Chapter V: Appendix: On Trematoda and Nematoda 753 (2)

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

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

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

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

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

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

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

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

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

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

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

In opposition to v. Siebold, Küchenmeister successfully proved the necessity of the bladder-worm stage by rearing tapeworms in dogs from the _Cysticercus tenuicollis_ of domestic mammals and from the _Cœnurus cerebralis_ of sheep. He, and simultaneously several other investigators independently, succeeded, with material provided by Küchenmeister, in rearing the _Cœnurus cerebralis_ in sheep from the oncospheres of the _Tænia cœnurus_ of the dog (1854). R. Leuckart obtained similar results in mice by feeding them with the mature proglottides of the _Tænia crassicollis_ of cats (1854).

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

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

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

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

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

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

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

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

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

[8] However, in the Protozoa there are examples of hereditary transmission of parasites, _e.g._, in the case of _Babesia_ (_Piroplasma_) _bovis_ and _Babesia canis_ in their invertebrate hosts (ticks); in _Crithidia melophagia_ and _Crithidia hyalommæ_; and in the case of _Spirochæta duttoni_ in its invertebrate host (a tick).

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

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

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

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

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

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

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

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

LITERATURE.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

JOURNALS.

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

_Annals of Tropical Medicine and Parasitology_, Liverpool.
_Annales de l’Institut Pasteur_, Paris.
_Archives de Parasitologie_, Paris.
_Archives de Zoologie Expérimentale et Générale_, Paris.
_Archiv für Protistenkunde_, Jena.
_Archiv für Schiffs- und Tropen-Hygiene_, Leipzig.
_Bulletin of Entomological Research_, London.
_Bulletin de l’Institut Pasteur_, Paris.
_Bulletin de la Société de Pathologie Exotique_, Paris.
_Bulletins of the Bureau of Animal Industry_, Washington.
_Centralblatt für Bakteriologie und Parasitenkunde_, Jena.
_Compt. Rend. Acad. Sci._, Paris.
_Compt. Rend. Soc. Biol._, Paris.
_Indian Journal of Medical Research_, Calcutta.
_Journal of Experimental Medicine_, New York.
_Journal of Medical Research_, Boston.
_Memorias do Instituto Oswaldo Cruz_, Rio de Janeiro.
_Parasitology_, Cambridge.
_Proceedings of the Royal Society_, London.
_Quarterly Journal of Microscopical Science_, London.
_Review of Applied Entomology_, London.
_Tropical Diseases Bulletin_ (London: Tropical Diseases Bureau).
_Zeitschrift für Infektionskrankheiten_, Berlin.

THE ANIMAL PARASITES OF MAN.

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

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

A. *PROTOZOA*,

BY

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

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

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

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

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

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

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

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

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

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

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

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

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

CLASSIFICATION OF THE PROTOZOA.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

_Order 4._--_Haplosporidia._ Simple organisms, forming simple
spores; they occur in Rotifers, Polychætes, Fish and Man.

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

The orders _Holotricha_, _Heterotricha_, _Oligotricha_, _Hypotricha_
and _Peritricha_ are classified according to the arrangement of the
cilia.

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

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

Class I. *SARCODINA*, Bütschli, 1882.

Order. *Amœbina*, Ehrenberg.

A. *Human Intestinal Amœbæ.*

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

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

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