Page:EB1911 - Volume 27.djvu/362

 complicated nuclear changes and divisions undergone by Trypanosomes; these are considered, in many cases, to represent some kind of parthenogenesis.

A very interesting modification of the life-cycle of a Trypanosome which must be mentioned has been made known by Minchin, in his account of T. grayi, in a tsetse-fly (G. palpalis). Unfortunately the vertebrate host of this form is not yet known. Certain individuals of a particular character form definite rounded cysts in the rectum of the fly; in this condition, the only sign of Trypanosome structure is afforded by the two nuclei, which remain separate. These cysts are doubtless for dispersal by way of the anus, and the vertebrate host is in all likelihood infected by the mouth and alimentary canal. This reveals a quite novel mode by which infection with a Trypanosome may be brought about; so far, however, T. grayi remains the only known example.

As remarked in the section on morphology, the Trypanosomes as a whole are preferably regarded as including two entirely distinct groups, Monadina and Heteromastigia.

Family: Trypanomorphidae, Woodcock.-Haemoflagellates derived from a unifiagellate, Herpetomonadine form, in which the int of insertion of the single (anterior) flagellum into the body figs travelled backwards from the anterior end for a greater or less distance, the flagellum itself having become, concurrently, attached to the body for a portion of its length by means of an undulating membrane.

Genus Trypanomorpha, Woodcock, 1906.—With the characters of the family. The only species yet known is the type species, T. noctuae (Celli and San Felice). [Syn. Trypanosoma n. (C. & S.F.), Schaud.=Halteridium n. (C. & S.F.)]. See figs. 3, E, 7. Vertebrate host, Athene noctua, Little Owl; invertebrate host, Culex pipiens.

There are, in addition, other forms, which are probably to be laced in this family, but which are not yet sufficiently well known For their systematic position to be settled. It is, for instance, quite likely that certain Herpetomonadine parasites described by Leger (29, 34) from various blood-sucking insects are really only stages in the life of a Haemoflagellate. Some of these are placed by Léger in a newly discovered genus, Crithidia.

Family: Trypanosomatidae, Doflein.-Flagellates, in the great majority of instances haemal parasites, derived from a bi flagellate, Buda-like type, in which the posteriorly-directed (trailing) flagellum is always present and attached to the body by an undulating membrane, of which it constitutes the thickened edge. The other, the anterior flagellum, may or may not persist.

Genus Trypanoplasma, Lav. and Mesnil, 1902.—The anterior flagellum is present. Both flagella are inserted close together, near the anterior end of the body. Two sub-groups may be' distinguished. In one, exemplified by T. borreli (fig. 4, F and G) from the rudd and minnow, the anterior flagellum is well-developed, and the free parts of both are of about equal length. In the other, exemplified by T. cyprini (fig. 4, H) from carp, the anterior flagellum is much shorter than the free part of the posterior one, and evidently tending to disappear. Known invertebrate hosts for different species are Hemiclepsis and Piscicola, leeches.

Genus Trypanophis, Keysselitz, 1904.—The body resembles that of Trypanoplasma in general appearance, but the locomotor apparatus does not appear to be so well-developed, especially in T. grobbeni. The anterior flagellum is longer than the free part of the posterior one. The species included are not, so far as is known, haemal parasites. T. grobbeni occurs in the coelenteric cavity of various Siphonophora.

An interesting form, “Trypanoplasma” intestinalis, which resembles both the above genera, occurs in the alimentary canal of Box boops. Probably this is not a haemal parasite, and lacks an alternate host.

Genus Trypanosoma, Gruby, 1843.—(Principal synonyms: Undulina, Lank., 1871; Herpetomonas, Kent, 1880, only in part; Pafamoecioides, Grassi, 1881; Haematomonas, Mitrophan, 1883.) There is no anterior flagellum. The point of insertion of the attached (posterior) flagellum into the body, and, consequently, the commencement of the undulating membrane may be almost anywhere in the anterior half of the body, but is usually near the extremity.

Among the more important and better-known forms are the following:—

Parasitic in mammals: T. lewisi (Kent), the well-known natural Trypanosome of rats (figs. 3, A, 6, A); T. brucii, Plim. and Bradf., the cause of nagana among cattle, horses, &c., in South Africa (fig. 3, B); T. evansi, Steel, the cause of surra to horses in Indo-Burmah; T. equiperdum, Dofl., the cause of dourine in horses in Algeria and other regions of the Mediterranean littoral; T. equinum, Voges, causing mal de caderas or “hip-paraplegia” in South America (fig. 3, D); T. theileri, Lav., a very large form, the cause of galziekté or bile-sickness to cattle in the Transvaal; and T. gambiense, Dutton (syn. T. ugandense, Castellani, T. castellanii, Kruse), the cause of human trypanosomosis in central Africa, which becomes sleeping-sickness when the organisms penetrate into the cerebro-spinal fluid (fig. 3, C).

Parasitic in birds: T. avium (Danil., Lav. emend.), probably the form to which Danilewsky’s original investigations related, parasitic in owls and (according to Novy and McNeal) also in other birds (fig. 3, F); ''T. Johnstoni'', Dutt. and Todd, a very spirochaetiform type, from little birds (Estrelda) in Senegambia; and Hanna’s peculiar wide species from Indian birds, with a remarkably tapering anterior end (fig. 3, G). Lastly, there is T. ziemanni, Lav., [syn. Spirochaete z. (Lav.), Schaud, “Haemamoeba” z., Lav., the “Leucocytozoon” of Danil.], from various owls, and Culex pipiens, whose life-history has been described by Schaudinn (fig. 3, H). (As above mentioned, this form may not be a true Trypanosome.)

Only one reptilian form is well known, T. damoniae, Lav. and Mesn., from a tortoise, Damonia feevesii (fig. 3, ]). Parasitic in batrachia: T. rotatorium, Mayer (syn. Amoeba r., Mayer, July 1843, T. sanguinis, Gruby, November 1843, Undulina ranarum, Lank., 1871), the best-known parasite of frogs, which exhibits remarkable polymorphism (fig. 4, A and B); T. mega and T. karyozeukton, Dutt. and Todd, even larger than T. r. (fig. 4, D), with peculiar cytological differentiation, may be only sub-species; T. inopinatum, Sergent, and T. nelspruitense, Lav., also from frogs (fig. 4, C). Parasitic in fishes: T. remaki, Lav. and Mesnil, from pike, a relatively small form (fig. 4, L); T. barbatulae, Léger, from loach; T. granulosum, Lav. and Mesnil, a very long vermiform parasite, from eels (fig. 4, K); T. soleae, Lav. and Mesnil, from soles, with a relatively small flagellum (fig. 4, ]); and T. scyllii and T. rajae, from those Elasmobranchs, both very large forms, described by Lav. and Mesnil.

Undoubtedly closely allied to the Haemofiagellates, although no actual trypaniform phase has yet been observed, are the important parasites usually known as the “Leishman-Donovan” bodies, without some consideration of which an account of the Haemoflagellates would hardly be complete. These bodies are constantly found in certain tropical fevers (e.g. dum-dum fever, kala-azar) particularly prevalent throughout Indo-Burma, of which they are generally held to be the cause. They were discovered by W. Leishman in 1000, but before his first account of them (36) was published they were also seen quite independently by C. Donovan. Moreover, organisms very similar to these (morphologically, indeed, the two sorts appear scarcely distinguishable) are found in various sores or ulcers (e.g. Delhi boil, Oriental sore, “bouton d’Alep”) to which people in different parts of the East are liable. These were first described by J. H. Wright (58).

The chief distinction between the parasites in the two cases is in their habitat. In the one case they are entirely restricted to the neighbourhood of the boil or ulcer, whereas in the other there is a general infection of the body, the organisms spreading to all parts and being met with in the spleen, liver, bone-marrow, &c., and (rarely) in the peripheral circulation. The parasites are either free or intracellular. In the latter case they invade cells of a leucocytic or phagocytic character as a rule; Leishman’s form is particularly abundant in large macrophageal cells originating from the vascular endothelium of the spleen (fig. 8, I. M).

The parasites themselves are very minute and usuall ovoid or pyriform in shape (fig. 8, I. a), the latter being, perhaps, tire most typical. The splenic type is somewhat smaller than Wright’s parasite; the former, when pear-shaped, is from 3 to 4 in length by 1 to 2 in width, the latter being about 4 by 3  (fig. 8, III.). The body is probably not limited by any distinct membrane. The cytoplasm is finely granular and fairly uniform in character. The most interesting point about the morphology is the fact that two chromatic bodies, of very unequal size, are almost invariably to be recognized. The larger nuclear body, which corresponds to the trophonucleus of a Trypanosome, is usually round or oval; the smaller one, representing a kinetonucleus, has the form either of a little rod or of a round grain, and is generally separate from the larger nucleus.

The parasites multiply in two ways—(a) by binary fission, and (b) by multiple division or segmentation. The principal stages in the first method are well known (fig. 8, I. b); they offer strong resemblance to the process in Piroplasma. Multiple division has not yet been so satisfactorily made out. It appears to conform more or less to the radial or rosette type of multiplication, enlarged rounded parasites, with a varying number of nuclei (up to about eight) uniformly arranged near the periphery, having been often noticed (fig. 8, I. c and IV. b). The details of the process are somewhat differently described, however, by different observers.

Laveran and Mesnil (27) gave the name Piroplasma donovani to