certain plood flukes. Examples, the flagellate protozoon Trichomonas or, rarely, amoebae; eggs of the giant kidney. worm, Dioctophyme renalis, or of the blood fluke Schistosoma haematobiun. 5. - Blood. - This may not only reveal blood parasites, such as malaria, trypanosomes, and filarial worms, but through the abnor-~ mal abundance of a special type of leucocytes, the eosinophile corpuscles, may indicate the presence of certain parasites, notably trichinae, elsewhere in the body. 6. - Biopsy, or the removal of tissue from the living host. The method of "harpooning” or removing a bit of muscle is sometimes of value in diagnosing trichinosis. 7, - Culture methods. - The use of cultural methods has been ef- fectivély applied to the diagnosis of intestinal amoebae, and .- flagellates, trypanosomes, and some of the intestinal nematodes. A special type of cultural method is that of using the arthropod host instead of an artificial’ medium. This has been designated xenodiagnosis by Brumpt, 1914, who has applied it especially to the study of trypanosomes. 8. - Serum reactions. ~ The most widely used of these tests is the Wasserman test for syphilis, but similar methods have been used in the diagnosis of various animal parasites, notably the echinococcus or hydatid cysts (Magath, 1921}. : 9. ~ Clinical symptoms. - These are usually vague and little to be relied on. in some cases they are sufficient for tentative diagnosis. SOURCES OF PARASITIC INFECTIONS As will be brought out clearly in the discussion of various parasites, the chief sources of infection are: 1, = The ground. - Hookworm and strongyloides larvae; eggs of As- caries, sreesics. and various other nematodes which may remain for months and even for years in viable condition in the soil, 2. ~ Water. = Protozoal cysts; eggs of various helminths; cercar-~ iae of blood flukes; various tapeworm cysts in minute crustaceans which are accidently swallowed with water. | Oo. * Vegetables and fruits served in uncooked condition. These are a special source of danger in countries where human excrement is used as fertilizer. 4, - Other animals:- a. = Which serve as food: - pig and trichinae, or pork tapeworm; cattle and tapeworm: fish and fluke infections. b. ~- Pets and companions. - Double pored tapeworm of dogs and man; Echinococcus tapeworm; mange of cats; fleas of cats and dogs. — c. - Ectoparasites transmitting parasites by their bites, or, by infective excrement, or body fluids. d. - Humans, from contact infections. 16081? METHODS OF CONTROL OF PARASITES Disappointment and failure have followed all attempts to combat widely distributed parasites of men and animals by treat- ment measures. In such campaigns preventive measures must be the main reliance and these must be based on a thorough knowledge of the life history and ecology of the parasite concerned. The chief preventive measures may be grouped as follows:- 1. - SANITARY METHODS. ~ Cleanliness, both personal and civic, constitutes one of the important safeguards against parasitic infections. This involves proper methods of sewage disposal sO as to avoid contamination of sofl, food, and water; fly — control to protect food and drink from direct carriage Of. in- _féetions; and the proper control of animal pets, since several important parasitic diseasés Of man and stilT more of domesti- cated animals are contracted from dogs and cats. Meat inspection, not only in the large packing houses but in local slaughter houses, plays an important role in the preven- tion of human infections, and the proper disposal of slaughter-- house offal which is thus insured, is a very important means of preveriting further animal infections with such parasites as -trichinae, hydatid tapeworm, and others. es @» = HEAT STERILIZATION through cooking of foods is one of the ~ most important methods of avoidance of such parasites as trichinae,. the beef tapeworm, and of various protozoal parasites. The oft- recommended dipping in solution of calcium chloride of fruits and vegetables which are to be eaten raw is useless. Much safer is ° dipping for ten séconds in boiling water, or water which remains at 80 CG. (176 F.), as recommended by Mills, Bartlett, and Kessler, 1925, Similarly, water may be rendered safe by boiling. Oe © REFRIGERATION of meats, under proper control, is sufficient to kill various cysts of parasitic worms. The régulations of the federal Bureau of Animal Industry permit beef lightly infected by cysts of Taenia saginata passed as food after 6 days in cold storage. 4. ~- DESTRUCTION OF ESSENTIAL HOSTS. - In many cases this 15 a feasible and fundamentally important method of control of parasites. Tilustrations are afforded by the destruction of certain species of mosquitoes in anti-malarial work, and of other species, still. in combatting yellow fever; the killing of stray dogs and coyotes forms an important line of attack against the serious gid tapeworm of sheep, or against the hydatid tapeworm. The Bureau of Animal _ Industry requires that all collie or sheep dogs imported into this country be held in quarantine pending the results of fecal examina- tion for tapeworms. oes L60818 ORIGIN OF PARASITES Parasitic habit not a basis of classification. - It was long supposed that parasites constituted a natural group, the older workers classing various endoparasites together as "helminths", Relation of free-living forms. « The close relationship to free-living forms fs readily seen in many of the endoparasitic nematodes and trematodes. In others, such as some of the parasitic crustacea, it is clearly shown by the developmental history. All of the available evidence tends to show that arasitism is an adaptive phenomenon, originating independently un widely different groups. THE CLASSIFICATION OF PARASITES Representative animal parasites will be considered in their z0Ological sequence and the group characteristics will be dis- cussed in that connection. The following list of phyla of the Animal Kingdom summarizes briefly the groups with which we shall be especially concerned. a ao PHYLUM PROTOZOA Animals in which the entire body consists of a single animal cell, Class RHIZOPODA - Protozoa in which the motile organs are pseudopodia. Glass MASTIGOPHORA = Protozoa with an outer colle integument and in which the motile organs are flagella. : Class INFUSORIA - Protozoa with an outer céll-integument and which are always ciliated either through life or in the young condition. ; Class SPOROZOA + Parasitic Protozoa typically without organs Of locomotion, and which reproduce by spore-formation,. Group not a natural one, Class SPIROCHAETA ~ Spiral organisms with flexible slender bodies, diffuse chromatin and active movements often classed with bacteria. Phylum PORIFERA Not discussed in this course. | Phylum COELENTERATA Not discussed in this course. Phylum PLATYHELMINTHES 1608La PHYLUM PLATYHELMINTHES The Platodes or Flat-Worms The flat-worms are bilaterally symmetrical animals, which are devoid of true metameric segmentation, and which have no body cavity between the alimentary canal and the integument. There is no blood-vascular system: but there is an excretory (water-vascular) system. The alimentary canal when present has only a single opening, and is much branched. Class TREMATODA - Parasitic flat-worms, without a covering of cilfa In the adult state, with a well-developed digestive ap- paratus, and with the mouth at the cephalic end of the body. The liver-fluke is an example of this class. Class TURBELLARIA ~ Non-parasitic flat-worms, with a ciliated epidermes. Not discussed, ee Class CESTODA - Endo-parasitic flat-worms, without cilia, and without a digestive cavity; usvally becoming segmented by budding. This class includes the tapeworms. Phylum NEMATHELMINTHES The Thread Worms The body is cylindrical, spindle-shaped, or threadlike, un- segmented, and. covered with a thick cuticle; the body cavity is usually spacious. The sexes are usually separate, but hermaphroditic species occur. Yorke and Maplestone recognize two classes of this phylum. Class NEMATODA - With an alimentary canal but without 4 proboscis. Order Eunematoda -' Alimentary canal typically complete and present throughout Iife, body cavity not lined with epithelium, lateral cords present. Familiar examples are Ascaris, Oxyuris, Trichinella. Order Gordiacea - Larval stage parasitic and possessing an alimentary Canal; adults free-living, without an alimentary canal; body cavity lined with an epthelium. To this order belong the "hair-snakes" of the genus Gordius, and related forms. Class ACANTHOCEPHALA ~- Lack alimentary canal; possess a protrusible proboscis which is covered with many rows of recurved hooks. 160820 Phylum ECHINODERMATA Not discussed in this course. Phylum MOLLUSCOIDA Not discussed in this course. Phylum ANNULATA The Syamented Worms Bilaterally symmetrical animals with the body composed of Similar segments or metameres, without jointed legs, and with an alimentary canal furnished with two openings. Only one of the Classes discussed in this course. Class HIRUDINEA - Segments of body marked externally by sec- ondary rings. Each end of the body is furnished with a sucker. The medicinal leech is an example of this class. Phylum ARTHROPODA See Comstock's "Manual for the Study of Insects" and "The Spider Book". , Bilaterally symmetrical animals in which the body is segmented and bears a pair of jointed appendages on each or on some of the segments. Class CRUSTACEA - The members of this class are aquatic Arthropoda, which breathe by true gills. They have two pairs of antennae and at least five pairs of legs. Glass ARACHNIDA - The members of this class are air-breath- ing Arthropods, in which the head and thorax are grown together, forming a cephalothorax; which have four pairs of légs fitted for walking, and which have no feeler-like antennae. To this class belong the spiders, ticks, mites, and others. Order ACARINA - This order includes the mites; these differ from other Arachnida in that the abdomen is fused with the cephalothorax, giving the entire body a more or less saclike appearance. Class MYRIAPODA - This class includes the centipedes and the millipedes, air-breathing Arthropoda in which the thorax and abdomen form a continuous region, with from six to two hundred segments, each bearing a pair of legs. 160821 Class HEXAPODA - Air-breathing Arthropoda, with a distinct head, thorax and abdomen. They have one pair of antennae, three pairs of legs, and usually one or two pairs of wings in the adult state. This class is composed of the different orders of in- sects:- of special significance to the parasitologist are the following: . Order MALLOPHAGA - This order includes the bird lice; these are wingléss parasitic insects, with biting. mouvth~-parts; their metamorphosis is incomplete. Order ANOPLURA - The order Anoplura is a small group, com-, posed of the sucking lice. They are wingless, parasitic insects with piercing and sucking mouth-parts in the form of an invaginat~- ed tube; the thoracic segments are fused, and the legs are fitted for clinging to hairs of the host. Order HEMIPTERA - This order includes the true bugs. The winged mémbers have four wings, but certain species are wingless; the mouth parts are formed for sucking; the metamorphosis is in- complete, Order DIPTERA - This order includes the flies, among which are the mosquitoes, bot-flies, the sheeptick, and many others. The winged members have only two wings; the mouth-parts are formed for sucking; or for piercing and sucking; the metamorpho- Sis is complete. Order SIPHONAPTERA - This order includes the fleas; the mem-. bers of it are practically wingless, the wings being represented Only by minute scaly plates; the mouth-parts are formed for suck- ing; the metamorphosis is complete. Phylum MOLLUSCA Not discussed in this course. Phylum CHORDATA OR VERTEBRATA Not discussed in this course. 160822 SPECIAL PART REPRESENTATIVE PARASITIC PROTOZOA Important General References Butschli, 1880 - 1889; Calkins, 1909, 1926; Craig, 1926; Doflein, 1916; Hartmann, 1921; Hartmann and Schilling, i917; Hegner, 1927; Hegner and Taliaferro, 1925; Minchin, 1912; Noller, 1922; Prowazek, 1911; Wenyon, 1926. | The early microscopists, in their incessant search for new wonders did not fail to note the presence of parasitic Protozoa in the animal body. Thus, Leeuwenhoeck (1632 ~ 1723) studied the intestinal protozoa of frogs and, as Dobell has pointed out, noted the oocysts of the rabbit coccidium and even studied the flagellate, Giardia intestinalis from his own stools. About the middle of the 19th century the presence of amoebae and of the intestinal infusorian Balantidium coli in man was noted, Soon after this time Pasteur was making his famous studies on the nosema disease of silkworms, although he did not recognize the causative organism as a protozoan. : Overshadowed by the rise of bacteriology and by the search for bacteria as the specific cause of all diseases, the signifi- cance Of Protozoa as pathogenic organisms was long overlooked. Indeed, relatively little attention was given them until the beginning of the present century. Now it is well-known that some of the most devastating diseases of man and animals are of protozoal causation. Of the many illustrations there may be cited, malaria, sleeping sick- ness, kala-azar, yellow fever, the Texas fever of cattle, the nosema disease of silkworms. All of the sub-phyla of Protozoa contribute important illustrations of parasitic forms. They inhabit organs, tissues and cells and even the nuclei of cells of their varied hosts. Their adaptations, both morphological and biological are comparable to those of other parasitic Groups. CLASSIFICATION Without entering into the discussion of the relative rank of the Protozoa as contrasted with the remaining animal phyla we may accept the usual characterization of Protozoa as one-celled animals which during some part of their life cycle exhibit motility. The phylum is usually divided into four classes, the Rhizopoda, the Mastigophora, the Infusoria, and the Sporozoa. 160820 Following Brumpt we shall include in a fifth class, the Spirochaeta, an important group of organisms regarded by some as bacteria and by others as Mastigophora. ‘The distinguishing characteristics of the classes are given on page 18, RHIZOPODA As far back as 1849 Gros discovered in the tartar on the internal surface of the teeth of man an amoeba which is now known as Endamoeba gingivalis. Since that time a considerable number of species of amoeba have been reported for man and Aas various animals among them at least one species of prime signifi- cance as a cause of dysentery. The earlier workers supposed that the forms parasitic in animals were free living amoebae which - had been taken in with water and had survived as parasites. It is now recognized that these species do not exist free in nature but onky in the encysted stage. From the view point of human parasitology the most important species is Endamoeba histolytica. ENDAMOEBA HISTOLYTICA (E. dysenteriae, E. tetragona). - This is one of several species Tying in the alimentary tract of man. It is the cause of amoebiasis or the so-called "tropical dysentery", a disease which is now known to be wide- spread in temperate zones as well as in the tropics. Location in the host. - Endamoeba histolytica normally lives in thé stbmucosal tissue of the large intestine of man. Carried by the circulatory system and the lymphatics it may infect the liver, lungs, brain, and various other organs of the body. In recent years they have been noted in a number of cases of inflammation of the bladder (Petzetakis, 1925); in a peculiar type of rheumatism of the joints and’ in the lymph | glands in Hodgkin's disease (Kofoid and Swezy, 1922). As far as the biology of the parasite is concerned all of these hab- itats except that in the large intestine must be regarded as secondary and abnormal. | Description. - The active stage of trophozoite of Endamoeba histolytica has essentially the structure of a free-living amoeba. Typically it measures from 20 - 30 microns in diameter, possesses one or two blunt pseudopods, and has the ectosarc, or clear outer layer, distinct from the endosarc, or granular layer. Imbedded in the endosare are usually red blood cells, an import- ant aid in distinguishing this parasitic species from the non- parasitic amoebae which often occur in the intestine of man, The nucleus is excentric in position, small and distinct. In Stained preparations it measures 4 - 7 microns in diameter. On the inside of the nuclear membrane is a thin layer of chromatin and in the center is a small dote-like karysome. L608a4 Development. - There are two methods of reproduction of Endamoeba histolytica. - that of simple binary fission and that of encystment and spore formation. The first occurs in the tissues of the infected organs, the latter by the migration of active amoebae or trophozoites to the lumen of the intestine where they become rounded, decrease in size and lose their food inclusions. This is the precystic stage. By the secretion of a delicate but impervious elastic wall sphaeroidal cysts are formed which measure from 5 - 20/in diameter. In a given infection the cysts may have a limited range of size there being apparently various races of the organism. Within the cysts the nucleus divides into two and then into four nuclei characteristic of mature cysts of this species. In stained cysts there are often to be found in the cytoplasm one or more rodlike bodies with rounded ends which, on account of oe properties are called chromatoid or siderophile odies. | These cysts are discharged from the body, often in enormous numbers and are disseminated on fruits and vegetables, in water, and by houseflies. When taken up by the human host the cyst wall is broken down in the stomach and small intestine and the four small amoebae are liberated and make their way into the tissues of the large intestine. Effect of the host. - The long-continued discussions as to whether Bndamoeba histolytica is pathogenic to the human host have been definitely closed by the extensive studies of recent years. It has been established that the parasite feeds on the blood cells and fluids of its host and that it causes extensive thickening and ulceration of the bowel and other infected organs. Active cases of intestinal amoebiasis are typically characterized by severe dysentery with blood, mucus in which great numbers of the active amoebae are to be found. In regions where it is « common it is the most frequent cause of liver abscess. As pre- viously noted, the parasite has been implicated in various other diseases, Such as cystitis, brain abscess, and a type of arthritis deformans. There is, however, abundant evidence that infections may ex- ist for long periods of time without causing any noteworthy clin- t$cal effects. Such carrier cases are sources of other infections as: well as themselves liable to acute attacks. Occurrence in animals. - Many of the references in litera- ture to occurrence Of Endamoeba histolytica in animals are based on misidentifications of amoebae peculiar to the given host. However, E- Dh ee rteace is transmissible to rats and since it is able to complete its development in these rodents there is every reascn to suppose that they may be factors in the dissemination LE0825 of the infection (Kessel, 1923). Cats and dogs are suscepti- ble to infection, but there is no clear evidence that the cystic state is reached in these animals. Kittens are especially susceptible and the rectal injection of human discharges con- taining motile amoébae is one of the methods of diagnosis of the pathogenic species. Only the cystic stage can be transferred by feeding, as the trophozoites are destroyed by the gastric juices. Artificial cultures. - Early reports of successful cultiva-~ tion Of Endamoeba histolytica have been largely discredited, as due to errors in identification and to contaminations. In 1925 Boeck and Drbohlav reported the successful culture of E. histolytica, on Locke-egg-serum and Locke-egg-albumin. Since that time the work has been repeatedly verified and the method has even been urged as a routine method of diagnosis (Craig and St. John, 1927.), Prevalence. - The idea that amoebiasis of man, or infec~ tion by pathogenic amoebae, is limited to tropical regions has given way before abundant evidence that it is much more wide- spread in its distribution. While especially prevalent in India, China, South and Central America and similar regions, it is frequently contracted in our Southern States and Europe and cases contracted in the Northern United States are by no means rare. The extensive war-time and post-war examinations of home service and foreign service troops and of civilians in- dicate that at least 4% of our population harbor this parasite. Of these probably 95% are carriers who do not show marked clinical symptoms. ‘ Epidemiology. - The chief methods by which the infection passes from man to man are through the handiing of food by cyst carriers, the use of human excrement as fertilizer, and through the agency of houseflies. Root, 1921, observed living cysts in the gut of houseflies up to the end of the second day after in-~- gestion. Kessel's work, supported by that of several other workers, shows that rats and mice also play a role in the dissemination of the parasite. Prophylaxis. - Theoretically the avoidance of infection is very Simple but the necessary measures are not always readily carried out. They consist in the protection of food and drink from contamination by fecal material, whether through the agency of soil, human carriers or insects, The elimination of carriers from restaurants and kitchens is as important here as in the case of typhoid. Proper screening and other protection from flies, the cooking of fruits and vegetables and the boiling of drinking water not known to be safe, constitute very essential precautions. Fruits and vegetables which are to be taken un- cooked may be rendered safe by dipping for 10 seconds in water 160826 maintained at a temperature above 80° C., as recommended by ‘Mills, Bartlett & Kessel, 1925. References. - Recent years have witnessed a flood of literature dealing with amoebic infections of man. Fortunately excellent consideration and bibliographies are afforded by the texts of Craig, Hegner and Taliaferro, and of Wenyon. An in- valuable critical review of the field is that of Dobell, 1919. In addition to these and the specific references in the above discussion, may be cited Boeck and Stiles, 19¢5, incidence in. U. S.; Kofoid, 1923, general, and numerous current contributions; © Walker and Sellards, 1913, experimental amoebiasis in man. FNDAMORBA COLI. - This is a large amoeba living in the lumen of the large intestine and of medical interest because it is often mistaken for the pathogenic E. histolytica. Unlike that form it does not feed on the host tissues and hence it rarely, if ever, contains red blood corpuscles but takes up numerous bacteria, food fragments and starch grains. The active forms are about the game size as those of the pathogenic species but are. more sluggish and have a much less prominent ectoplasm. The nucleus is more distinct in the living trophozoite and has its karysome excantric in position. The cysts of Endamoeba coli vary from 10 to 30/4 in diameter and when mature are 6 nucleate, There is usually present a well outlined glycogen vacuole and the chromatoid bodies when present ‘are splinter-like. ENDAMOEBA GINGIVALIS is commonly found in the tartar of the teeth and was the first amoeba of man to be noted. It is exceed~ ingly variable in size, ranging according to figures of different workers, from 6 to even 60/4. Wo cystic stage is known, trans~ fer apparently being by direct contact from mouth to mouth. In the past this species has been of much medical interest, due to the claim that it was the causative agent of pyorrhoea, a view i again brought forward .byathe carefuliwork of Hinshaw, 1927. ENDOLIMAX NANA (Endamoeba nana) is a dwarf form which is nonpathogenic but which has a 4 = nucleate cyst which has usually been mistaken for that of E. histolytica. These cysts are typically oval, measuring 8 - TOM by 7 - 8A , and are — characterized by having the chromatin clumped in a large blob, rather than peripheral. ‘ BNDAMOEBAE (OF “ANIMALS. - As previously noted, E. histolytica is transmissable to dogs, cats and rodents and prob- ably, to other animals but many of the records of its occurrence are due to failure to recognize that there are closely related species peculiar to the animal host. Of these special interest 1608ol attaches to the following, on account of possible confusion with those of human amoebiasis: - Endamoeba ratti and Councilmania decumani from the rat, and Councilmania muris from the mouse =(Kessel, 1924), and to Endamoecba blattae, Leidy, 1879, from the oriental cockroach, which is of zoological interest as the type of the genus. A recent study of this form is that of Kudo ; 1926, Class MASTIGOPHORA The MASTIGOPHORA, or Flagellata, are Protozoa which are _ provided with one or several whip-like flagellae. Reproduction is usually by simple fission. Formation of protective cysts occurs in many cases. The group is a large one and contains — many free-living forms as well as numerous species parasitic in. animals and plants. The first known intestinal parasite of man “was Giardia intestinalis, a flagellate which has only recently been recognized as of considerable pathologic significance. Certain of the Mastigophora resemble plants in that they ‘are provided with chlorophyll. and may have a cellulose capsule. -These have been placed in the sub-class PHYTOMASTIGINA to distinguish them from the ZOOMASTIGINA which have a holozoic¢c nutrition and are animal-like. It is the latter group which concerns US. * The classification of the Zoomastigina is in a chaotic ‘condition. Since Wenyon's text is destined to be for years the standard English reference dealing with parasitic Protozoa, we shall indicate here his subdivisions of the Zoomastigina and then take up in zoological sequence a few illustrations either typical or of special medical significance. ZOOMASTIGINA A. Monozoic Forms There is a single nucleus and a varying number of flagella and blepharoplasts. 1. Order: PROTOMONADIDA. - The flagella are few in number (rarély more than six). : ; 2. Order: HYPERMASTIGIDA. - The flagella are vevy numerous, 3. Order: CYSTOFLAGELLATA. - Haeckel, 1873, - The body is large and globular, and possesses a peculiar tentacle as well as a single flagellum. 160828 B. Diplozoic Forms There are two nuclei, while the flagella, blepharoplasts, and other structures are similarly duplicated, giving rise to a bilateral symmetry. 4, Order: DIPLOMONADIDA. - With the characters of the Diplozoic forms. C. Polyzoic Forms There are more than two nuclei and numerous flagella and blepharoplasts. 5. Order: POLYMONADIDA. - With the characters of the- Polyzoic forms. : The order PROTOMONADIDA is of interest chiefly because it includes the haemoflagellates of man and animals. In addition to these forms and their close allies, there may be mentioned « as important members of the order Histomonas meleagris (Theobald Smith 1905), the causative organism of the highly- fatal blackhead of young turkeys, and Costia necatrix, a pear- shaped, two or four-flagellated form parasitic on the skin of fish. The haemoflagellates and closely related forms belong! to the family TRYPANOSOMIDAE. They are characterized by a more or less spindle~shaped body, a central nucleus, and by the possession Of a compound nucleus-like structure, the © kinetoplast, from which arises the single flagellum. The family is Of great medical and veterinary significance since it con- tains the organisms of sleeping sickness, Chagas! disease, and various types of leishmaniases of man, and those of nagana and surra, dourine, and other serious maladies of domesticated animals. Other species are parasitic in cold blooded vertebrates and in invertebrates, while still others may have both an invertebrate and a plant host. The question of the evolution of the blood-infesting flagellates is one which has attracted much attention. Wenyon, and numerous other investigators, consider that the trypanosomes of vertebrates were originally purely insect flagellates which gradually became adapted to the blood medium when the insects became blood suckers. Moreover, from a practical view point it is of great importance to distinguish between flagellates peculiar to the invertebrate and those which represent a stage in the development of a cyclic trypanosome. For these reasons it is desirable to consider briefly two genera of flagellates, Herpetomonas and Crithidia which are confined to invertebrate, 160829 chiefly insect, hosts and which are transferred from host to host as cysts in the feces. Flagellates of the genus Herpetomonas are found in the intestinal tract of a large number of invertebrates, 4 : typical form occurring in the housefly. The kinetoplast is at the anterior, rounded end and there is no trace of an un- dulating membrane. In the hind gut of the insect the elongate motile form becomes shortened and rounded, and surrounded by a cyst wall. It is by means of these cysts that infection is spread from one host to another. The genus Crithidia likewise has the kinetoplast anterior to the nucleus but closer to this structure, and the flagellum takes a lateral position and is connected with the body of the organism by short undulating membrane. Many of the so-called Crithidia are now known to be merely stages in the life cycle of vertebrate trypanosomes (See Becker, 1925; McCulloch, 1919). In recent years numerous workers have reported successful Snoculations of laboratory animals with supposedly strictly in- -sect flagellates of the genera Herpetomonas and Crithidia. Interest in the question has been greatly Stimulated by the discovery that herpetomonadlike flagellates are to be found in various plants, particularly in the latex of representatives of the Euphorciaceae. They are transferred by sucking insects. For these flagellates having both an insect and a plant host the generic name Phytomonas has been proposed. The question of their relation to vertebrate infections has not been sat- isfactorily demonstrated but offers a fertile field for further study (See Strong, 1924; Noguchi, 1925, 1926; Noguchi and Tilden, 1926). Of the family Trypanosomidae the type genus Trypanosoma is characterized by the fact that the flagellum arising from the kinetodlast is connected with the entire extent of the body of the organism by a delicate undulating membrane of which it forms the margin. The trypanosomes are known chiefly as parasites of the blood of vertebrates but certain species may also be found in the tissues. Most of the forms which have been studied in detail, undergo a part of their life cycle in some inver~ tebrate, but a very important species, Trypanosoma equiperdum, which causes a venereal disease of horses, is transmitted directly. Owing to their virulent effect on man and animals in Africa, they have been of outstanding interest to all of the nations attempting colonization in that country and no other protozoal parasite has been subject to more searching investigation than have the trypanosomes Since the beginning 160830 of the present century. Trypanosoma lewisi is a cosmopolitan species which has been extensively studied and which may serve as a type. TRYPANOSOMA LEWISI. - This species is common in various species of wild rats the world over and is readily transmissi~ ble to laboratory rats. Description. - T. lewisi has a more or less spindie- — shaped body about 25 min length, and with one edge provided with a delicate, undulating membrane. The flagellum arises near one end, from a highly refractile granule known as the blepharoplast and continues as the thickened end of the un- dulating membrane, to project at the anterior end. Closely associated with this is a larger somewhat rod-shaped structure which is sometimes designated the kinetonucleus but more properly the parabasal body. The combined blepharoplast and parabasal body constitute the kinetoplast. Near the center of the body is the principal nuclevs, or troohonucleus, Movements. ~ The movements of T. lewisi are of two types, a euglenoid body contraction and setond, a very active movement by means of the flagellum. When the parasites are abundant they may be detected under low power by the disturbance of the blood corpuscles. Reproduction. - The reproduction in the blood of the rat is by longitudinal fission. The division of the body pro- toplasm is preceded by the division of the kinetoplast and trophonucleus and the formation of a new flagellum, paraltelling, and closely applied to the original one. For a time the two daughter trypanosomes are connected at their posterior end and under some conditions the division of the cytoplasm at this point may be delayed, resulting in the appearance of multiple divisions, or "rosette" forms. In addition to this process which occurs in the blood of the vertebrate host, T. lewisi undergoes a complicated cycle in the invertebrate host which serves as the agent of transfer from rat to rat. The rat louse, Haematopinus spinulosus may serve in this capacity but as shown by the work of Minchin and Thomson, 1915, the most important vector is the rat flea, Geratophyllus fasciatus. Within the first half hour after being sucked up by the flea the blood in its stomach is still infective on inoculation into a rat but after this brief period the contained trypanosomes undergo a striking cycle of changes and are not again infective until the end of the fifth day. They first enter the celis of the "stomach" of the flea, where they divide to form approximately a dozen trypanosomes very similar to those taken up in the blood of the rat. 1603ol These forms either re-enter cells and redivide or without further delay they may migrate to the hind gut and rectum of the insect. They become inactive, the body is shortened and rounded and the position of the nucleus and the kinetoplast become reversed, producing the sc-cslled "crithidia" forms, Sooner or later there are produced short, stumpy trypanosomes, very different from those of the rat, which pass out with the feces of the insect after the fifth day. These constitute the infective stage which thus is transferred by the excrement of the flea rather than inoculated by its bite. Licked up by the rat or swallowed with its insect host, the trypanosomes appear in the blood in 6 - 7 days. The infection may persist in the rodent for three months or even longer. Though many authors have described sexual forms in this and other species of trypanosomes there is no satisfactory | evidence that the cycle in the insect can be so interpreted, as is that of the malarial parasite in the mosquito. “Artificial culture. - This is one of the early forms of parasitic protozoa to be cultivated with marked success, Novy and MeNeal, 1903, having first grown it on nutrient agar and defibrinated rabbit's blood. Their original formula was simplified by Nicolle, 1908, and under the name of N.N.N. medium, is widely used for the cultivation of the trypanosomes and related forms, Prevalence. - While Trypanosome lewisi is a fairly common parasite of wild rats, the statements current in literature regarding percentages of infection have little value. Like any epidemic disease, centers of infection exist within which there may be a high incidence, while at a given time in other localities the parasite may be very difficult to find. Effects on host. = In general, this species is regarded as non-pathogenic to the rodent host though heavy experimental infections sometimes result in death of white rats. Once in- fected, the rat becomes immune to subsequent infections. Young rats are much more susceptible to infections than are old ones, quite apart from the question of acquired immunity. RELATED SPECIES. - Trypanosoma gambiense is the cause of the deadly African sleeping sickness of man + a disease which has spread widely in the tropical regions of that country since the beginning of the present century. The organisms are found in the blood and in the cerebrospinal fluid in the earlier stages of the disease and are conveyed from man to man by the tsetse-fly, Glossina palpalis. Rarely, this transfer is by direct inoculation from contaminated mouthparts but as a rule it is only after the parasite has undergone a twenty day cycle 1608OL of development in the gut of the fly and is then injected with the saliva of the feeding insect. Most of the present day workers recognize a type of sleeping sickness as due to 4 distinct species T.:rhodesiense, transmissible by Glossina morsitnas. In both tases there is evidence that wild animals serve as reservoirs of the disease. Trypanosoma evansi was the first trypanosome noted as pathogenic. lt is the cause of a serious disease of equines, known as surra, which is prevalent in Asia, North Africa and neighboring islands. In order to prevent its importation into this country the U. S. Bureau of Animal Industry has — found it necessary to adopt stringent regulations controlling transfer of horses from the Philippines. A similar infection known as "mal de caderas" occurs in tropical and subtropical South and Central America. Both diseases are conveyed mechanically by biting flies such as Stomoxys (stablefly) and Tabanus (horseflies). Trypanosoma brucei is the organism of a usually fatal disease of cattle and other domesticated animals known as nagana. It is transmitted by the tsetsefly, Glossina morsitans, but until the work of David Bruce, 1895, this fact Was not even suspected and the bite of the fly itself had long been considered extremely virulant. The epoch-making work of Bruce had a great influence on human and animal disease. Trypanosoma crugi occurs in the blood of man in Brazil, Pern, san Salvador and Venezuela, causing the disease known as Chagas! disease or South American trypanosomiasis. It presents a very different type of development in that the parasites do not multiply in the circulating blood but in the muscles, the — heart fibers, and nerve cells. Here they lose their flagellae, become contracted and rounded, assuming the so-called leishmanoid form. in this stage they divide repeatedly, invading more and more of the tissue. Four or five days after inoculation they transform into trypanosomes which make their way through the tissues and into the blood stream. When taken up by certain Reduviid, or assassian bugs, notably Triatoma megista, they undergo a complicated development and 8 - 10 days later are dise charged with the feces of the insect. Infection of man appar- ently occurs through the rubbing of the fecal material into the wound made by the bug, though the parasites can pass through healthy mucous membrane of the mouth or conjunctive. The natural reservoirs of the disease are thought to be armadillos. Trypanosoma equiperdum represents still another departure from the better known types of trypanosome development. It is the cause of dourine, a venereal disease of horse which is conveyed by coitus. 1608oo Some authorities consider that it represents a specialized life cycle in which the insect host has been dropped out. The disease was introduced into Europe from the Orient early in the 19th century and was first recognized in this country ia. Illinois in 1886, being traceable to a stallion imported from France. In spite of strenuous efforts of the federal authori-~ ties to stamp it out by killing infected animals and by quarantine, the disease was known to exist in at least six West Central States in 1912. - See Mohler, 1911; Mohler and Schoening, 1920. It is now regarded as under control. Trypanosomes are also abundantly distributed in cold- blooded animals. Indeed, the first recorded forms were found in the blood of trout and shortly thereafter Gruby, 1845, proposed the generic name Trypanosoma for the forms which he found in the blood of the frog. The best known of these fish and batrachian parasites undergo a part of their cycle in leeches. References. - Laveran and Mesnil, 1912, comprehensive monograph; for subsequent work see general texts and Tropical Diseases Bulletin. : . | LEISHMANIA ~ Closely related to the trypanosomes are cer- tain minute intrscellular parasites of man and animals classed under the genus Leishmania and often referred to in medical literature as the Leishman-Donovan bodies. They produce two types of disease - the one generalized, or systemic, and the other cutaneous. The former is illustrated by a widely dis-— tributed disease known as kala-azar or tropical splenomegaly, and by various native names. The causative organism is Leishmania donovani, the type of the genus. Leishmania donovani occurs in cells of the spleen pulp, bone marrow and lymphatic glands as a very small rounded or slightly pear-shaped organism measuring 1-2” in diameter, less than one-fourth that of a red blood coupuscle of man. They were long supposed to be degeneration products but through the discovery that they possessed a nucleus, a kinetoplast and a small rod-like body in the cytoplasm the relationship to trypanosomes was recognized. The correctness of this interpre-~- tation was established by finding that the organisms could be ar- tificially grown in blood media and that they then developed into flagellate Herpetomonas forms, very similar to those found in the intestine of various insects. It has been suggested that the leishmaniases of man are transferred by the bed-bug or by sand- flies of the genus Phlebotomus but no satisfactory evidence has yet been adduced. That the parasites are transmitted by some arthropod is most probable, The cutaneous type of leishmaniasis known as "tropical sore”, "Delhi boil" and by various other local names, is an ulcerating 160834: infection of the skin widely prevalent in warm countries of a] both the Old and New World. ‘The causative organism is L. eee tropica, a parasite littie distiaguishabie from L. donovani. Tn this ceaee, too, the method of trensfer is vnknown thoven there seems more reason to believe that the vectors are sand- flies of the genus Phlevotomus. References. - Laveran, 1917, comprehensive; Wenyon, 1922, review; Young and Hertig, 1926, Indian Journal of Medical ~ Research, and Tropical Disease Bulletin for experimental studies. TRICHOMONAS HOMINIS. (T. intestinalis). - The genus Trichomonas contains numerous species infecting cold and warm~- Slooded animals. There are usually recognized three species occurring in man. Of these the best-known is the common intestinal form, T. hominis. Description. ~ Trichomonas hominis is a pear-shaped organism 7 - 15 in léngth by 7 - 10” in breadth. A spherical nucleus is near the anterior end and close to this @ « blepharoplast from which arise three long, forward directed, free flagella; and a fourth directed posteriorly and connected with the body by an undulating membrane. &xtending from the anterior end and projecting candad is a hyaline, non-staining rod known as the axostyle. The function of this rod is problematic but it is generally regarded as a supporting structure. At the base of the flagella is a slit-like mouth, or cytostome, through which bacteria and, occasionally, blood corpuscles are ingested. Reproduction. - Longitudinal fission of the trophozoite is the only known form of reproduction. The supposed cysts, often figured, are plant organisms belonging to the genus Blastocystis. Prevalence. <- While this species is often referred. to as the commonest intestinal flagellate of man there are no definite data to warrant this designation. Pathogenicity. - The available evidence indicates that Trichomonas hominis is non=pathogenic. However it should be noted that Kessel, 1926, produced a fatal diarrhoea in kittens experimentally infected with this species. Method of infection. - Since no cystic stage is known, is difficult to explain the method of transfer of this parasite. The experiments of Hegner, 1926 a, and of Kessel, 1926, in- A@icate that infection may be directly from the trophozoites. 1608 De eeoo RELATED SPECIES. - Similar flagellates of the genus Trichomonas occur in the mouth and in the vagina and are Separated by some workers as distinct species, T. elongata and T,. vaginalis. Other species are common in the caeca of other mammals, birds, reptiles aud amphibians. One of the largest and most available for study is Trichomonas augusta (Tetratrichomonas) which occurs in the intestine of frogs, toads and salamanders. References. - Bensen, 1909, human forms; Dobell, 1909, protozoa of frogs; Kessel, 1926, transfer of T. hominis to kittens; Kofoid and Swezy, 1915, reproduction; Wenrich, 1921, rodent species. CHILOMASTIX MESNILI. - This flagellate which likewise in- habits the large intestine and caecum of man, resembles Trichomonas hominis and is frequently mistaken for it, on hurried examination. It has three anteriorly directed flagellum and a large cytostomal cleft, within which is a fourth flagellum. It may be readily distinguished from Trichomonas by the lack of the axostyle and the undulating membrane. The living organisms exhibit an active, jerky movement as contrasted with the slow- er rotatory movement of Trichomonas. They vary considerably in size, Hegner and Taliaferro stating that "average-sized specimens are from 8 to 14 microns long, others are smaller, and some reach a length of 24 microns. The width is from one-half to one- fourth the total length". Reproduction. - The trophozoite reproduces by longitudinal fission. Lemon-shaped cysts measuring from 7 - 10M by 4 - 6 At are also formed and within these mitotic divisions occur. Care must be exercised to avoid confusion of the cysts with intestinal yeasts. Pathogenicity. - There is no evidence that C. mesnili is injvrious to itS human host. It is apparently about a8 common as ig Trichomonas hominis. Related forms are found in the guinea pig and in a number of other vertebrates. References. - Kofoid and Swezy, 1920, morphology; Leiva, 1921, C. intestinalis from guinea pig; Swellengrebel, 1917, cyst formation. GIARDIA LAMBLIA (Lamblia intestinalis, Giardia intestinalis ). This is a fairly common parasite of the small intestine, duodenum and gall bladder of man. Historically, it is of special interest as being the first protozoal parasite noted for man. Description. - In shape Giardia intestinalis resembies half of a longitudinally split pear, the terminal portion being 1608oF Prophylaxis. « The chief measures for protection against this parasite are proper sewage dispos al and the same general precautions as those against amoebic infections. RELATED SPECIES. - A considerable number of spe cies Ciardia have been described, chiefly infesting mammals. “In general they clos aly resemble each other and those of man gut most workers consider that those of man are not transmissible to animals. Of the described species may be mentioned: - Giardia muris (Grassi 1879) which is found in mice, wild pats and white rats G. duodenalis Da avaine, 1875) in rabbits, G. canis Hegner, 1922, G. eee ee ene 1925 and G. agilis Kunstler, 1ese. The ‘Tastementioned is found in tadpoles but disappears at time of fecckor phosis. It differs Pao typical members of the genus in being much more elongate and slender, the ratio of pody. “length to breadth averaging 4.4. References. ~ Dobell, 1920, Loeuwenhoek's discovery; Fantham and Porter, I9I6, pathogenicity "and sunposed successful transfer of G. lambia; Hegner, jgee2 comparative studies: Simon, 1921, detailed study of G. lanbia ("onterica’), 1922, critique of experimental work. Class tw INFUS ORTA The INFUSORIA are Protozoa of definite form, whose locomo- tory apparatus is consti ituted by a more or less considera able number of vibratile cilia on the surface of the body and which typically possess two forms of nuclei, ~ a vegetative macronucleus and a reproductive micronucleus. In the sub-class Suctoria Gilia are present only during the young stages the adults ob being sessile and in the sub-class Opalinata the two or more nuclei present are of a single type. Dependent on the distribution of the cilia on the surface of the body four orders of the sub-class CILTATA are generally recognized. ae 1. - Order HOLOTRICHA, in which the cilia are distributed more or less evenly over the body. 2. - Order HETEROTRICHA have around the mouth a conspicu- ous aboral zone formed by large cilia or vibratile membranes. They are usually of swimming habit. 3. - Order HYPOTRICHA typically of creeping habit, the dorsal cilia absent and those of the ventral surface often modified to form prominent cirri. 4, - Order PERITRICGHA, whose cilia sre reduced to an aboral zone. Since there is only one important infusorian parasite of man - Balantidium coli - the Monier eh of the class from a 1608 idan ia = ptos ocean tees a Prophy ian. “ bia chief measures for pam etan against this parasite are proper sewage Oe ae and the same eeneral se aeautt he as those ag saint amoeb? » infections. RELATED SPECIES. - A considerable aumber of species Giardia have been described, chiefly infesting mammals. In ge eneral they closely resemble each other and those of man put most workers consider that those of man are not tra asmissible to animals. Of the described species may be mentioned: - Giardia muris (Grassi 1879) which is found in mice, wild pats and. white rats, G. duodenalis (Davaine, 1875) in rabbits, G. canis Hegner, 1922, eee @, Gati Deschiens, 1925 and G. agilis Kuns sEler, L882. The Tast-mentioned is found in tadpoles but disappears at time of metamorphosis. It differs from typical members of the genus in being much more ae Pe and slender, the ratio of body. “Length to breadth averaging 4 References. ~ Dobell, 1920, Loeuwenhoek's discovery; Fantham and Porter, I9I6, pathogenicity and supposed successful transfer of G. lambia; legner , 1922, compara tive studies; Simon, 19el, detaile dq study of G. lambia ("onterica’), 1922, aeieas of experimental work. Class INFUSORIA The INFUSORIA are Protozoa of definite form, whose Locomo~ tory apparatus is cons stituted by a more or less considerable number of tet Labia cilia on the surface of the body and which typically posse two forms of nuclei, ~ a vegetative macronucleus and a reproductive micronucle us. In the sub-class Suctoria Gi118. are present only during the young stages the adults “being sessile and in the sub-class Opalinata the two or more nuclei oresent are of a single typo. Dependent on the Aistribution of the Gilia on the surface of the body four orders of the sub-class CILTATA are generally recognized. 1. - Order HOLOTRICHA, in which the cilia are distributed more or less evenly over the bod; 2, « Order HEPEROTRICHA have " around the mouth a conspicu- ous atoral zone formed by large ciiia or vibratile membranes. They are usually of swimming habit. 3. - Order HYPOTRICHA typically of creeping habit, the dorsal cilia absent and those of the ventral surface often modified to form prominent cirri. 4. ~ Order PERITRICHA, whose cilia sre reduced to an aboral zone. Since there is only one important infusorian parasite or man - Balantidium coli - the significance of the class from a 160858 parasitological viewpoint is usually overlooked. In reality, all of the orders contain parasitic species, some of them ex~ hibiting extraordinary modifications in form and piological adaptations. The simplest of the INFUSORIA are the holotrichous Opalinata which are parasitic in the intestine of frogs and Other amphibia. They possess two or more nuclei which are all of one type. They exhibit a sexual reproduction characterized by the complete fusion of uninucleated gametes. Since represen= tatives of this group from our common frogs are always available for study, we shall consider briefly the best known form, Opalina ranarumn. OPALINA RANARUM is an European form found in the rectum of frogs, toads and a salamander. They are so large that they may be seen with the naked eye as whitish specks in the fecal mass. Structure. - The flattened, oval body is covered by fine cilia which are arranged longitudinally in parallel rows, giving a striate appearance to the organism. There is no trace of a cytostome or other opening. The granular endoplasm contains numerous nuclei which are uniformly distributed and which multiply by mitotic division as the organism grows. Reproduction. - During the greater part of the year multiplication occurs by an oblique division into two parts, each of which is multinucleate. In the spring of the year there occur many rapidly succeeding divisions which finally result in the production of small individuals, 40 - 50/% in length, which contain only a few nuclei. These surround themselves with cysts, measuring 30 - 70M which, passing out with the feces are taken up by tadpoles. From the cysts emerge the enclosed multinucleate ciliates which divide repeatedly and give rise to the small uninucleate gametes. These gametes fuse in pairs and again a eyst is formed, which is presumably taken up by a second tadpole before the young Opalina emerges. When this occurs the large multinucleate forms are produced by growth and nuclear division without accompanying division of the cytoplasm. Related forms. - Metcalf, 1923, recognizes some 140 species and a number of sub-species of Opalinata. Of special interest ig Proto-opalina intestinalis which is only binucleate in the mature Stage. The common species of Opalina in our native Rana pipiens is 0. obtrigonoidea. References. - Konsuloff, 1922, reproduction; Metcalf, 1909, anatomy and reproduction, 19235, anatony and reproduction of Prota- opalina, monographic treatment of group. L608 eeeehe BALANTIDIUM COLI. - This important ciliate of man occurs also in the pig and is transmissible to monkeys. ii lta li Description. - Balantidium coli is a_ large oval pear- shaped organism, measuring 300 - 200 in length by 20 - 70% in breadth (Brumpt). At the anterior end is a slit-like cytostome, or mouth, bordered by the coarse aboral cilia. The remainder of the body is covered by rows of uniform cilia. There are two contractile vacuoles and at the posterior end an anal aperature. The macronucleus is a kidney-shaped body near the center, the micronucleus minute and lying in the depression of the larger one, Reproduction. - Asexual reproduction is by transverse divi-~ sion. A form of sexual reproduction occurs in which two individ- | uals become encysted and are believed to fuse. In addition single individuals may become enclosed in a protective cyst | wall 50 - 60 in diameter. In this condition they are dis- | charged and give rise to new infections. | Pathogenicity. - Balantidium coli is an active parasite, which not infrequently vores into the submucose of the large intestine and causes considerable ulceration. It is un- | guestionably a cause of a specific diarrhoea but, like Endamoeba | histolytica, it may be present without causing definite symptoms. Geopraphic distribution. - This parasite is widely dis- tributed. A number of cases have been reported for the United States, Central America and Porto.Rico, as well as for the Old World. _ Methods of infection of man. - Infection is brought about by the ingestion of the cysts. The experimental evidence indi- cates that man may be infected by cysts from pigs as well as by those from other humans. References. ~ Brumpt, 1909, pathogenicity; Nisbet, 1920, occurrence in the U. 8.3; Walker, 1913, experimental and pathology. RELATED SPECIES. - Balantidium minutum Schaudinn, 1899, has been reported asaparasite of man ‘but is regarded by Brumpt as a coprozoic form. Other species have been reported for cattle, sheep and the guinea pig. Frogs and toads commonly harbor B. entozoon and other species in the rectum and numerous species have been described for invertebrates. of these B. blattarum is frequently to be found in the American cockroach. — NYCTOTHERUS. - Infusoria of this genus are oval or kidney- shaped organisms characterized by a straight, linear peristome 160840 along one border, leading to an oblique more or less curved cytostome in the equatorial region. The macronucleus is almost central and near it is the micronucleus. Three species have been reported for man. but their parasitic nature is questioned. Next to species of the genus Opalina the most common of the. ciliates of amphibians are of this genus, N. cordiformis being the best known. Other representatives of The genus are report- ed for insects, myriapods and crustacea. Glass SPOROZOA | The class SPOROZOA is a somewhat heterogenous group of Pro~- tozoa which are exclusively parasitic and which lack definite locomotory organs, mouth, anus and contractile vacuoles. They produce at some stage in their life history resistant spores which are not, however, the infective forms, but which give rise to sporozoites which are the forms infecting new hosts. The class is commonly divided into two sub-classes - the TELOSPORIDIA and the NEOSPORIDIA. In the Telosporidia the ~ sexual reproduction, or sporogony occurs in the adult organism, when the period of growth is completed. In the Neosporidia, on the contrary, sporogony occurs during the period of growth. The forms of chief medical interest are classed in three orders, the COCCIDIIDA, the HAEMOSPORIDIA, and SARCOSPORIDIA. Three other orders - the GREGARINIDA, the MYXOSPORIDIA and the MICROSPORIDIA contain forms of much zoological interest, as well as of considerable economic importance. We shall consider typical forms of these six orders. : order GREGARINIDA The GREGARINIDA are coelom-inhabiting Sparozoa reproducing typically by spore formation alone, after the fertilizing union of similar gametes. They are very common as parasites of .Inver~ tebrates, chiefly insects, but. the majority of species are probably harmless to their hosts. Dissemination is usually passive, infection being by way of the alimentary canal. In spite of their relative unimportance as. parasites, the generalized life cycle of the Gregarinida and their close rela- tionship to important groups of mammalian and human parasites makes them important objects of study. One of the most widely distributed and best known species is Monocystis agilis. MONOCYSTIS AGILIS - This parasite is found in the seminal vesicles of the earthworm, Lumbricus terrestris. In most regions where this species Of earthworm is common the majority of individuals are infected. If a specimen is pinned out with 160841 the dorsal side uppermost and opened by a longitudinal slit anterior to the clitellum, the three pairs of cream-colored seminal vesicles project from the 10th, lith and 12th segments. If a portion of one of these is removed with forceps and tapped in a drop of water on a slide various stages of the parasite may be found among the brush-like groups of spermatozoa and the spherical sperm morula. Description. - The earliest known stage is a minute nucleated stage, known as the trophozoite or vegetative stage, which lives among the cells of a sperm morula, and grows at the expense of the developing sperm cells. The body is somewhat spindle-shaped and differs from that of many Gregarinida in that it is not divided by a transverse partition, The endoplasm is coarsely granular and contains a single nucleus. After a time the trophozoite enters the seminal fluid and in this stage may move about by a slow gliding movement. Reproduction. - Reproduction is by spore formation only. Two similar individuals, now known as gametocytes, come to- gether without any fusion and form about themselves a two layered cyst wall. Their nuclei divide repeatedly and the daughter nuclei migrate to the periphery of their respective cells and with rounded masses of protoplasm are separated from the remaining cell body, or residual protoplasm, as gametes, The gametes now unite in pairs to form zygotes. Their nuclei fuse and a boat-shaped sporoblast is formed which by the secretion of a hard cyst wall becomes a spore. Finally the spore nucleus and protoplasm divide to form eight sporozoites, or in- fective bodies. Dissemination. - By the death and breaking down of the host or more commonly by its being taken by birds the cysts contain- ing hundreds of spores with their sporozoites are widely dis- seminated. Infection of new hosts probably takes place by in- gestion of these cysts and liberation of the sporozoites in the alimentary tract. References. « Cuenot, 1901; Hesse, 1909. RELATED SPECIES. - A number of other species of wnocystis from the seminal vesicles of carthworms have been described, but their separation is difficult except in the trophozoite stage. Our local small earthworms, Helodrilus caliginosus, are very commonly infected by gregarines of the genus Zygocystis. In this genus two or three trophozoites are usually intimately associated as a compound organism though solitary forms are sometimes present. The developmental stages are similar to those of Monocystis. For a brief discussion of Zysocystis cometa see Mickel, 1925. 160842 Favorite sources of laboratory material illustrative of Gre- garinida are grasshoppers, cockroaches and especially "meal- worms", the larvae of the beetle Tenebrio molitor. Valuable aids to the study of the group are the two monographs by Watson, 1916, (Watson) Kamm, 192. Order COCCIDIIDA The Coccidiida are cell-infesting Sporozoa which typically reproduce intracellularly by asexual spore formation (schizogony), as well as by true sporogony, thus giving a life-cycle with an alternation of asextal and sexual generations. The former provides for the multiplication of the parasite within the in- fected host while through sporogony the infection of new hosts is brought about. After fertilization the oosphere forms sporoblasts which may or may not be covered by a sporocyst mem- brane, and which may each become transformed into one or several sporozoites. The chief differences between the Coccidiida and the typical Gregarinida are, then, the intracellular habitat of the parasites and the interpolation of an asexual cycle. A readily available species for the study of the Life cycle of a coccidian is Eimeria stiedac. EIMERIA STIEDAE (Coccidium oviforme). - This liver-infest- ing parasite is the causative organism of a very serious disease ~ coccidiosis ~ of rabbits. Its ravages are especially severe among young tame rabbits. Description. «- The parasite leaves the body of the host, with Feces, in the oocyst stage. The oocysts are ellipsoidal or ovoid somewhat yellowish bodies varying considerbly in size (33 -~ 43 by 18 - 30”), with smooth, thick shells having a micropylar-like depression at one pole, This gives them some- what the appearance of fluke eggs and they have been frequently mistaken for such. The granular protoplasmic content is at first distributed uniformly but soon becomes collected into a spherical mass. Development. ~ In the presence of moisture and summer temperatures the oocyst becomes mature in three or four days. The nucleus and protoplasm divide to form four sporoblasts and around each of these there is formed a cyst wall, transforming them into ovoid sporocysts. By division each of these forms two sporozoites, and a smail mass of residual protoplasm. ‘The cocysts are now in the infective stage. If taken up by a new host the sporozoites escape from the spores, make their way through the micropyle of the oocyst and enter the cells of the bile ducts. Here they become the rounded schizonts, which ultimately divide into 6 - 30 (Wenyon) asexual”élements known 1608 PEE bers 98 cnmecne tenerPE bers A crecme tr 43 as merozoites. At a certain stage in the cycle there are pro- duced the gametocytes. Unlike those of the Gregarinida, these gametocytes differ in appearance and give rise to strikingly dissimilar gametes. The female cell, or macrogametocyte is distinguishable through its coarsely granular protoplasm, rich in reserve material, while the microgametocyte pos- gesses a clear, more or less fibrous appearance and increases considerably in sizco. The macrogametocyte, by a process of extrusion of chromatin analogous to the formation of the polar bodies of the mammalian egg becomes the mature macrogamete. In the meantime the microgametocyte has given rise to a large number of minute microgametes, one of which enters the mature macrogamete and fertilizes it. A firm resistant wall is formed and the completed oocyst is discharged via the bile ducts and intestine. ? Intestinal Eimeria of the rabbit. - Not infrequently there occurs an intestinal form of coccididsis of the rabbit which may also result in fatal epizootics. This intestinal parasite is often considered identical with that occurring in the liver, but the present tendency is to regard it as a distinct species, E. perforans. Reported human infections. ~ There have been reported several Gases of human infections by Eimeria stiedae and it has been stated that these were especially to be met with in men who cared for rabbits. The evidence in support of these reports is very meager and it is possible thet they are based on misidentification. References. - Metzner, 1903; Perard, 1924; Wasielewski, 1904. RELATED SPECIES. - Three species of Eimeria, - E. wenyonli, B, oxysvora and E. snijdersi, have been described as parasites Sf man but have been shown by Thompson and Robertson, 1926, to have been based on the finding in human feces of cysts of two species of coccidia of herring which had been accidentally ingested. They afford a striking illustration of one source of error in the determination of cysts or eggs from the human. intestine. In addition, a number of important BFimerias of domesti-~ cated animals are known. Of these may be mentioned: Eimeria giirnii which causes a serious and often fatal disease o cattie, E. diebliecki, in pigs in this country and the West Indies, as well as in Europe. Eimeria avium a very common parasite of chickens, turkeys, geese and other fowls which in the case of young birds often causes serious epidemics. 16084.4 ISOSPORA SPECIES. - The genus Isospora is characterized by the fact that the mature oocyst contains two spores, each with four sporozcites. The best known forms are commonly present in cats and dogs, and domesticated foxes are not in- frequently infected by what are probably the same species. Tsospora hominis and Isovora belli have been reported for man. The latter Species, which is apparently the more common has been separated by Wenyon on the basis of its smaller size, It has sporocysts measuring 12 to 14 by 7 - 9M , each containing four sporozoites and a large spherical residual body. Connal, 1922, cited by Wenyon, had an unusual opvortunity to note the time of development and the pathogenicity of tnis species in a laboratory worker who had accidentally ingested mature oocysts. "Six days leter diarrhaea with abdominal discomfort set in. This persisted for four weeks, and oocysts were discovered in the stool three weeks after the onset of symptoms and were present more or less continuously for twelve days after which they were not found. The stools had become normal again and recovery was complete", References. - Connal, 1922; Dobell, 1919, 1926; Hall and Wigdor, ISIS; Wenyon, 1923, 1926. Order HAEMOSPORIDIA The order Hacmosporidia includes the blood~dwelling sporozoa, intracorpuscular, or free in the blood plasma, and with or without alternation of hosts. The group is somewhat heterogeneous. From the zoological viewpoint as well as from the viewpoint of human pathology the most important are the malarial parasites, belonging to the genus Plasmodium. It is generally considered that there are three speciés infecting | man « P. vivax, P. malariae and P. falciparum. A very closely related form which has served much in experimental studies is Plasmodium praecox of sparrows and finches. PLASMODIUM VIVAX. - This is the cause of benign tertian malaria of man, the most common type in this country. Development. - The sporozoites are minute slender bodies which are introduced into the circulation of man by the bite of infected mosquitoes. Once in the blood stream they bore their way into the erythrocytes, or red blood corpuscles, and appear as the "signet-ring" stage characterized by a large un- stained space in the center of the body. This feeding form, or trophozoite, develops as a schizont with granules of 4 characteristic black pigment - haemozdin - in its protoplasm. The nucleus divides and by the end of the 43 hour period after infection the host cell ruptures liberat- ing 12 - 25.asexual merozoites. These reenter red cells and 1608na 45 continue the asexual cycle. Under certain imperfectly understood conditions some of the young trophozoites develop as male and female gametocytes. In the case of P. vivax these are round or slightly oval and being larger than the réd cell cause it to become enlarged. These gametocytes are capable of further develonvment only if taken up by mosquitoes of the genus Anopheles. Under such conditions the macrogametocyte undergoes a process of maturation similar to that exhibited by a coccidian. The microganetocyte, however, pecomes rounded and rapidly produces its gametes in the form of flagella-like structures surrounding « mass of residual protoplasm. This process, known as exflagellation rarely occurs in the vertebrate host but typically in the stomach of the — mosquito. Here one of the microgametes gains entrance into the mature macrogamete and there results a motile zygote known as an ookinete. -This bores through the wall of the stomach of the mosquito where it settles down as an oocyst, without a firm cyst wall, but capable of considerable further growth in size. Its nucleus divides into a large number and about these the proto- plasm becomes aggregated to form naked sporoblasts. The sporozoites are formed directly, without a resistant sporocyst, and escape into the body fluids of the insect. Through this they make their way to the salivary glands thence to be inocula - tea and continue the cycle in man when the mosquito feeds. Periods of inoculation. = In man clinical symptoms of malaria manifest themselves in about two weeks after an inocula- tion by the mosquito. Multiplication in the blood of man is rapid and Ross estimates that 150,000,000 parasites must be prea - ent in the blood to cause clinical symptoms. The developmental cycle in the mosquito requires from 10 - 14 days, but this period may be considerably extended by cool weather, Relation of the cycle of the parasite to clinical symptoms. -— ro Plasmodium vivax causes in man the relatively benign tertian Malaria, in Which the acute attacks of fever occur every 48 hours. These attacks are correlated with the liberation of the merozoites and their toxins into the peripheral blood. It should be noted that multiple infections may occur and that if infected mosquitoes bite on successive days the fever may occur daily. Latent malaria. - Infections of tertian malaria may persist without clinical symptoms for three or four years after the ~~ patient has left a malarious district but on exposure to cold or fatigue the disease may again become active. This so-called ‘Latent malaria is in all probability due to a great reduction of number of the ordinary parasites in the blood rather than to any peculiarity of life cycle. 160846 Prenatal infections. - As might be inferred from the— nature oF the Malerial parasite it is possible for infections to pass in the circulation of the mother to a foetus in utero. Several undoubted cases of this nature are on record, al- though there is no evidence that the oceurrence is a common one. Malarial control. - The ultimate goal of malarial control measures is the extermination of those species of Anopheles | mosquitoes which have been found to act as hosts and dissemina~ tors of the parasites. In this country the U. S Public Health Service has done especially noteworthy work along this line. Since immediate mosquito control is not often feasible, measures to avoid anophelines, such as choice of locality, the least possible exposure in the evening, screening, and the use of bed nets are essential in a malarious region. The sterilization of the blood of patients by an extended treatment with quinine has been shown by Bass, 1919, to be an efficient measure. OTHER SPECIES OF PLASMODIUM OF MAN. - Plasmodium malariae is the cause of guartan malaria in which schizogony requires 72 hours or, in other terms, the acute attack of the disease is every fourth day. The developing trophozoites are more angular than those of P. vivax and the adult parasite does not cause enlargement of the rea corpuscle. The merozoites are few in number, averaging 8 or G- Plasmodium falciparum (Laverania malariae) causes a much more Yntense and frequently Fatal tertian or Subtertian fever. Only the early signet ring forms and the gametocytes are found in the peripheral blood, the schizogony typically taking place in the internal organs and giving rise to a variable number (8 «= 24) of merozoites. The gametocytes, which appear only after a week or ten days of acute clinical symptoms, are of a characteristic crescent shape. References. - The general texts on protozoology, notably those of Hegner and Taliaferro, and of Wenyon, give detailed discussions of the life history of the malarial parasite. Craig, 1926, gives special attention to the medical aspects. For current work on malarial control in this country see Public Health Reports issued by the U. 5. Public Health Service. BIRD MALARIA. - Birds are infected by Plasmodium praecox (Pp. relictum), a species very similar to those of human malaria, It differs from the species infecting man in that it is transmissible from bird to bird by the common culcicine mosquitoes rather than by anophelines. Though apparently rare in this country it has been found several times in English sparrows and has been transferred through hundreds of genera- tions in canaries. As bearing on the question of latent malaria in man, it is significant to find that bird malaria may be 1608e a7 transferred to healthy birds by inoculation of a previously tnfected bird whose verigheral biood parasites had supposedly disappeared months before. A related genus of haemosporidia is Haemoproteus (Halteridium) a form much more common in birds in this country than in Plasmodium preecox. The mature parasite is a large horse-shoe shaped organism partially enclosing the nucleus of the red blood cell rather than pushing it aside as does Plasmodium. In some parts of this country a species of Taemoproteus occurs in over fifty per cent. of the crows. It is of special interest because it was through the studies of MacCallum, 1898, on this form that the true significance of ex- flagellation in human malaria was discovered. The best known species is Haemoproteus columbae which is a parasite of the common pigeon in many parts of the world and which undergoes its sexual development in the parasitic fly Lynchia maura. References. ~ Adie, 1915, 1924 development of Haemoproteus; Ben-Harel, 1925, P. praecox; Taliaferro, 1925, infection and resistance in P. praecox; Whitmore, 1918, Hartman, 1028; Huff, 1928. 3 ome PTROPLASMIDAE Piroplasmidae are minute hacmosporidians which inhabit the rei blood corpuscles of various mammals but which do not form the pigment (haemozoin) which is characteristic of the malarial parasites. They undergo an essential part of their cycle in ticks and are tranemitted by them to their mammalian hosts. The Piroplasmidase are widely distributed, especially in tropical and subtropical regions and are the cause of some of the most devastating diseazes of animals. The first of these to be studied in detail was Piroplasma bigeminum. PIROPLASMA BIGEMINUM (Babesia bovis). - This is the cause of a highly fatal disease of cattle, known in this country as "Texas fever", but widely distributed and more generally known as "red- water" from the fact that one of the symptoms of the disease is bloody urine. Descrivtion. - The organisms appear in fresh preparations as minute pale pear-shaped spots, usually two in a corpuscle. They vary in length from 2 - 4 and in greatest width from 1.5 ~ 2a. The common appearance of two associated parasites is ‘due to dividing forms. They live at the expense of the red corpuscles, as many as fifty per cent. of which may be infected at one time. The characteristic bloody urine is due to break- ing down of the corpuscles, the number of which may be reduced to one-third or less. : 160848 Life cycle. + Piroplasma bigeminum is transferred from animal to animal solely by cattlé ticks of the second genera- tion. It is not the tick which has fed on the diseased animal which transfers the infection but it is the progeny of such ticks. In this country the tick concerned is the common cattle tick of the South, Boophilus annulatus (Margaropus annulatus). By analogy, it has been assumed by some that this cycle was a sexual one but there is no satisfactory evidence that such exists, Methods of control. ~ Knowing the method of transfer of Texas fever, 1ts control becomes primarily a problem in economic entomology - the protection of cattle from the tick and the extermination of the tick. Working on this basis the federal Bureau of Animal Industry promptly established a quarantine to prevent the movement of cattle from tick-infect-~ ed areas, and undertook active measures against ticks in these areas. Through this work, considerable regions have been freed from ticks and released from quarantine. References. - Brumpt, 1920, development; Nuttall, 1915, helpful discussion of piroplasmoses; Smith and Kilbourns, 1895, of great historic and ecconomic interest, as first demonstration of arthropod transmission of disease. Order SARCOSPORIDIA Sarcosporidia are Sporozoa parasitic in the muscle of vertebrates, particularly mammals, although they have also been recorded for birds and reptiles, They very rarely occur in man but are common in sheep, pigs, cattle and horses, appearing as whitish elongate. ovoid bodies often clearly visible to the naked eye. The best-known form is Sarcocystis tenella from the sheep. It is transmissible, by feeding, to mice, and Hartmann ' recommends that material for study be obtained in this manner, allowing two to three months for development. ‘SARCOCYSTIS TENELLA. « The ovoid cysts in the muscle of the sheep attain a length of some 20 mm. (4/5 of an inch). The capsule is of two layers - an outer strongly staining layer showing radial striation, and an inner layer which projects into the cyst, dividing it into chambers. The outermost of these chambers are filled with a number of rounded cells, 4 ~- 7/4 in diameter, which are known as pansporoblasts. Towards the center the chambers are large and contain sickle-shaped spores, or "Raineys corpuscles", while in old parasites the more central spaces are empty except for obviously degenerating bodies. 1608 edepy 49 Development. - The knowledge of the life history of the Sarcosporidia i8 very meager. When fed to mice the spore membranes rupture and liberate amoeboid forms which enter the intestinal epithelium. Here they multiply but soon disappear from the intestine and the earliest stages known in the muscle do not appear until nearly two months later. According to Alexeieff, 1913, the cyst wall and the septa forming the chambers are the product of the host cell, but this interpreta- tion has been criticised. Effect on the host. ~ Sarcosporidia may be present in con- siderable numbers without apparent effect on the host. On the other hand, infections are sometimes so intense as to obviously cause mechanical injury if nothing more. Muscular paralysis in pigs and horses has been attributed to Sarcosporidia but without satisfactory cvidence. Various investigators have succceded in extracting from the parasites a toxic substance known as sarcocystin. Method of transfer. - While several species of: Sarcocystis have been shown to be experimentally transmissible by feeding to rodents, it is puzzling to find that the most common forms are in herbivorous animals, A plausible theory is that the parasites occur in some form in insects which are accidentally taken up by grazing animals, but extensive studies have failed to verify this suggestion. HUMAN INFECTIONS. «- There are some half dozen recorded cases of infection of man by Sarcosporidia, but in none of them were definite clinical symptoms clearly traceable to the presence of the parasites. References. + Alexeicff, 1913, morphology and development; Darling, I909, 1919, human infections; Erdmann, 1910, cxperimen- tal feeding; Scott and OtRoke, 1920, consider that there is an infective intestinal stage. Order MYXOSPORIDIA The Myxosporidia are parasites of cold-blooded vertebrates, especially Known as causing scrious cpidemics among fish. They occur in hollow organs such as the kidnoys, uriniferous tubules and bladder or they may be tissue parasites in the skin, fins and muscles, where they produce tumor-like swellings. They are characterized by the fact that the trophozoite, or feeding stage, is amoeboid and that spore formation commences at an early stage and proceeds continually during the growth of the trophozoite. The spores produced within the protoplasm of the trophozoite are enclosed in a bivalve shell and possess two or, rarely, four distinctive structures known as "polar capsules". These bodies - 160850 when stimulated extrude a long filament which serves to anchor the spore while the infective element is entering the tissues of its host. References. - Gurley, 1894; Kudo, 1919; Thelohan, 1895; Ward, I920. Order MICROSPORIDIA The Microsporidia are closely related to the Myxosporidia Since they possess a polar capsule within which is coiled the polar filament. The spores are minute, frequently less than 5/7 in length, and contain an exceedingly long filament. They ave chiefly parasites of insects, although they occasionally infect fish, The most noted form is Nosema bombycis. . NOSEMA BOMBYCIS. - This is the cause of the famous pebrine or silkworm discase which until the work of Balbiani and of Pasteur, threatened to wipe out the silk industry of France. Form. - The parasites occur in the tissues of the host, including the ovaries, as minute amoeboid organisms which multiply rapidly and become transformed into spores. These Spores are oval, 3" long by 1.5 wide and contain the typical ‘polar capsule. Behind this at the posterior part of the spore is the binucleate infective agent. When taken in by the silk- worm this organism escapes, enters the intestinal epithelium and finally fills the tissues of the body. Development. ~ There are two methods of spread of the disease. ‘The spores passing out with the excrement of the in- fected larvae are scattered on leaves and taken up by other caterpillars. Or, if a diseascd caterpillar succeeds in trans- forming into a moth the parasites which have reached the ovaries infect the eggs and from these are hatched weak, discased cater- Pillars which, though they soon dic, have contaminated the food . of. the colony. Control. - As a result of his studics of silkworm disease | Pasteur found that by microscopic examination of the tissues of the adult moths he could determine whether the infection was ‘present or not. Using only eggs from healthy individuals ho was able to produce healthy caterpillars and thus to reestablish the silk industry of France on a profitable basis. Ina strik- ing manner these methods have been applied in recent years by Howard in China, ; ‘References. - Howard, 1925; Pasteur, 7870; Stempell, 1909, development. 1608ea os iuemaet eee SL NOSEMA APIS. - Closely allied to N. bombycis is a parasite very commonly found in the honey bee. By analogy, it has been supposed to cause considerable mortality but evidence regarding this is unsatisfactory. See Fantham and Porter, 1912; Hertig, 4925; White, 1919. RICKETTSIA BODIES Three important diseases of man, - typhus fever, trench fever and Rocky Mountain spotted fever ~ which are carried by — arthropods, are caused by very minute intracellular, bacterium- like organisms known as Rickettsia bodies. Cowdry, 1926, defines these as “gram negative, bacterium-like organisms of small size, usually less than holf a micron in diameter, which ere found intracellularly in arthropods, wnich may be more or less pleomorphic and stain rather lightly with analin dyes, but which resemble in most of their properties the type species, R. prowazeki, the cause of typhus fever. The name was first applied by Rocha Lima, 1916, to the organisms in lice, in honor of Howard Taylor Ricketts who lost his life in the course of his studies of typhus fever. Stimu- lated by the finding of these bodies in the arthropod carriers of the diseases mentioned and in the endothelial cells of the in- fected humans, extensive studies of insects and their allies have been made, and upwards of fifty species of "Rickettsias" have been described, from almost as many different hosts. It is Sienificant that a number of these are found in non-blood-sucking insects, so that the earlier assumptions that they were all pathogens of man or animals must be discarded. However, it is quite possible that some of those found in plant-feeding insects and mites may be the cause of diseases of plants. Whether they are protozoa or bacteria is an unsettled question,- some workers even regard them as merely cell granules. Their chief interest to the animal parasitologist lies in their host relationships and the evidence of their transfer from the invertebrate to the vertebrate host. References. - Cowdry, 1926; Hertig and Wolbach, 1924; Wolbach, 1919; Wolbach, Todd and Paifrey, 1922. Glass SPIROCHARTA The Spirocheaetes are spiral organisms with flexible, slender bodies, diffuse chromatin and active movements. There has been much discussion as to whether they are bacteria or animals - a futile discussion since classifications are man made, Of char- acteristics usually regarded as protozoal, are their failure to grow on ordinary bacterial media, their reactions to arsenicals, 1608yy 52 and, especially their complicated life cycle which in the best known forms, is undergone in an invertebrate. As a type we may consider Treponema recurrentis. TREPONEMA RECURRENTIS (Spirecnaeta obermeiri). - This is the cause of a relapsing fever of man, characterized by repeated attacks lasting from three to five days, followed by a similar interval of normal temperature. The organisms occur in the blood as slender flexible spirals, averaging 15/* in length and not more than 0.34 in width. Reproduction is by transverse fission. Transmission from man to man is by the body louse. Taken up by these insects the spirochaetes alter rapidly in the stomach and appear to disappear completely. On the sixth day they may be again observed but in the body cavity of the louse. They are not transferred by the bite of the insect but by the crushing of the infected louse and the active penetration of the spirochaetes through the skin or their inoculetion by scratching. Related forms. - Relapsing fevers caused by organisms which are not morphologically distinct from T. recurrentis are widely distributed and have been given different names. The typical form is the European relapsing fever, but in North America, North Africa and various other regions the similar parasite is trans- mitted by the louse and is probably the same species. In West Africa a very similar form is conveyed by the excrement of a tick attacking man. References. - Nicolle, Blaizot and Conseil, 1912, 1915; Nicolle and Lébailly, 1920; Nuttall, 19le. TREPONEMA PALLIDUM (Spirochaeta pallida). - The causative organism of syphilis is an exceeainsily slender spirochaete which differs from the above. in that it is transmitted by contact and is a tissue-invading form. It measures, 5 - 15“ in length by not more than .25-% in width. The spiral turns are about twelve in number and quite regular. It is to be found in scrapings of the primary and secondary lesions of syphilis but is difficult to demonstrate in tertiary lesions. All of the tissues are in- vaded, and especially heavily in prenatal infections. It is transmissible experimentally to monkeys, dogs, cats, guinea pigs and rabbits, and may be cultivated under strict anaerobic conditions. References. - Noguchi, 1911, cultivation; Schaudinn, 1907, pioneer research. 160853 LEPTOSPIRA ICTEROHAEMORRHAGIAR, - This is the cause of a peculiar cosmopolitan disease, known as Weil's disease, or infectious jaundice. The organism resembles Treponema but may be distinguished by its larger number of closely wound spirals. Tt occurs not only in the blood but also in the urine and in the tissues. The principal reservoirs in nature are rats which are commonly found infected. The method of transfer is unknown but it is believed that it may be conveyed through food contam- inated by rats. Severe cases of Weil's disease closely resemble yellow fever and the organism is of special interest because it is now generally beliéved by students of the subject that Leptospira icteroides, described by Noguchi, 1919, as the cause of yéllow fever is in reality Leptospira icterohaemorrhagiae rather than the long-sought organism of that disease. For a valuable discussion of this question, and bibliography, see oe: es in Annals of Tropical Medicine and Parasitology, : £245 - 259. References. - Ido, et al, 1916, prophylaxis; Neill, 1918, infectious jaundice in the U. S.; Noguchi, 1917, in American wild rats. 160854 T - REPRESENTATIVE PLATYHELMINTHES Class TREMATODA Important Generel References In addition to the general text previously cited see Benham, 1901; Braun, 1889-1895; Gamble, 1896; Looss, 1894, 1910; Pratt, 1916; Ward, 1917; Ward and Whipple, 1918. The TREMATODA, or flukes; are exclusively parasitic flat- worms, often leaf-like in shape, without a covering of cilia in the adult state. They possess a well developed alimentary canal with but one opening, the mouth, at the cephalic end of the body. Suckers are developed on the ventral surface and in the region of the mouth, their position and structure being of much systematic value. With rare exceptions (blood-flukes) tremato~ des are hermaphroditic. | The class is divided into. two subclasses, the MON OGENEA and the DIGENEA. As indicated by the names, the monogenetic— flukes develop directly, on a single host, while the digenetic forms require two or more host species for their development. Sub-class MONOGENEA The MONOGENEA are almost exclusively ectoparasitic. They have more than two suckers and often possess, in addition, attachment hooks. The eggs are few in number and usually only a single one is developed at a time. Development is direct and without change of host. The monogenetic flukes are chiefly parasites on the skin and gills of fish, or in the bladder of frogs and turtles. On fish they may occur in enormous numbers and since they feed on the epithelial cells and biood they are sometimes the cause of severe injury and even death of their host. We shall note briefly a few representative forms. The best known life history is that of Polystomum integerrimum as worked out by Zeller, 1872 = '76. POLYSTOMUM INTEGERRIMUM lives in the bladder of frogs. A related species is found in this region (Minnesota) in tree frogs of the genus Hyla and a number of svecies are known to occur in our native turtles, but their life histories have not been studied in detail. For a systematic review of North American forms see Stunkard, 1917. i Description.-- The mature fluke is about 5 mm. long by 1-5 mn. wide, flattened, with four eye spots at the anterior end. 1608oe a 55 The alimentary canal is bifurcate, the two branches being con- nected by many cross canals. At the posterior end are six suckers in a circle, with attachment hooks between them. Life history. - The eggs are iaid in the water by protru- gion Of the body of the worm through the urinary aperature of the frog. About 1000 eggs are deposited in 10 days. After about 6 weeks a free-swimming ciliated larva hatches, but perishes if it does not meet a tadpole within 24 - 48 hours. If fortunate, it attaches to the gills of the tadpole, loses its cilia, and remains for 8 - 10 weeks, forming suckers from behind forwards. When the tadpole transforms, the young fluke enters the oesophagus, passes down the intestine and lodges in the bladder of the frog. It is said to require three years to reach maturity. Diplozoon parodoxum. - This appropriately named fluke .is worthy of mention On account of its remarkable structure. The adult animal is x-shaped, being made up of two permanently fused individuals. They live on the gills of minnows and dis-~- charge eggs which give rise to minute ciliated larvae. If these succeed in attaching to a minnow they develop into a simple larval form long known independently under the generic name Diporpa. These Diporpae develop and mature sexual organs only by conjugation in pairs. The union is permanent, the two individuals fusing at the point of contact and developing with- in each complete sets of genitalia. Gyrodactylus. ~ Flukes of the genus Gyrodactylus are minute, less than 1 mm. in length with a slender, flattened body. The anterior end is prolonged as a pair of conical tips through which empty glands secreting an attachment fluid; the posterior enlarged, disc-like, with two large central hooks and 16 simple marginal hooklets. When these flukes occur in large numbers on the skin and gills of fish they may cause serious injury and death. Related forms on the gills of black bass have been noted as causing heavy losses in New York. Sub-class DIGENEA The Digenea are exclusively endoparasites. They have not more than two suckers and are without hooks. Development is by an alternation of a bisexual with parthenogenetic generations (alloiogenesis); the bisexual generation almost exclusively in vertebrates, the parthenogenetic in invertebrates. (Note, how- ever, that Aspidogaster conchicola which is common in fresh water mussels, completes its development in these molluscs. Other exceptions might be cited). 1608 I~ prssapticeensit 56 { The interpretation of the complicated life history of the | digenetic flukes has been a slow process, dating back to the ' very beginning of microscopy. On account of its great practi- cal importance, the most fully studied has been Fasciola hepatica, the liver fluke of the sheep. It will best serve as an itilustration. Fasciola hepatica. - (Distomum hepaticum). - The liver fluke of sheep and other ruminants. ‘The adult is the cause of "liver rot", an infection which has caused loss in all — countries where sheep are grown. Fortunately it is established only in limited areas in the United States, chiefly in Texas, Florida, Washington and Oregon. Structure. - The adult is a flat, unsegmented worm, en- larged in front, measuring 3 - 6 cm. in length. There are two suckers, one at the anterior end and the second about one-fifth of the way caudad. The cuticle is covered with minute, caudally directed spines. The digestive system is branched, ramifying all through the body. The excretory system is also much branched, with a mesal, main duct opening by a minute pore at the caudal end. The reproductive system is. hermaphroditic, with branched ovaries anterior to the paired, much branched testes, and with very prominent laterally placed yolk glands. Life history. - The adult in the liver discharges its eges which pass out by way of the gall ducts and the intestine. The egg is characteristically capped, or operculate. When it reaches water the ciliated embryo, or miracidium, escapes and enters the pulmonary chamber of a snail of the g ».us Limnacus. There it loses its cilia and transforms into a sac-like sporocyst which from special germ cells produces one or more generations of similar sporocysts. These next develop rediae, characterized by a simple unbranched alimentary canal. The rediae enter the liver and other organs of the snail, and pro- duce internally the cercariae, tad-pole-like with a forked alimentary canal. Boring out of the snail these cercariae settle on vegetation, lose their tails and develop resistant cysts within which they remain as metacercariae, until taken up by grazing sheep. The larval fluke then escapes, passes to the liver and matures. Parasitism of man. - In man, Fasciola hepatica occurs only | as an incidental parasite, usually in small numbers. Several fatal cases are on record. According to Leuckart, natives of Lebanon, who commonly eat raw goat liver, suffer from a peculiar affection due to the attachment of adult flukes in the throat. References. - Hall, 1912, distribution in U. S.; Sommer, 1880, anatomy; Thomas, 1885, development. | 1608 |57 Flukes Infecting the Liver Clonorchis sinensis. - The most common of the flukes in- fecting the liver of man belongs to this species. It 1s common also in cats and dogs and is transferable to rabbits and guinea pigs and rats. Description. - The worms are relatively small, measuring from 10 = 20 mm. by 2 - 4 mm. The second sucker is in the anterior third of the body; the intestinal branches long and simple, reaching the posterior end of the body... The ovary 15 situated about two-thirds of the way caudad and is followed — by the two greatly branched testes. The coiled uterus anterior to the ovary is filled with numerous small, ovoid, operculate eggs, dark colored, measuring 26 - 3044x 15 - 17%. Development. - The miracidia develop in snails of the genus Bythinia, the cercariae attaining full development in three weeks. The metacercariae occur in at least 13 species of fish. When ingested by man or other appropriate hosts they mature in e6 days. Distribution and incidence. - Clonorchis sinensis is wide- spread in the Orient and not infrequently imported cases are noted in the United States. It may occur in enormous numbers in a single host and is apparently a long-lived species. Watson, 1917, reports finding it at autopsy in Chinese in Panama who had not been exposed to infection within the preceding 20 years. Reference. - Faust and Khaw, 1927, monograph; Kobayashi, 1915. Opisthorchis felineus. - Flukes of the genus Opisthorchis are closely related to those of Clonorchis but readily distin- guished by the fact that the testés are compact and lobulated rather than ramified. 0. felineus is widespread in Europe and Asia as a parasite of the dog and cat and occasionally of man. The metacercariae occur in the muscles of various fish. Fed experimentally to dogs they mature in about 12 days. A closely related species Opisthorchis pseudofelineus, Ward, 1901, is fairly common in the liver of cats in this country and makes a valuable species for study. INTESTINAL FLUKES About a dozen species of intestinal flukes have been re- ported as occurring in man. Most of these are of rare occurrs ence and apparently of little medical significance. 160858 ' The largest and best known is Fasciolopsis buski. | Fasciolopsis buski. ~- This is a very common parasite of ' man and of the pig in India, China, Formosa and Indo-China. It is the cause of considerable gastro-intestinal trouble in man. Anemia results and, in severe infections, emaciation. Description. - The worm is large and leaf-like, measuring | up to 7 om. in length and about half as broad. The ventral sucker which lies close to the anterior end, is very large, | three to four times the size of the oral sucker. The twe- branched testes lie mesad in the posterior half of the body. The branched ovary and shell gland are about the middle of the body. The large ovate eggs measure 120 - 130.4 x 77 - 80". Life history. - The miracidia hatch within two to three weeks after discharge of the eggs and undergo the typical cycle in snails of the genera Planorbis and Segmentina. The emerging cercariae encyst on the water chestnut and the water | caltrop. Human infections result from the habit of cracking | these nuts with the teeth. They mature in 90 days. References. - Barlow, 1925; Nakagawa, 1922. re HETEROPHYIDAR. - The family Heterophyidae is made up of a number of very small flukes characterized anatomically by the | fact that the genital pore is sucker~like and located at the side of the ventral sucker. They are of medical and veterinary interest because several species infect man, and the dog and cat. Of special interest is the fact that our native fish, as well as those of Europe and Asia, are often bearers of the encysted metacercariae. Locally, rock bass are especially noted as having the minute, rounded black-pigmented cys ss in the flesh and on the scales. Cuirea has published an import- ant paper detailing his experiments with European species. When the cysts were fed to dogs the flukes matured in 7 days. In Formosa a closely related species, Metagonimus yokagawai, encysting on the scales of fish, has been reported ag a parasite of man. : References. ~ Cuirea, 1924, for biological studies. Ransom, 1920, has published a valuable synopsis of the family with descriptions of new species from the fox, dog and cat. Clinostomum in Fish and Frogs. - In this connection may be mentioned another type of Tarval fluke often found in the muscles of fish and in the mesenteries, imbedded under the peritoneum of the body cavity, and in the lymph svaces between 160859 | the skin and muscles of various parts of frogs. Cort, 1915, who has studied these forms in detail, regards them as dis- tinct spécies, C. marginatum in the fish, and ¢. attenuatum in frogs. The small, cream colored cysts, about the size of a grain of wheat, or a little larger, are especially prevalent in perch and in black bass. When abundant they attract the atten- tion of fishermen who speak of the fish as "grubby". They have been repeatedly mistaken for immature stages of the broad tapeworm. Clinostomum marginatum matures in the mouth or the throat of several different fish-eating birds, notably herons and a stork. C. attenuatum has been reported from the American bittern and the American herring gull. References. - Cort, 1913; Osborn, 1911, 1912; Smallwood, L914. LUNG FLUKES Man is subject to infection of the lungs by a fluke which is very similar to, if not identical with, widespread species occurring in the lungs of cats, dogs and pigs. FPollowing Kobayashi, 1919, we shall consider them under one name. PARAGONIMUS WESTERMANII. = The lung fluke of man is com- mon in Japan, China, Formosa and the Philippines. Rarely, imported cases have been noted in this country. Description. - The mature fluke is around 12 mm. in length and about a third as wide. It is almost round in cross-section. The eggs are 85 = 100-'" x 50 - 67." ,. Develonoment. - The intermediate hosts noted are snails of the genus Melania. The cercariae escape and encyst in the flesh of freshwater crabs and crayfish, with which they are taken up by their definitive host. f Effects on man. - This is one of the most dangerous of the flukes attacking man. It causes a chronic cough and bleeding from the lungs which is sometimes diagnosed as tuberculosis. Sputum examination promptly reveals the eggs of the fluke. Twenty-three cases of cerebral parasitism of man by this fluke are on record. (Yokogawa and Suyemori, 1921). References. ~ Ward and Hirsch, 1915; Kobayashi, 1919. PARAGONIMUS KELLICOTTII. - Ward, 1908, has distinguished as a separate species a lung fluke from cats and from hogs in this country. In cats they have been noted as the cause of a peculiar and persistent couch. The species has been reported 1608 : | |id = 60 from cats in Nebraska, Minnesota, Wisconsin and from hogs in Ohio. The writer has collected it from cats in Minnesota and New York. The life history is unknown. BLOOD FLUKES The blood flukes of man, of which there are three im- portant species, belong to the genus Schistosoma. In the older literature the generic name Bilharzia is used. They are characterized by the fact that they are bisexual and that the two branches of the alimentary canal are united into a single tube in the posterior fourth of the body. The male is the larger and encloses the slender female in a ventral fold, the gynaecophoric canal. The cercariae enter the human host actively, through the skin. Infection by these flukes is known as bilharziosis or schistosomiasis. Until recent years it was attributed to a Single species, Schistosoma haematobium. SCHISTOSOMA HAEMATOBIUM. - This is the best known and the most dangerous of the blood flukes of man. It is readily trans- missible, experimentally, to monkeys, rats, mice and guinea pigs. “Description. - The male is cylindric, 10 - 15 mm. in length and not exceeding 1 mm. in breadth. The oral and ventral suckers are close together. The alimentary canal bifurcates just caudad of the ventral sucker but again fuses to form the Single tube which extends through the posterior half of the worm. The females are cylindrical and thread-like, slightly ex- ceeding the males in length. The ovary is elongate-oval, and lies anterior to the intestinal tube. ‘The yolk glands occupy the posterior part of the body, laterad of the intestine. The uterus is a long tube opening to the exterior by the genital pore immediately caudad of the ventral sucker. It is filled with large, characteristic oval eggs, measuring 160-" x 60-" , without a cap, and tipped by a short, sharp spine. The coupled worms make their way to the finer veins, especially of the ‘bladder and the uterus, and the female alone then passes to the minute branches where she deposits her eggs. The spines engage the wall of the vessel and finally the eggs are forced through into the perivenous tissue. They enclose a well developed miracidium. As a rule they are discharged with the urine, though they may also be found in the feces. Development. - The ciliated embryos, or miracidia, are soon killed by the undiluted urine, but in water they quickly escape by the rupture of the shell and seek snails of the genus Bullinus. L60861 b Failing to find a host, they die within 36 hours. In the appropriate snail they produce sporocysts and daughter sporocysts. The latter migrate to the liver and the gonads and there develop fork-tailed cercariae directly, without produc- a tion of rediae. Escaping from the snail, these cercariae ac- — tively enter the human host through the skin, reach the blood vessels of the liver and attain sexual maturity in about 6 weeks. Effects on the human host. - The cntering cercariae pro- duce a marked itching and often a definite skin rash which may persist for two days. The chief symptoms are due to the movements of the eggs in the mucous membrane of the bladder, where they may be present in enormous numbers. The laceration of the blood vessels re- sults in bloody urine and often acute pain on micturition. In severe cases sooner or later inflammation of the bladder occurs. Not uncommonly the ova undergo calcification and become the nuclei for stones in the bladder wall or cavity. Prophylaxis. - Avoidance of, or sterilization of infected water supply is the obvious method of protection against this parasite. Drinking, or bathing in infected water, or even using it for shower baths may result in contracting the disease. It has even been noted that there is danger in handling newly caught fish, which may have the living cercariae on them. References. ~ Leiver, 1915; Manson-Bahr and Fairley, 1920; Manson's Tropical Diseases, 8th ed. SCHISTOSOMA MANSONI. - For years the presence of large lateral»«spined ova associated with the terminal-spined form had been noted and attributed by most observers to abnormali- ties. In course of time it became apparent that these eggs were found only in feces and that they occurred not only in the regions where Schistosoma haematobium was endemic but com- monly in the West indies and parts of South America where the haematobium was unknown. For the newly recognized form the Ssvecies Schistosoma mansoni was established. Schistosoma Mansoni is the cause of intestinal schistosomiasis, giving rise to dysenteric symptoms, bloody mucous, and at times polypoid growths in the bowel. The worms closely resemble Schistosoma haematobium. They are found chiefly in the branthes of the portal véin and in the mesenteric veins. The eggs measure from 120 - 160. x 40 ~- 60M and are distinguished by the sharp lateral spine. 1608 | | |62 The intermediate hosts are snails of the genus Planorbis. The life history and methods of infection are similar to those of Schistosoma haematobium. SCHISTOSOMA JAPONICUM. - This species is the cause of a serious and often fatal disease of man in China and Japan. Endemic centers also occur in the Philippines. Infection is characterized by great enlargement of the liver and spleen and by intestinal disturbances, thickening of the walls, and formation of ulcers and polypoid growths. The worms are similar in general structure to the preced- ing species. The eggs are smaller, measuring only 70 - 75" x 45 = 55-4. They lack a spine but possess a rudimentary lateral papilla. The life history of Schistosoma japonicum is very similar to that of S. haematobium and was, indeed, worked out as early as 1909 by Japanese investigators. The intermediate hosts are the snails Blanfordia nosophora and Oncomelania hupensis. An important Pactor in the possible dissémination of the parasite is the resistance of the first mentioned snail to dessication for as long as three months. : S. japonicum occurs in cats, dogs and cattle, as well as in man. References. - Faust and Meleney, 1924, monographic account, including detailed account of the earlier work on this species; Cort, 1920, on resistance of the intermediate host. Native species of blood flukes. - Blood flukes of the family Schistosomidae are parasitic in the circulatory system of birds as well as in man, cattle and the previously mentioned hosts. In addition there is a considerable number of species found in our native turtles and fish. These differ from the blood flukes of man in being hermaphrodcitic instead of dioeci- ous, and in various structural details. However, as Ward has pointed out regarding those of the turtle, the material is readily available and affords in this country opportunity for laboratory studies of forms adapted to living in the vascular system. The valuable studies of Stunkard, 1925, should be consulted. LARVAL FLUKES With increasing knowledge of the adult flukes affecting man there has been emphasized the importance of study of the cercariae to be found in snails and of the metacercariae or encysted larval forms in fish, batrachians, crustacea and other aquatic organisms. While a considerable amount of attention has been devoted to these stages by European workers, it is. 16085 oly very recently that the problems which they present have interested American investigators. This rich field has been opened up by the comprehensive studies of Cort; 1915; Faust, 1917; Miller, 1926; under the direction of Dr. H. B. Ward, and by the numerous briefer con- tributions by them and their associates. They will prove of great practical value in ultimately forming a basis for the study of the life histories of many of the flukes infecting domestic animals. Class CESTODA Important General References Benham, 1901; Braun, 1894-1900; Gamble, 1896; Leuckart, 1886; Meggitt, 1926; Pratt, 1916; Stiles, 1906; Stiles and Hassall, 1912; Southwell, 1925; Ward, 1923; Ward and Whipple, 1918; (for classification of fresh water forms). The CESTODA, or tapeworms, are flat worms which have typically the form of a ribbon, made up of a large number of Segments, or proglottides. At one extremity is the organ of attachment, the scolex, provided with suckers of varying form . and number, and in some cases, with hooks. The body cavity is ree lacking, as is also the digestive tract. Food is absorbed directly through the integument. Tapeworms were known to the ancients but down until very modern times: the most diverse views were held as to their nature and origin. Indeed, the present day conceptions as to their life history and the relationships of the adult worms to the cystic stages date back only to the introduction of the experimental method by Klichenmeister, 1851. His successful attempts to produce typical tapeworms in dogs which had been fed cysts from the abdominal cavity of a rabbit, and in cats fed on cysts from the mouse liver, opened up an entirely new field and stimulated work which rapidly elucidated the life nistories of the most important species. With rare exceptions, the known life cycles of the cestodes involve at least two hosts, of different species. Of these one or more is essential to the development of the immature stages and one harbors the adult. An exception is afforded by the rat and mouse tapeworm, Hymenolepis nana, which is able to complete its development in one and the same host. The life cycles of a large and important series of tapeworms infesting cattle, sheep and other herbivores are still a puzzle. It seems prob- able that they require an intermediate host, such as an insect or mollusc, which is accidently swallowed by the grazing animal. 1608eo 64 Considerable confusion still exists in the classification of the Cestoda. This is due to the fact that zoologists, — medical men and veterinarians have often been interested in- dependently and have described species without knowledge of other work in the field. In many cases specimens have been described as new because found in another host, while it was formerly the practice to describe as separate species the : immature and the adult stage. A relic of this early zoologi- cal viewpoint is the retention of such names as Cysticerus cellulosae although it is now known that this is only the cystic Stage of the pork tapeworm, Taenia solium. The class CESTODA is divided into two sub-classes, the Monozoa and the Merozoa. MONOZOA The most primitive of the Cestoda are grouped in the sub- class Monozoa. They are unsegmented forms and are of special interest as showing relationships to the Trematoda, or flukes. Most of the described species infect fish. The larvae of some of the better known forms occur in annelid worms of the family Tubificidae. MEROZOA The typical tapeworms belong to the group Merozoa. We shall use as a type Taenia saginata, the most common of the large tapeworms infecting man. , TAENTA SAGINATA. - This is the beef tapeworm of man. The adult lives only in the small intestine of the human host while the immature stage is found primarily in the intermuscular connective tissue of cattle. Form and structure. - The body is ribbon-like, forming a chain of many segments, with a total length of 4 - 12 meters. The head, or scolex, is minute, (upwards of 2 mn.) somewhat quadrangular, with four suckers but without attachment hooks. The head is followed by a short, unsegmented neck, following which is the trunk, or strobila, made up of a séries of proglottides, which may attain 2000 in number. The alimentary canal, circulatory and respiratory apparatus are entirely lacking. The nervous system consists of two longitudinal cords connected in the scolex and extending through- out the body. A superficial network of fibers is connected with these cords. The excretory system is composed of two longitudi- nal canals on each side, the larger ventral one being connected with its counterpart by a transverse canal in each segment. 160865 Opening into these collecting vessels is a superficial network of fine cavillaries. : Near the middle of one side of each proglottis is e@ slightly raised genital papilla, or pore. The tapeworms are hermaphroditic, each segment as it matures bearing a set of reproductive organs. As is often the case in hermaphroditic animals, the male organs come to maturity before those of the female. They consist of a great. number of rounded testes, whose efferent ducts unite to form a vas deferens which, near the genital pore, enters the cirrus or penis, surrounded by 4& cirrus sac. The female organs consist of the paired ovaries Whose oviducts connect on the one hand with the vagina, passing to the genital pore, and on the other hand, with the tubular uterus which occupies the mesal line of the proglottis. Near the juncture of the oviducts with che uterus is the small‘ round- ed Mehlis! gland, often called the shell gland, while the larger transversely elongate yolk or vitelline gland lies near the caudal margin of the proglottis. Ripe proglottides have the sex organs atrophied, except the uterus, which is very greatly enlarged and with its 15 - 30 dichotomous branchings occupies the entire segment. It is filled with embryonated eggs, of which it is estimated there are 50,000 or more in a single proglottis. The terminal proglottides with their mass of eggs, break from the strobila and pass off with the feces. In the case of T. saginata, these are expelled singly and often exhibit GonSiderable motility after they have left the host. Life history. - The expelled proglottides break down and the eggs containing the six-hooked embryo (hexacanth embryo, or onchosphere) are scattered on the soil and vegetation, to be Still further disseminated by dust, rains, on the feet of man and animals and, to some extent, by flies and other insects. When taken up by cattle with food the emoryonic membranes are digested by the gastric juices and the liberated hexacanth embryo bores by means of its hooks through the walls of the alimentary canal, into the circulatory system, to be carried chiefly to . the intermuscular connective tissue. Here a cyst is formed, the embryonic hooklets are discarded and the scolex of the future tapeworm is developed by invagination of the cyst wall. This larval or asexual form is known as the bladderworm or cysticer~ . cus, the infected meat being known vopularly as "measly". The Cysticerci mature in from eight tc twenty weeks and then if ingested in the living condition by man the nead is everted and attaches to the alimentary canal of its new host, where it develops into the mature tapeworm in about three weeks. Geographic Distribution and Prevalence. ~- Taenia saginata is a cosmopolitan species, occurring wherever beef is an impo> « tart food of man. According to Leuctart, the Abyssinians, 160866 who eat the fresh and uncooked flesh of their cattle, are al- most universally infected and even consider that without the parasite they would be unhealthy. Brumpt states that in France 99 per cent of the large tapeworms of man are IT. -saginata. It is certainly the common Taenia of man in the United States although the observations of the writer indicate that in the Great Lakes region the large fish tapeworm, Diphyllobothrium latum is the more common in man. The once. held view that the pork tapeworm, Taenia solium was common in this country was certainly due to ¢onfusion of that species with T. saginata. Stiles states that of 500 tapeworms of man examined by him from 1891 to 1895, 297 were T. saginata and none were T, soOliume As a rule when infestations with either of these species occur, only a single specimen is found, its presence ap- parently having established an immunity against further infec- tion. As for the cysticerci, or immature stage, the Federal meat inspection retains about 0.6 per cent of the carcasses of cattle examined, or 1 in 166, because of this parasite. This indicates that infections of humans by the adult worm are more common than is ordinarily supposed by medical men. Prophylaxis. - The obvious method of avoidance of infection is the thorough cooking of veal or beef used as food. The cysts ly are unable to survive more than three weeks after the slaughter | of their host and Ransom, 1914, has shown that this period may be reduced to six days if the carcass is kept at a temperature not higher: than 15°F. Taenia solium. - The pork tapeworm of man superficially bears much resemblance to 7. saginata. Like the latter, the adult is found in the smalI intestine of the human host, only. The larval form is found prinarily in the intermuscular con- nective tissue of hogs. Occasionally it is found in various parts of the body of man, and it has been reported also for the dog, cat, rat, and various other animals. These forms obviously play no role in the dissemination of the parasite since they are not used for human food and the cysticerci have no chance for further development. Form and structure.: Taenia solium differ from T. saginata in size, since 1t rarely exceeds 4 meters in length and the number’ of segments is 1000 or less. The head is smaller, globular and in addition to the suckers, has an apical rostellun, which bears a double row of attachment hooks or is "armed", in contrast to the hookless or "unarmed" head of T. saginata. ‘The terminal proglottides are frequently discharged as fragments of a chain, rather than singly. 1608ye a 67 Life history. - The embryos from the discharged proglotti- des when taken up by a pig develop in three or four weeks and may, persist in the host for a year or more. When the cysticerci are taken by man they mature in about three months. Autoinfection of man. - Contrary to the usual rule, the em- bryos of Taenia Solium are capable of developing also in man if taken from soiled fingers or with food or drink or if by re- verse peristaltic movement of the alimentary canal they pass to the stomach. Vosgien, 1911 (cited by Brumpt) has analyzed 807 cases of Cysticercosis and found that in 46 per cent. the cysticerci were in the eye, in 41 per cent. in the nervous system and in only 3.47 per cent. in the muscles, This apparent distribution is doubtless due to the fact that such cases affect ing the eye or nervous system would manifest themselves, while cysts in the muscles would be overlooked. Geographic distribution and prevalence. - The pork tapeworm was formerly assumed to bé the large tapeworm of man but now known to be very rare in the United States and, as might be ex- pected, is abundant only in those regions where it is customary to eat imperfectly cooked or raw pork, in the form of sausages or otherwise. In the United States it constitutes less than one per cent. of the large Taenias of man; Brumpt reports one per cent. for Paris; in Southern Germany it is likewise rare, but has been very common in northern and eastern Germany. Braun points out that even in this section of Germany the incidence has greatly decreased in recent years, due to education of the public regarding dangers from trichina, and to meat inspection. Available data indicate that it is not uncommon in Central America. Prophylaxis. - Avoidance of imperfectly cooked pork. RELATED SPECIES. - The name Taenia was originally applied to tapeworms in general and is stiIT loosely so used by some medical texts. It is correctly applied to those species having a scolex with 4 simple cup-shaped suckers, proglottides usually longer than wide, genital pores alternating irregularly and never on both sides of a segment, and with uterus in ripe segments composed of a median tube and lateral branches. The two species above described are the principal taenias found in man but several others have been reported for the human host. ° The following are a few of the common species infecting animals. - Taenia pisiformis (syn., T. serrata) is the common tapeworm of hunting dogs, the cystic stage being found in the mesenteries and body cavity. of rabbits. This species and the following are of special interest because of being the forms first used by Kiichenmeister 1851, in his classical experimental studies on..the 1608et 68 life history of the cestodes, Taenia teniaeformis (T. crassicollis}), is a common tape- worm Of cats, contracted from eating mice and rats which serve as the intermediate host. In these rodents the cysticerci are to be found in the liver, and dre noteworthy because of the long worm-like form of the invaginated head. The adult worm is armed with very large hooks and practically lacks a neck, the segmentation beginning immediately behind the head. Taenia ovis is a tapeworm of the dog whose cysticerci develop in the Sheep. It is of interest because these mature forms occur in about 2 percent of the sheep inspected in this country, and have been mistaken for cysts of T. solium and the infected mutton condemmed, The work of Ransom, T9I3, has shown the true source of sheep "measles" and that the cysts are not infective to man. Genus HYMENOLEPIS The genus HYMENOLEPIS is composed of small, filiform worms with broad segments, genital pores on one side, a retractile ros- tellum with or without hooks, usually three testes in a trans- verse row in each segment, uterus sacelike, filling the ripe segment. Included in this genus are a number of tapeworms of mammals and birds. Two species are parasites of man. HYMENOLEPIS NANA (Taenia murina, H. murina). This is the dwarf tapeworm of man and rodents. On account of its small Size its presence in man is usually overlooked, except as found in microscopic examination of feces. Description. H. nana measures 5 - 50 mm. (2 inches or less) in Tength and 0.5 = 1 mm. in width and is composed of 100 ~ 200 proglottides; scolex minute, with four suckers and a single row of minute hooks. There are three testes to each segment. Mature and ripe proglottides are much broader than long. The eggs are quite characteristic, elliptical, with two membranes, the outer 30 - 60“ in diameter, the inner 16 - 30 and having at each pole a distinct knob, provided with thread- like filaments. life history. ~ The dwarf tapeworm is unique among the cestodes of man in that the entire life cycle may be complete in the single host. The embryonated eggs taken in with food or drink, or from soiled fingers, liberate the hexacanth embryo which bores into the intestinal mucosa. Here it transforms into a minute cysticercoid, resembling the cysticercus of Taenia saginata In general structure but differing from it in being of Small size and lacking the fluid filled cavity. In less than a 160869 week this cysticercoid becomes mature and drops into the lumen of its host, evaginates its head and attaches, and promptly develops into a mature tapeworm in the same host that it entered as an embryo. The entire cycle is completed in 15 - 20 days. is ; Geographic distribution and prevalence. = The dwarf tape- worm 18 a cosmopolitan species, though until the development of the practice of making microscopic examinations of feces in diagnosis work, it was rarely recognized. It is now considered the most common tapeworm of man in the United States. Stiles found it in 5 per cent. of the children of an orphanage in the District of Columbia; Frey found it in 22.per cent. of the children in a Texas orphanage. The worms occur in large num- bers, more than 2000 having been recovered from a single host, ‘There is abundant evidence that it is injurious to its host, Prophylaxis. - Since it.is clearly established that in- fection of man by Hymenolepis nana may be acquired from rats and mice, and that development is direct, without intermediate host, it is obvious that protection of food from contamination by these animals is essential, The danger of direct infection from the human host must also be borne in mind. It is not un- common to find the parasite infecting several or all members of a family. References. = Joyeux, 1916, 1920; Ransom, 1904; Stiles, 1903; Woodland, 1924. | se HYMENOLEPIS DIMINUTA. ~ This species, which is likewise common in rats and mice, has been noted as an incidental parasite of man. Unlike H. nana, it requires an intermediate host in its life cycle. coe : Description. - H. diminuta is much longer than is H. nana, since it varies in léngth from 20 = 60 cm. {8 - 24 inchés), and in width from 3 - 4 mm. The rostellum is small, piriform, and — is unarmed. Mature segments are 0.75 mm. long by 2.5 mm. broad, Life history. ~- The larval stage is capable of developing in a wide series Of insect hosts, chiefly cereal-infesting species. The cysticercoids have been noted in the larva and adult of the moth Pyralis farinalis, an earwig, Anisolabis annulipes, the ten- ebrionid beetles, Akis spinosa, Scaurus striatus, and Tenebrio molitor, the rat fleas Ceratephyllus fasciatus and Xenopsylla : @heopis. There is even évidence that certain myriapods may serve as intermediate hosts. The most frequent are the rat fleas and ‘the adults of the beetle Tenebrio molitor. When the infected in- sects are fed to rodents the complete development of the tapeworm . takes place in a little less than three weeks. | 4.608ye 70 Geographic distribution. - Something over 70 cases of in- fection of man by this parasite are known and these are very widely distributed geographically. Of the 17 cases occurring in the United States, 3 are known to the writer to have been found in Minnesota. Considering the fact that the infective Stage occurs in an insect, it is natural that most of the re- ported cases were in young children. It has been found in from 15 to 20 per cent. of the rats examined by the writer in Minneso- ta and Brumpt found it in 55 per cent. of those examined in Paris. References. - Joyeaux, 1920; Ransom, 1904; Riley and Shannon, 1922. RELATED SPECIES. +» Hymenolepis carioca is a very delicate, thread-like species which sometimes Occurs in great numbers in the intestine of chickens. Related species in water fowls are known to undergo their early development in Cyclops and other minute crustaceans. A systematic review of the avian species of Hymenolepis and related genera is given by Mayhew, 1925. Genus DIPYLIDIUM Scolex with four round suckers and retractile rostellum which is armed with three or more rows of minute hooks with broad insertions. The reproductive organs are in duplicate, with a pore on each side of the proglottis. The uterus of the ripe segment breaks up into capsules which contain a number of epegs.. DIPYLIDIUM CANINUM, (Taenia cucumerina, T. elliptica). - This is the commonest tapeworn of pet dogs and cats. Numerous cases of its occurrence as an incidental parasite of humans, par- ticularly young children, are on record. Form and structure. - The mature worm is rather small and: Slender, measuring from 10 ~- 40 cm. (1 - 4 in.) in léngth; the retractile rostellum is provided with three or four rows of , minute, easily detached hocks; the sucksrs are relatively large and ellipsoid. The mature proglottides somewhat resemble cucumber seeds in shape and like others of the genus, are pro-. vided with a genital pore on each side and with double sets of reproductive organs. The mature segments may measure up to 1 cm, in breadth. Life history. - The eggs are discharged in brick-red packets of 8 to I5, formed by diverticula of the uterus. As in Hymenolepis, the larva is a minute cysticercoid. Melnikov, as Tong ago a8 1869, showed that the intermediate host was the dog louse and later it was found that the parasite also developed in the dog or cat flea the embryos being taken up by the larva 1608ee 71 of the insect. The animal becomes infected by biting or licking up its insect pests and the worm matures in about two weeks, Human infections are due to the accidental ingestion of the insect host, through feeding with, or fondling, cats and dogs. Human infection. - Of the 76 cases summarized by Blanchard, 1914, S50 per cent. were of children less than six months old. Vacca, 1909, noted infection in an infant of about twenty days. On attempting to locate the source of this remarkably early in- fection it was learned that a cat which had been brought into the house six days after the birth of the child harbored 3l specimens of Dipylidium caninum and on examination of fleas from its fur cysticercoids were found. References. - Blanchard, 1907, 1914; Diamare, 1893; Grassi and Ravelli, I888; Melnikov = Razvedenkov, 1869; Riley, 1910. RELATED SPECIES. ~ Dipylidium sexcoronatum, also occurring in both dogs and cats, closély resembles D. caninum but may be dis- tinguished by the fact that it has six rows of hooks on the rostellum, instead of three or four. At least four other species have been reported for the cat. Genus DIPHYLLOBOTHRIUM Tapeworms of the genus DIPHYLLOBOTHRIUM differ from those already discussed in two important characteristics. The attach- ment organs, on the scolex, are elongated, slit-like suckers and the genital pore is in the mid-ventral line. The uterus : forms a rosette, discharging its eggs through a pore, rather than breaking down and scattering the eggs en masse. The forms in- festing man have undergone unfortunate shifts in nomenclature, being commonly classed as Bothriocephalus or as Dibothriocephalus. DIPHYLLOBOTHRIUM LATUM. (Bothriocephalus latus. Dibothriocephalus latus). = The broad tapeworm, or, fish tapeworm or man is found as adult im the small intestine of man, dog, cat and fox. The immature stage occurs as a worm-like plerocercoid in the viscera and muscles of a considerable variety of Tish. Structure. - The mature worm is the largest of the tape- worms reported for man, since it may attain a length of 15 meters, or éven more, and vossesses from 3000 to 4000 proglottides, The Ovoid head has two long sucking grooves, or bothridia, The proglottides are much broader than long and in their center is the uterus in a rosette-like coil. The genital pore is situated on the mid-ventral line and slightly further back is a second opening through which the eggs are laid. The latter are large, elliptical, brown, and are provided with a cap or operculum. They average in size 70“ by 45.4 , 1608oe Development. - As in the case of the flukes, the dis- chargéd éggs, after a considerable period in water, release a ciliated embryo, which in this instance is known as a coracidium. It swims about actively for a time and on being taken up by certain minute crustaceans of the genus Cyclops and related: forms, it loses its cilia and undergoes the first stage of larval development. If the crustaceans are eaten by a perch, pike or various other fish which serve as hosts, the ‘larval’ tapeworm works through the walls of the alimentary canal and in the viscera or muscles it becomes the elongated worm- like plerocercoid. Development is completed when this plerocer- ‘coid is taken in viable condition into the alimentary tract of man ‘or of one of the carnivores which serve as primary hosts of the tapeworm. Braun's experiments indicated that this re- quires some five or six weeks, but, according to Parona, eggs are discharged in 24 days after infection. The mature worm is noted for its longevity, one case recorded by the writer having served as host for over thirteen years. Action on the host. = In addition to the usual gastro-intes-~ tinal disturbances, patients who harbor the broad tapeworm fre- quently suffer from.a severe anemia, resembling pernicious anemia. 50 commonly is this associated with infection by this species | that physicians recognize a “bothriocephalus anemia". It not infrequently results in death if the worm is not expelled, but promptly clears up if the parasite is removed. That this condi- tion is caused by a toxine. secreted by the worm has been claimed by various workers and seems demonstrated by the work of Schaumann and Talquist, 1898. These investigators fed dogs on fragments of the worm and in other.instances injected extracts of the strobila. The result was marked anemia, the red blood corpuscles being reduced from a normal of 7,200,000 to 3,400,000 per cubic millimeter.. | Geographic distribution. - The broad tapeworm is widely dis- tributed in Europe and in parts of Asia. It is also found in Africa and in.the United States. In Europe it is especially prevalent in the Baltic region and in Scandinavian countries. | Until recently it was supposed that all cases noted in the United. States wore imported, but it is now known that the’ infection is. endemic in at. l@ast.tie Great.Lakes region, and Manitoba. 7 _ Prophylaxis. - According to Braun, it is necessary to cook fish for at least ten minutes in order to insure the death of the plerocercoids. An important factor in control measures is the prevention of discharge of segments and eggs from patients into water, and the resultant infection of crustaceans and fish. It is significant that the first case of human infection by this tapeworm which was known to have been contracted in the United States: was in a town settled largely by families from endemic 16087O - centers in Europe and that the sewage of the village was dis~ Ze charged into a small lake in its limits. Magath found all the pike and pickerel examined from this lake infested with the plerocercoids of this tapeworm. References. - Braun, 1881, 1883; Essex, 1927; Janicke and’ _ Rosen, 1917, (development); Magath; 1927, 1928; Riley, 1924, ww. 1928, (endemic centers in the U, S.); Schaumann and Talquist, 1898; Sommer and Landois, 1872, (anatomy); Vergeer, 1928. RELATED SPECIES. - A few isolated cases of infections of man-by other species of DIPHYLLOBOTHRIUM have been noted. Tape- worms of this group occur in dogs and in various fish-eating mammals and it is not improbable that they may be found as rare . incidental parasites of man. In this connection it should be noted that under the group name SPARAGANUM there have been reported several instances of the infection of subcutaneous and other tissues of man bw ~“* larval forms related to Diphyllobothrium. These casee-are apy parently very rare. RELATED GENUS - Worms of the genus DIPLOGONOPORUS resemble those of Diphyllobothrium in having suckers as slit-like | furrows, and very short and broad proglottides, but the repro- ductive organs are in duplicate in each proglottis, and there ‘ are two genital pores, submecian in position. The worms are chiefly parasites of whales and seals but several noteworthy cases of human infestation are known. It is probable that the intermediate hosts are fish. Genus ECHINOCOCCUS Tapeworms of the genus Echinococcus are characterized by the very small size of the strobila and by the fact that it is composed of the head and three proglottides, of which only the terminal is gravid. The larval stage is a thick-walled cyst with many brood capsules containing scolices. The generic name ‘Taenia is usually applied to these worms but the characters @iven are sufficient to necessitate classing in a separate genus. One species is of very great significance in human and veterinary medicine. ECHINOCOCCUS GRANULOSUS. (Taenia echinococcus; Echinoc.. coccifer echinococcus). - This is the hydatid tapeworm which is known chiefly by its very large, multiple-headed cysts, re- ported for some 40 mammalian hosts, including man. The adult is found in the dog, jackal and wolf, which are often heavily .infected. Rarely, it has been noted in cats and can be trans- ferred to them experimentally, though with difficulty. 160874 Apparently the most common of the intermediate hosts is the hog. form and structure. - The echinococcus tapeworm is the smallest of the several tapcworms affecting the dog, since it measures only 3-6 mm (1/4 in) in length. It is composed of three segments and the scolex. The head is very small, with a prominent rostellum armea with a doubles row of hooks. The terminal ripe proglottid comprises about one ralf of the entire length of the worm. It contains from 400 to 800 eggs, a rée- latively small number. . Development. - When the eggs discharged with the feces of tis’ dog: are taken up by one of the 40 or more mammals which may serve as intermediate host, the embryos escape and pass to varie. ous organs. A favorite location for cyst development is the . liver, 46.4 per cent. of the recorded cases for man affecting this-organ. Wext in preference are the lungs, with 8.76 per. ‘cent. of cases, but almost any tissue is liable to infection. ‘Having settled ina given tissue, development is very slow. By the end of the fifth month the cyst is-about a centi-~ meter in diameter, but it is still several months or even years. before head development occurs. It often attains the size of an ‘orange, and even that of an adult human head. Instead of one - invaginated scolex 2 single cyst may develop thousands, each capable of developing into a tapeworm when taken up by a dog. These larval heads develop within brood capsules budded from. th: inner wall of.-the cyst, and each contains from 1 to 120 heads. Since: the entire cyst has developed from a single egg we have here a. typé. of polyembryony. When ingested by the primary host they complete their development in from.4 to 10 weeks. It is. not surprising. that they” may occur in very large numbers, 3000 or more, in a.dog, since a single feeding on infected. organs _-_ would result in taking in great numbers of scolices, each capable. of. developing into an adult in the primary host. . Effects. - The hydatid tapeworm is the most dangerous of ‘those infecting man, although occurring only in the larval stage. About-14 per cent. of the known cases resulted fatally. Frequent- ly-the cysts do not produce any symptoms until secondary infec- — tion,occurs, and.then there is the picture of an acute infection. Adominal hydatids sometimes rupture spontaneously. and cause death from the absorption of very toxic substances found in the finid which fills the cyst. In other cases the rupture of the cyst results in urticaria, due to sensitization of the host against. hydatid antigen. Geographic distribution and incidence. - The hydatid tape- worm-:is very widely distributed. Notable centers of infection have long. been Iceland, parts of. Australia, the Argentine Republic and Uruguay. Some 350 cases of human infection have ; | “608yi 75 been reported for the United States, most of them imported cases. It is significant that in recent years the cysts have. been found in alarming numbers in cattle and hogs in Virginia, Oklahoma, Arkansas, and Louisiana, thus indicating that dogs in these regions carry the adult worms and are a menace to man. Prophylaxis. - A consideration of the life history of the hydatid tapeworm shows that the only feasible method of preven- tion of the disease in man and animals is through control of the primary host in regions where the parasite is endemic. Organs infected with the cysts should be burned to prevent their transfer to dogs; rigid precautions against contamination of food and drink should be enforced, stray dogs should be killed, and others treated and controlled. References. - Blanchard, 1905, prophylaxis; Leuckart, 1886, for detailed life history studies; Magath, 1921, for methods of diagnosis; Johannides and Riley, 1924, for recent summary; Teichmann, 1898, analysis of 2,452 case records. Genus MULTICEPS Under the genus Multiceps are classed several species of tapeworms which resemblé Echinococcus in that the immature stage develops many heads, or, in other words, is polyembryonic. This cyst is known as a coenurus and differs from a hydatid cyst in having a thin wall and in lacking brood capsules. The adult worms are relatively large and are not to be distinguished from those of the genus Taenia.: Like Echinococcus their primary hosts are the dog and related carnivores. MULTICEPS MULTICEPS. (Taenia coenurus; Coenurus cerebralis). - One of the most important tapeworms of domesticated animals is this species which is the cause of “gid" in sheep. It is widely prevalent in Europe and there are apparently several endemic centers in this country, the most serious being in Montana. The eggs discharged from an infected dog or wolf are taken up by sheep in grazing and the hexacanth embryo passes to. the brain where it develops as a multiple~headed coenurus, which may attain the size of a hen's egs. Death commonly results 7 to 9 months after infection. Wolves and dogs feeding on the dead. animal continue the cycle. One well authenticated case of hu- man infection by this cyst is reported by Brumpt. References. - Brumpt, 1927, human case; Hall, 1910, general. Seta oer Ransom, 1905, presence in American sheep, and control. RELATED SPECIES. - Multiceps serialis, another dog tapeworm, is a common parasite-of- rabbits in this country, occurring. as large,. many headed cysts:in the muscles. It seems most commonly... found in jack-rabbits. This and related species are discussed by 1608ee 76 Hall, 1910 and 1919. The latter paper treats of the adult taenoid cestodes of the dog, cat and related carnivores of domesticated animals and even of man. Bearing on this topic is also a valuable review by Hall, 1915. 3 Phylum NEMATHELMINTHES References In addition to the general texts see Baylis and Daubney, 1926; Hall, 1912; Hetherington, 1923; Neveu ~ Lemaire, 1912; Ransom, 1911; Stiles and Hassall, 1920, 1926; Ward, 1923; Yorke and Maplestone, 1926. : The NEMATHELMINTHES, or threadworms, are characterized by their cylindrical, spindle-shaped, or thread-like, unsegmented body covered by a thick cuticle. The so-called body cavity is usually spacious. The sexes are, with few exceptions, separate. | The phylum is a large one and contains both parasitic and free~- Living forms. The classification of the group has long been in an un- satisfactory condition which Yorke and Maplestone's comprehen~ sive treatment of those infecting vertebrates will do much to clarify. Since their treatise will be the standard guide for years to come, we shall use their major groupings, even though they differ somewhat from those at present most used in literature. Yorke and Maplestone recognize two classes, the NEMATODA and the ACANTHOCEPHALA, or thorny-headed worms. ‘The members of the Nematoda possess an alimentary canal but lack a proboscis, those of the Acanthocephala lack an alimentary canal but possess a proboscis which is usually protrusible and almost invariably: furnished with hooks. , The class NEMATODA contains two orders, the Eunematoda and the Gordiacea. : 3 The EUNEMATODA are "nematodes in which the body cavity is not lined by epithelium, the gonads being continuous with their ducts. Occasionally the posterior portion of the alimentary canal may atrophy in the sexually mature worms. Lateral chords present; cloaca absent in the female." . The GORDIACEA are the sdé-called "hair-snakes"and are often placed in a separate class, the Nematomorpha. The most obvious characteristic is the absence of an alimentary canal in the adult stage. "The body cavity is lined by epithelium; the gonads are not continuous with their ducts, the ova being discharged 1608AE onssage cerns 77 into the body cavity and then passing into the ducts". “Lateral chords absent; cloaca present in the female". The species of chief economic importance in the higher animals belong to the order EUNEMATODA, defined by Ward, 1916. In addition, this order contains many species parasitizing in- vertebrates, some very important enemies of plants, and a vast number of free-living forms. Many of the species infesting animals pass a part of their life cycle free in the water or in damp earth. The majority of the nematode parasites of the higher animals are oviparous, though some are viviparous, notably Trichinella spiralis and Filaria bancrofti. The eggs may be pro-- vided with a firm resistant shell, serving to protect the embryo or unhatched larvae from unfavorable conditions. Such, for instance, is the case with the eggs of various ascarid parasites and of the whipworms of man and animals, which may live for months or even years in viable condition in the soil. Others, © such as hookworm eggs, are thin-shelled and hatch soon after their discharge. The newly hatched larvae typically undergo two molts before they become infective. In some cases the second larval skin remains as a sheath to be cast off as the infective third stage enters its definitive host. After entrance into the host there are two additional molts before sexual maturity is attained. Development may be either direct (Ascaris, and whipworm) or through an intermediate host (Trichinella, Filaria). Entrance to the host may be either active or passive, but the studies of recent years have shown that even in the latter case there are often complicated migrations in the host body before maturity is attained. _ Eight superfamilies of the Eunematoda are recognized by Yorke and Maplestone, who give the following key for their separation: 1. Heterogenetic, parasitic form par- msenomenetic . « «6 « -» Rhabdiasoidea. Not heterogenetic, parasitic forms sexually differentiated. . 2 1608hs iid 7 ; 78 Oesophagus consisting of a narrow tube running through the centre of a row of single cells for most OF 208 260nth . 9s Oesophagus not consisting of a narrow tube running through the centre of a row of single cells Males with a bursa copulatrix. , Males without a bursa copulatrix . Bursa copulatrix cuticular and supported by rays . . . Bursa copulatrix muscular and not supported by rays . . . Oesophagus dilated posteriorly into a bulb usually containing a denticular apparatus and fre- quently separated from the rest of the oesophagus by a con- BEPSGCLON 6 6 ok 8 Oesophagus not dilated posteriorly 5-9 OB OULU. 6 A OS Head with three large lobes or lips: relatively stout worms. . Head without three large lobes or lips but with two lateral lips, or 4 or 5 small lips, or lips absent; relatively slender, filiform worms; Usually with two lateral lips, chitinous buccal cavity or vestibule usually present, vulva usually in the middle of the body or posterior to it; parasites of alimentary canal, respiratory system, or orbital, nasal, or oral GCOVAGLGS «2 0 4 Usually without lips, buccal cavity or vestibule absent or rudi- mentary, vulva almost invari- ably in the oesophageal region; parasites of circulatory or lym- Phatic systems, or muscular, or connective, tissue, or of serous CAViGiCS 1. 2 «© +2 1608 Trichuroidea. Strongyloidea. Dioctophymoidea. Oxyuroidea. Asecaroidea,. Spiruroidea, Filarioidea.79 ! ‘Without attempting to enter into details of classifica- tion, we shall quote the summarized characteristics of these superfamilies and consider under each a very limited number of important species. Superfamily ASCAROCIDEA "Bunematoda; usually fairly large and stout; head bilobed; oesophagus frequently more or less enlarged posteriorly, but without a definite spherical posterior bulb containing 4 valvular apparatus (except in Dujardinia, where there is a small, unarmed bulb), with or without diverticula. Spicules equal or unequal. Females not much larger than the males. ASCARTS LUMBRICOIDES. - This is a cosmopolitan and one of the most common of the intestinal parasites of man. The same, or at least a very closely related species is a very common parasite of pigs. Description. - The mature males measure 15 - 17 cm., the females 20 - 25 om., and are pointed at both ends. They are of a pale yellow or whitish color, somewhat resembling a large earthworm. The head is provided with three lips - a dorsal and two latero-ventral, - bearing papillae. The caudal end of the male is-curved towards the ventral side and bears two spicules. In the female the caudal end is conical and straight. The vulva is situated about the anterior third of the body. The eggs, of which a single female may produce more than 26,000,000 are ellipsoidal, 60 - 75” x 40 ~ 50” and are covered by a transparent, mammillated albuminous sheath which gives them a very charscteristic appearance. They are dis- charged in an unsegmented condition. Development. - The eggs in the presence of moisture and warmth undergo repeated segmentation and in 30 ~ 40 days develop infective larvae. In regions with sustained high tem-~ perature and moisture this period may be considerably reduced. They are capable of resisting dessication and other unfavorable conditions for long periods. Davaine kept them for 5 years in water and it is probable that they live even longer in moist earth. When taken in food or drink by the human host, the ‘larvae are released in the stomach. It was formerly supposed that they immediately made their way to the intestine and there developed directly into the mature worm. The researches of Stewart, Ransom, and others have shown that the liberated larvae pass to'the liver and then to the lungs, appearing in the latter organs about a week after ingestion. By the tenth day they are migrating up the trachea, whence they enter the oesophagus and then pass down into the intestine. Here they complete their development and are discharging eggs in about a month's time after being taken into the body. In the course of their 160880 migration through the body cf the host, larvae may be carried to developing young in the uterus and thus prenatal infec- tions arise, although the experiments of Martin, 1926, would indicate that this does not occur as readily as has been supposed. Effects on the host. - Ascaris lumbricoides may be present in ereat numbers in the human host. in extreme cases upwards of 1000 have been reported and instances of 100 or more are not uncommon. strongyloid larvae which resem le “ ae 2 1. uU u> § oes ¢ U t 4 Ct fH M } eT OC. or en ss ¢ jae He Cr: 3 ° mM F See ctw O cw Oa tS t ja) - ct » oD ta ce - Strongy toices Sa China, | 1 wide srperate Limates the free-living v>? a SUP ft ppl ess an < sf z ; - 3 es ° 4 a es on ee ne ih 4 a a sh ‘ a4 Eropay eas" - This 18 essen a GaLNSst pe aot cc meemmanetoatinnn : 4 en by : 7 . . Cee a aa OOF Saan a 3 a a Referencése = Sanagrounc 1926, includes extensive LVN i Sis < 3 71 > | “~* a | bibliography -« qo J PTs LOT capiwy?r ee wate Va HO ~ i | ‘ 5 « 45 ¢ RELATED SPROUL. = Cisse ly relatec species occur in bie GOK, ae eg ae an c 2 c 2 i 9 . x mal rabbit and sheep and various other mammeis. (_ Rhebdconema nigrovenosum, angiosvomum ae TAC I ; — AVA CY $ tha . met aa We gee a nicrovenosum) S Nei y ,OMmmon 172 the lunges nr Ere -3,600aTC. 12C0r Ce se >. ea 3 Amn aATtAe Nhe mone Levey “ar fees LWe Sana oipiens, and otnerse the e ges + Une we i j > coc j menregregeny er oy P > and ar aw ft trachea of the frog and are then sw of 1608ty o7 development to the hatched larvae are to be found in the in- testines When they reach the exterior, if the temperature is high, they soon transform into adult males and females. The fertilized female produces rhabditiform larvae which enter the larynx of frogs and thence pass to the lungs. GORDIACEA The GORDIACEA are long slender, hair-like worms popularly known as “hair-snakes". ‘The body is cylindrical, with a blunt or rounded head end and is ornamented with various areoles, scales and papillae. The alimentary canal is present in larval forms but is atrophied in the adult worms. The early stages are parasitic, chiefly in the larvae of aquatic; insects, though they have been reported for spiders, oligochaete .worms trematodes (Cort, 1919) and even for fish and frogs. | The older larvae are very commonly found in grass- hoppers, crickets. and some other terrestrial insects. They play an important role in the natural control of some of these {here are various records of the occurrence of species of Gordiacea as incidental parasites of man but as Brumpt points out, these are very questionable and can be established only by carefully conducted experiments. ‘References. - May, 1919; Montgomery, 1904; Ward and Whipple, 1918.7 Class ACANTHOCEPHALA The Acanthocephala are characterized typically by the presence Of a protractile proboscis, armed with numerous ‘hooks. The alimentary canal is lacking. The larval stagés are found in certain crustacean, insects, fish-and small mammals. The- adults, are. especially abundant in birds and: fish. In.recent. years Van Cleave has undertaken a comprehensive study of our North American forms and has added greatly to the knowledge ‘of the group, | Two and possibly three species are recorded as rire m parasites of man.. ECHINORYNCHUS GIGAS (Gigantorhynchus gigas)-.-Thig.is“a.. common parasite of hogs which attains about the same .Sike as, Ascaris lumbricoides but which is immediately distinguishable «| its Spiny proboscis, buried deep in the intestinal wall, and poy its slight, superficial annulations. The eggs are 90 ~- 100". ~ long, nearly cylindrical with a three-layered: sholl. .of which the L608“age 98 middle is the thickest. The discharged eggs, containing well developed embryos, are taken up by the larvae or "opubs" of May-beetles, which serve as intermediate hosts. Records of human infections by the adults are very rare, put apparently well established. MONILIFORMIS MONILIFORMIS (Echinorhynchus montiformis) is a normal parasite of rodents but is capable of developing in man. Its intermediate host is a cockroach, Blaps mortisaga. References. - Chandler, 1921, Moniliformis in U, eet. Grassi and Calandruccio, 1888, life history of Moniliformis ; Kaiser, 1893, general treatise; Luhe, 1911, systematic; Van Cleave, 1919, et al., North American forms. HIRUDINEA _ The HIRUDINEA, or leeches, belong to the phylum Annulata, having the body composed of similar segments, a body cavity, and an alimentary canal furnished with two openings. From other members of the phylum the leeches are distinguished by having the body marked externally by secondary rings and by having at each end a sucker. ‘The mouth, at the base of the anterior sucker, possesses, typically, three cutting plates. Leeches are temporary parasites or, may directly attack smaller forms as predators. As parasites they attach to the skin, or to mucous linings of the nose, mouth and similarly accessible cavities. While most of the species are aquatic, © the land leeches of India, the Philippines, Australia and South America are famous for their attacks on man and animals. ‘Their action on man depends on their numbers and localiza-. tion. The mouth parts are so developed as to cause free bleeding which may continue after the leech is gorged and leaves its host. Since their attacks are practically painless a considerable loss of blood may result before they attract attention. When they are accidentally taken in with drinking water and attach in the pharynx, or nose, or similar locations they may do serious damage. Horses are particularly liable to this form of attack, the ‘parasites attaching to the lips, cheeks, pharynx or other parts of the mouth. In severe cases it is necessary to remove them with forceps or by the hand wrapped in a towel. Some species have a poisonous saliva, causing inflammation, urticaria and more or less serious nervous trouble. Others are .-’ ‘known to be carriers of trypanosomes of cold-blooded animals and 4t is believed that “mal-de-caderas", a South American trypanosomiasis of horses is similarly carried. 160899 Formerly, leeches were much used medically to produce bleeding, and they were not oly collected for sale but were cultivated in great numbers. Professor Nachtrieb states that one American leech farm sold as many as 1000 or more & day. "Today leeches are so seldom used that few young people have seen a medical leech, and most physicians of today do not know how to apply a leech properly". --. References. ~ Moore, 1918; Nachtrieb, Hemingway and Moore, I9IZ, BIBLIOGRAPHY (See, also, the list of comprehensive texts, PP. 13S: 3) The bibliography of animal parasitology is so extensive that the most which can be done here is to call attention .to a few papers which are comprehensive, or which are of local interest. Text references not included may be located through the Quarterly Cumulative Index to Current Medical Literature. AcKkert, J. E. and Payne, Florence K., 1920. Investigations on the control of hookworm disease. xii. Studies on the : occurrence, distribution and morphology of Necator suillus, including descriptions of other species of Necator. Amer. Jour. Hyg. 3 (1): 1 - 25. Adie, H., 1915, The sporogony of Haemoproteus columbae. Indian Tour. Med. Res. 2: 671 - 680, 5 pls. _..- «+. 1924, The sporogony of Haemoproteus columbac. Bull. Soc. Path. Exot. 17: 605 ~ Glo. Alexander, M. E., 1923. Trichiniasis, endemic and sporadic, with a review of the present status of the treatment of the disease. Amer. Jour. Med. Sci. 165: 567 ~- 577. -Alexeieff, A., 1913. Recherches sur les Sarcosporidies. Arch. Zool, exper. 51: 521 - 569. pls. 7 - 9. Andrews, J. Me, 19266 Coccidiosis in mammals. Amer. Jour. Hyg ° 6: 784-798 6 Ashford, B. Ke and Gutierrez Igaravidez, P., 1911. Uncinariasis (hookworm disease) in Porto Rico:= a medical and economic problem. Washington, Gov't. Printing Office. 455 pp. Augustine, D. L. 1925. Investigations on the control of hook- worm Qisease. xxiii. Experiments on the factors determin- ing the length of life of infective hookworm larvae. Amer. jour. Hyg. 3 (4): 420-443. Numerous other papers bearing on this topic, in same journal 102e - 1608LOO Augustine, D. L., and Smillie, W. G. 1926. The relation of the type of Soils of Alabama to the distribution of hnook~ worm disease. Amer. Jour. Hyg. 6 (1): 36-62. Barlow, C. H., 1925. The life cycle of the human intestinal fluke Fasciolopsis buski (Lankester). Amer. Jour. Hyg. Monographic ser. 4 Tit + 98 pp., 10 pls., 12 text figs. Bass, C. C., 1919. Studies on malaria control. 1X Effective and practical treatment of malaria to disinfect persons and to prevent relapse. Jour. Amer. Med, Assoc. 75: 21-23. Baylis, H. A. and Daubney, R., 1926. A synopsis of the families and genera of Nematoda. xxxvi + 277 pp. British Mus., Londone Becker, E. R., 1923a Observations on the morphology and life cycle of Crithidia gerridis.. Patten, in the water strider, Gerris remigis Say. JOure Parasitol. 9: 141-152. 1923b. Observations on the morphology and life history of Herpetomonas muscae-domesticae in North American muscoid flies. Jour. Parasitol, 9: 199-213, 1926. Endamoeba citelli sp. nov. from the striped ground squirrel Citellus tridecemliniatus, and the life-history of its parasite, Sphaerita endamoebae sp. nov. Biol. Bull. 50: 444-453. Benham, W. B., 1901. Platyhelmia, mesozoa and nemertini. In E. Ray Lankester, Treatise on Zoology, pt. 4. 212 pp. London. Ben-Harel, S., 1923. Studies of bird malaria in relation to the mechanism of relapse. Amer. Jour. Hyg. 3: 652-685. Bensen, W., 1909. Untersuchungen uber Trichomonas intestinalis und vaginas des Menschen. Arch. f. Protistenkunde, 18: Lid ws D Se Fad. Bettison, W. L., 1926. Trichinosis. Report of four cases, with recovery, occurring in the University of Michigan Health Service. Jour. Amer. Med. Assoc, 86: 609-615. Blanchard, R., 1905. Prophylaxis de la maladie hydatique. Arch. ce parasitol. 9: 451. 1907. Parasitisme du Dipylidium caninum dans 1Tespéce humaine a propos dfun cas nouveau. Arch. de parasitol. ll: 459-471. lgl4. Encore un cas de Dipylidium caninum a Paris. Arch. de parasitol. ° . - ° ees Boeck, W. Ge, 1921. On the longevity of human intestinal protozoan cysts. Amer. Jour. Hyg. 1(5<6): 527-540. 1608ag 101 Boeck, W. C. and Drbohlav, J., 1925. The cultivation of Hndamoeba histolytica. Amer. Jour. Hyg. 5(4): 371-407. Boeck, W. C. and rete C. W., 1925. Studies on various in- testinal parasit s (especially amoébae ) of man. Bull. No. 155, Hyg. Lab. Weak. xxvi + 2028 pp. 80 figs. Braun, M., 1881. Zur Frage des Zwischenwirthes von Bothriocepha-~ lus latus Brems.. Zool. Anz. 4: 595-597. -~-- - -~ 1883. Bothriocephalus latus und scine Herkunft. Arch. f. path. Anat. 92: 564566. ---- = 1889-1893. Section Trematoda, in Bronn's Klassen und Ordnungen des Thier-Reichs,. 4: 2OQ#9505,. ~ - ~ ~ ~ 1894-1900, Section Cestoda, in Bronn's Klassen. und Ordnungen des Thier-Reichs. 4: 957-1751. Brown, H. W., 1927. Human Ascaris as a household infection. Jour. Parasitol., Urbana, Ill, 13(3): 206-212 . i : +4 4 * = ¥ Brumpt, He, 1909. Demonstration du r6le pathogene du Balantidium coli. Enkystement et conjugaison de cet infusoire. Oe Ke Soc. Bi Gis Par +4, 67: 1036 -~--~ -- - 1914. Le xenodiagnostic. Application du diagnostic de guelques infections parasitaires et en particulier a la trypanosome de Chagas. Bul. soce pathol. exot., Paris. 7: 7066710. ~~ ~~ -- ~ 1920. Les piroplasmes des bovides et leurs notes vecteurs Bull. Soc. path. exot. 13: 416-460. w= = = - = - 1927. Précis de parasitologie. 4ed. 1216 nD. 736 figs. 2 plas Masson et Cic. Paris. Butschlii, 0., 1880-1889. Protozoa. Bronn's ae sen und ordnungen des Thier-HReichs. I. “055 pp. to ibsie Caldwell, F. C. and Caldwell, ©. L., 1926. Are Ascaris lumbricoides and Ascaris suilla identical? Jour. Parasitol., Urbana, IIT. 13(2): 141-145, Calkins, G. Ne, 1909. Protozoology. 547 pp. New York. Lea and Fiebd iger ® -“- + = = ~ = = = 1926. The biology of the Protozoa. ix.+ 623 pp. Phil. and New York. Lea and Fiebiger, L608L02 Caullery, M., 1922. Parasitism and symbiosis in their relation to the problem of evolution. Transl. from Revue scienti-~ fique 1919. Smithsonian Inst. Ann. Rept. for 1920, PP. 399-409 » Chandler, A. Ce, 1921, Notes on the occurrence of Moniliformis spe in rats in Texas. Jour. Parasitol., 7: 179-183. sw a 6 « « « 1923. Speciation and host relationships of parasites. Parasitology. 15: 326-339. Ciurea, J., 1921. Surla source dlinfestation par 1'Eustrongyle geant (Eustrongylus gigas Rud.) C. R. Soc. biol. Paris. 85: 532-534 e ~=- =~ = =~ = 1924. Heterophyidés de la faune parasitaire de- Roumanie. Parasitology, Cambridge, 16(1): 1-21, 5 pls. Connal, A., 1922. Observations on the pathogenicity of Isospora hominis Rivolta, emend. Dobell, based on a second case o Suman coccidiosis in Nigeria; with remarks on the signifi- cance of Gharcot-Leyden crystals in the faeces. Trans. Roy. Soc. Trop. Med. and Hyg. 16: 220245 Cort, W. W., 1915. Notes on the trematode genus Clinostomum. Trans. Amer. Micr. Soc. 32: 167-182. 6 = =» « 1915.. Some North American larval trematodes. Illinois Biol. Monographs. 1(4): 447-532, 8 pls. we ww 1956, Gordius iarves parasitic in a trematode. Jour. Parasitol. 1: 1988199. ~~ = 1980, On the resistance to desiccation of the sntermediate host of Schistosoma japanicum Katsurada e ae JOUP « Parasitol, 6: 84-85. . . . « « - 1922, Numerous papers dealing with hookworm problem, in Amer. Jour. Hygiene. Cowdry, Ee V., 1926. Rickettsiae and disease. Arch. of Path. and Laboratory Med. 2: 59-90. onree Craig, C. F., 1926. A manual of the parasitic Protozoa of man. viii + 569 pp. Philadalphia. ‘Lippincott. Graig, C. F. and St. John, J- He, 1927. The value of cultural methods in surveys for parasitic amoebae of man. Amer. Jour. Trop. Med. 7(1)- 39~-48. 7 1608« 103 Cram, Eloise B. 19e4. The influence of low temperaturés and of "disinfectants on the PBS | A: Ascaris lumbricoides JOUr « Agric. Research, Wash. 5): 167-175. oe Ss = » = 1905, Ascariasia in preventive medicine. Amer. Jour. Trop. Med. &(1): 91-114. --- - - - = 1925. The egg-producing capacity of Ascaris lumbricoides. Jour. Agric. Research, Wash SOCIO): Cuenot, L., 1901. Rearches sur ltevolution et la conjugaison des grégarines. Arch. Biol. 17(4): 581-652, pls 18-21. Darling, S. T., 1909. Sarcosporidiosis, with report of a case in man. Arch. Internal. Med. 3: 183-192, ~ = = - = = - 1919. Sarcosporidiosis in an East Indian. Jour. Parasitol, 6: 98-101. ae we 1988, Comparative helminthology as an aid in the solution of ethnological problems. Amer. Jour. Trop. Med. 5(5): 523-358. Diamare, V., 1893. Il genere Dipylidium Lt. Atti r. Accad. d. sc. fis. e mat. Napoli (ser 2) 6: Sl pp. 3 ou Dobell, C., 1909. Reésearchés on the intestinal protozoa of frogs” and toads. Quar. Jour. Micr. Sci. 53: 201-266, pls. OnO 6 anes 4.2 1918. Are Entamoeba histolytica and Entomoeba ranarum the same species? Parasitology, Cambridge. 10: 294-310, 2 = -- = ~ = 1919, The amoebae living in man. A zoological monograph. vi + 155 pp. 4 double pls. New York. Wood & Co. ~- --s-- - 1919. A revision of the coccidia parasitic in man. Parasitology. Jl: 147-197. Ss = e = = = & 1920... The discovery of the intestinal protozoa of man. Proc. Roy. Soc. Med. is: 1-15. os «ae = «'» 1926, -0n the species of Isosvora parasitic in man. Parasitology. i8(1): 74-85. Doflein, F., 1916. Lehrbuch der Protozoenhunde, 4ed. xv + 1190. ' Gustav. Fischer. Jena. 1.608104 Erdmann, R., 1910. Beitrage zur Morphologie und Entwicklungsgeschichte des Hammelsarcosporids in der. Maus. Centralbl. f. Bakt. 1 Abt. Orig. 53: 510-516, 4 pls. Fantham, H. B. and Porter, A., 1912. A bee-disease due toa protozoal parasite (Nosema apis). Proc. Zool. Soc. London, W1l: 625-626. we ee e - = = we = = + 1916. The pathogenicity of Giardia intestinalis to mén and experimental animals. Brit. Med. JOUP. me LOOm-141. Faust, E. C., 1917. Life history studies on Montana trematodes. Illinois Biol. Monographs. 4(1): 1-120, 9 pls. Faust, E. CG. and Khaw, Oo-Keh., 1927. Studies on Clonorchis Sinensis (Cobbold). Amer. Jour, Hyg., Monographnic ser. SB, xi +284 pp., 14 pls. and 33 text figs. Faust, E. C. and Meleney, H. E., 1924. Studies on schistosomia~ sis japonica. Amer. Jour. Hyg., Monographic Series No. Oe 559 pp., 56 pls. and 25 text figs. Fibiger; J., 1913. Untersuchungen uber eine Nematode (Spiroptera SP. n,) und deren Pahigkeit papillomatése und carcinomatose Geschwulstbildungen in Magen der Ratte hervorzurufen. Zeitschr. f. Krebsforsch., Berlin, 13: 217-280, 14 pls. Francis, E., 1919. Filariasis in Southern United States. Bul. 117. Hygienic Lab., Public Health Serv., Washington. 56 pp. Filleborn, F., 1908. Ueber Versuche and Hundfilarien und deren Uebertragung durch Micken. Archiv. fur Schiffs-und Tropenhygiene 12: Beiheft 8, 45 pp. 4 pls. “ee em - 1913. Die Filarien des Menschen. In Kolle and Wassermann's Handbuch der path. Mikroorganismen, @ ed., 8: 185-544, pls. 1-6, F Gamble, F. W., 1896. Platyhelminthes and Mesozoa. Cambridge Natural History vol. @, Pp. 1-96. London, Grassi, G. B. und Calandruccio, S., 1888. Ueber einen Echinorynchus welcher auch in Menschen parasitirt und dessen Zwischenwirth ein Blaps ist. Centralbl. f. Bakt. etc. 33 521-525. Grassi, G. B. e Rovelli, G. 1888. Intorno allo sviluppo déi cestodi. Nota preliminare. Atti r. Accad. d. Lincei, Roma, Rendic. An. 285 (ser.4) 4: 700-702, 1608LOS Graybill, H. W. and Smith, Theobald, 1920. Production of fatal blackhead in turkeys by feeding embryonated eggs of Heterakis papillosa. Jour. Exper. Med. 3105): 647-655. Gurley, R. R., 1894. The Myxosporidia or psorosperms of fishes and the epidemics produced by them. Rept. U. 5. Fish Comm. for 1892. pp. 654504, pls. 1-47. Hadwen, S., 1917. Anaphylaxis in cattle and sheep produced by the larvae of Hypoderma bovis and Oestrus ovis. Jour. Amer. Veter. Med. Assoc. Sl: 16-44. Hall, M. G., 1910. The gid oarasite and allied species of the cestode genus Multiceps. l. Historical review. Bull. 125 Bur. Animal Indust., U. S. Dept. Agric. 68 pp. me ee - 1911. A comparative study of methods of examining feces for evidences of parasitism. U. S. Dept. Agric., Bur. Animal Indust. Bull. 135: 1-36 ~ «= » « = ~ - 1912. Our present knowledge of the distribution and importance of some parasitic diseases of sheep and cattle in the United States. U. S. Dept. Agric., Bur. Animal Indust. Circ. 193: reprint from 27th Ann. Rept. of the Bureau, pp. 419-4635. _ = - «+--+ 1915. The dog as a carrier of parasites and. disease. U. S» Dept. Agric., Bull. 260, 27 pp. _ - « «== «1919, The adult taenoid cestodes of dogs and cats, and of rélated carnivores in North America. Proc. U. 5. aw ew ew we ew = 1923, Pinvorm infection in man and its treatment. Therapeutic Gaz. Hall, M. C. and Wigdor, M., 1918. Canine coccidiosis, with a note regarding other protozoan parasites from the dog. _gour,. Amer. Veter. Med, Assoc. 6: 64-76, Harris, W. H. and Browne, D. ©., 1925. Oxyuris vermicularis as. a causative factor in appendicitis. Jour. Amer. Med. Assoc. 84: 650-654. . Jartmann, M., 1921. Praktikum der Bakterioclogie und ’. ... Protozoologie. Zweiter Teil - Protozoologie..4 ed. viil + 146 pp. Jena. Gustav Fischer. Hartmann, M. and Schilling, C., 1917. Die pathogenen Protozoen und die durch sie verursachten Krankheiten. Zugleich eine Finfihrung in die allegemeine Protozoenkunde. x + 462 pp. 337 figs. Berlin, Springer. 1608en renee . %, LOG . Hegner, R. W., 1924. Parasitism among the protozoa. Scienti- fie Monthly. 19: 140-155. -~--- -~ - - 1926a. Animal infections with the trophozoites of intestinal protozoa and their bearing on the functions of cysts. Amer. Jour. Hyg. 6(4): 595-601. -- -- -~ - 1926b. The biology of host-parasite relationships among protozoa living in man. Quarterly Rev. of Biol. 1(5): 593-418. -~ == = - =~ = 1927. Host-parasite relations between man and his intestinal protozoa, xiii + 231 pp. New York. Century Co. Hegner, R. W. and Payne, G. C., 1920. Surveys of the intestinal protozoa of man, in health and disease. Scientific Monthly. 1921: 47-52. Hegner, R. W. and Taliaferro, W. He, 1925. Human protozoology. xix + 597 pp. New York: Macmillan. Heller, A., 1905. Darstellung des Entwicklung von Oxyuris vermicularis. Verh. deutsch. Gesell. Naturf., u. Aerzte. "4(2)3 Eee Herrick, W. W., 1915. Review of recent studies in trichiniasis. Jour. Amer. Med. Assoc. 65: 1870-1872. Hertig, M., 1923. The normal and pathological histology of the ventriculus of the honey-bee, with special reference to infection with Nosema apis. Jour. Parasitol. 9(3): 109-140, pls. 9-IT, cS Hertig, M. ‘and Wolbach, 5. B., 1924. Studies on Rickettsia-like microorganisms in insects. Jour. Med. Research. 44(3): 329-274, pls. 27-50. aa Hertwig, 1891b. Beitray zur Frage der Entwickluns der Rinderfinne. Zeitscher. f. Fleisch - u. Milchhye. Berlin. 7 oe . ‘ « é : 4 Hesse, E., 1909. Contribution a l'etude des Monocystidees des Oligochetes. Arch, de Zool. Expér. (5) 3: 27-301. | Hetherington, D. C., 19235. Comparative studies on certain features of nematodes and their significance. Illinois Biol. Monographs. 8(2): 62 pp., 4 pls. Heubner, 0., 1922. Studien uber Oxyuriasis.. Jahrb. f. Kinderheilkunde 48: l-el. L608LOT Howard, C. W., 1925. The sericulture industry of China. Canton Christian College, Coll, Agric. Bull. 52 PDs Tdo, Yutaka, Hoki, Rukoro, Ito, Hiroshi and Wani, H., 1916. The prophylaxis of Weil's disease (spirochaetosis icterohaemorrhagica) Jour. Exper. Med. 24: 471-485. Janicki, C. and Rosen, F.; 1917. Le cycle évolutif du Dibothriocephalus latus. Bull. de la soc. neuchateloise des sci. naturelles. 42: 19-55. - ee ee we we = = & = 1917. Der Entwicklungszyklus von Dibothriocephalus latus L. Experimentelle Untersuchungen und Beobachtungen. Oor.-Bl. f. Schweiz. Aerzte, Basel. 47; 1505-1520. Joannides, M. and Riley, W. A., 1924. Echinococcus cyst in the scapular area. Arch. of surgery. 9: 557-544. Joyeux, Ch., 1916. Sur le cycle evolutif de quélques Cestodes. Bull. soc. path. exot., Paris. 9: 978-585. -- ee ee 1920. , Cycle evolutif de quélques cestodes. Recherches experimentales. Bull. biol. de France et de Belgique, suppl. 2: 219 pp. 7 pls. Kaiser, J. E., 1893. Die Acanthocephalen und ihre Entwicklung. 1 Theil 136 pp. 2 Theil 148 + xix pp., pls. 1-10. - Cassell. Bibliotheca BOCs. 7. Kamm, Minnie (Watson)., 1922. Studies on Gregarines II. fll Biol. Monographs 7{1): 1-104. 4 pls. Keeble, F., 1910. Plant-animals. A study in symbiosis. ix + 165 pp. Cambridge, University Press. Keeble, F. and Gamble, F. W., 1907. The origin and nature of the green cells of Convoluta roscoffensis. Quar. Jr. Micr. Sei. 51: 167-219, 2 pls. Kessel, J. F., 1923. Experimental infection of rats and mice with the common intestinal amoebae of man. Univ. of Calif. Publ. in Zoology 20(19): 409-450, pis. 58-59. 3 -.- +--+ -- 1924, The distinguishing characteristics of the parasitic amoebae of culture rats and mice. Univ. Calif. Publ. in Zoology. 20(23): 489-544, pls. 43-48, ee es © *.¥ 1926. Trichomoniasis in kittens. . Proc. Soc. Exper. Biol. and Med. 4: 200-202. | 1608LOS Kirby-Smith, J. L., Dove, W. E. and White, G. F., 1926. Creeping eruption. Arch. of Dermat. and Syph. 13: 137-175, 17 figs. Kobayashi, H. 1915. On the life history and morphology of Clonorchis sinensis Centralbl. f. Bakteriol. 1 Abt. 75 - se ee ee 1919. 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