The Project Gutenberg eBook of The Animal Parasites of Man, by H. B. Fantham, J. W. W. Stephens and F. V. Theobald.

A row of twelve or more cilia was said to commence at the anterior end and extend over the body. Leuckart stated that this parasite, placed by the two authors in the genus Cercomonas, was a Trichomonas, and that they mistook the undulating membrane for cilia, and overlooked the flagella. Notwithstanding its striking similarity with T. vaginalis, it was said to be distinguishable from that species by differences in the undulating membrane. Lambl’s C. intestinalis38 (of 1875) which corresponds with C. hominis, Davaine39 (1854), is regarded by Leuckart as a true Cercomonad (characterized by a flagellum and the absence of an undulating membrane, see p. 61), and is thus generically distinct from Trichomonas.

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

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

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

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

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

The genus Tetramitus differs from Trichomonas in possessing an undulating membrane inserted in a deep groove or cytostome. There are three anterior flagella. The pear-shaped organism measures 14 µ by 7 µ, but smaller examples occur. T. mesnili occurs in the human intestine, having been described by Wenyon43 (1910) from a man from the Bahamas in the Seamen’s Hospital, London. Its occurrence is widespread. Alexeieff considers that Macrostoma and Tetramitus are synonymous. The parasite is the same as Fanapapea intestinalis, Prowazek, 1911, from Samoa. Brumpt (1912) found T. mesnili to be the causal agent of colitis in a Frenchwoman. Nattan-Larrier (1912) considers it of little pathological importance.

Gäbel44 (1914) described an interesting case of seasonal diarrhœa acquired in Tunis, in which a new Tetramitid was the causal agent. The organism was pear-shaped, without an undulating membrane, and measured 6·5 µ to 8 µ by 5 µ to 6 µ. The cytostome was large, and there was no skeletal support. Encystment occurred. Gäbel named the organism Difämus tunensis and considered that it was pathogenic.

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

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

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

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

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

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

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

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

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

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

In Upper Italy the parasite in the encysted condition has also been seen by Perroncito in man. At the same time, Grassi and Schewiakoff began a new investigation of specimens from mice and rats. In Germany, L. intestinalis was found by Moritz and Hölzl, Roos, Schuberg and Salomon. Moritz and Hölzl confirmed the relative frequency of the species. In Königsberg, Prussia, a student found encysted Lamblia in his fæces. One case was reported from Finland by Sievers, another case from Scandinavia by Müller. Frshezjesski and Ucke reported cases from Russia. Jaksch announced the occurrence of the parasite in Austria; Piccardi mentioned their presence again in Italy. They were reported from Egypt by Kruse and Pasquale, and from North America (Baltimore) by Stiles. Noc stated that 50 per cent. of the population of Tonkin harboured Lamblia. Finally, the structure of L. intestinalis has been described by Metzner (1901), and by Wenyon46 (1907) in mice.

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

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

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

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

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

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

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

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

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

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

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

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

Perroncito and Piccardi have described encysted stages of Cercomonads.

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

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

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

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

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

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

Hassall47 in 1859 first found Bodo-like flagellates in human urine. He examined fifty samples of urine from patients suffering from albuminuria and from cholera. The reaction of the urine was alkaline or sometimes only feebly acid. The flagellates were only seen after the urine had been standing for several days. Hassall named the organism Bodo urinarius, and gave a very good description of it with illustrations. The flagellate, which was round or oval, measured 14 µ by 8 µ. The organism had “one, usually two, and sometimes three lashes or cilia.” In 1868 Salisbury described a similar flagellate in the urine under the name Trichomonas irregularis. Künstler in 1883 described the latter parasite under the name B. urinarius. In 1885 Blanchard, considering Künstler’s organism a different parasite from Hassall’s, called it Cystomonas urinaria. Braun, in 1895, gave the name Plagiomonas urinaria. Barrois (1894) considered Künstler’s and Hassall’s organisms to be identical and not to be true parasites of man. Sinton,48 in 1912, found the flagellate in the deposit, after centrifuging, of a 24-hour old specimen of alkaline urine from a Mexican sailor in the Royal Southern Hospital, Liverpool. Sinton found a kinetic nucleus or blepharoplast in the organism, and therefore placed it in the genus Prowazekia.

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

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

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

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

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

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

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

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

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

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

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

Historical.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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