Page:EB1911 - Volume 27.djvu/359

observations to hand which shew that piscine, amphibian and mammalian Trypanosomes may also become attached. Probably most forms possess a resting, attached phase at some period or other, in the invertebrate, if not in the vertebrate host.

Considering now the Trypanosomes in an unaccustomed, mammalian host, they may either remain infrequent or rare (sometimes, indeed, being unnoticed until shortly before death), or, on the other hand, they may soon become numerous and go on increasing (fig. 2). In the latter case the disease is acute and rapidly fatal; in the former it is more chronic and lasts much

longer, often several months.

(After Dofleln.)

Fig. 2.—Trypanosoma equiperdum (of dourine), in the blood of a rat eight days after inoculation.

a, Parasites.

b, Blood-corpuscles.

The main features of trypanosomosis, or illness caused by a Trypanosome, show a general agreement, whichever variety is considered; one symptom may be, of course, more marked than another in any particular case. Death is due either to weakness and emaciation (in chronic cases), or to blocking of the cerebral capillaries by the parasites (where these are abundant), or to disorganization of the nervous system (paraplegic and sleeping sickness cases).

In post-mortem examination, the most obvious pathological lesion is hypertrophy of the spleen, which may be very pronounced; the lymphatic glands in the neck, inguinal region, &c., are also often greatly swollen. These are undoubtedly the organs which react most strongly to the parasites, and their enlarged condition is to a great extent due to their enhanced activity in elaborating blood-corpuscles and leukocytes to cope with the enemy. Ingestion and dissolution of the Trypanosomes by phagocytes has frequently been observed; and it is probable also that the haematopoietic organs secrete some substance which exerts a harmful action on the parasites, and causes them to undergo involution and assume weird-looking “amoeboid” and “plasmodial” forms.

A peculiar feature in the behaviour of the parasites, which is most probably caused by unfavourable biological conditions in the host, is that known as agglomeration. The process is readily brought about artificially by the addition of sera or chemical solutions to blood containing the parasites. Agglomeration consists in the grouping or union together of several Trypanosomes around a common centre; this leads to the formation of rosette-like clusters, or even of large masses composed of several rosettes. The end by which the parasites join is typically, in the case of Trypanosoma, the non-flagellate (anterior) end. If a favourable change in the surrounding medium sets in, the Trypanosomes are able to undergo the reverse process, namely dis agglomeration; the parasites liberate themselves and the rosette is dissolved.

Trypanosomes vary greatly with regard to size; even in one and the same species this variation is often noticeable, especially under Mon, , w, oD, different conditions of life. The common Trypanosoma rotatorium of frogs (fig., A and B) is, taking it all in all, one of the largest forms so far described. Its length (inclusive of the flagellum) varies from 40-60 p, while its greatest width (including the undulating-membrane) is from 8-30, a; in the very wide individuals breadth is gained more or less at the expense of length. Conversely, T. gambiense, the human parasite (fig. 3 C), is gne C; the smallest forms known, its average size being about 21–23 μ by 11/2–2 μ.

There is equally great diversity in respect of form. Typically, the body is elongated and spindle-shaped; it is usually more or less curved or falciform (fig. 3, A-D), and tends to be slightly compressed laterally. It may be, however, anything from extremely slender or vermiform (fig. 3, H) to squat and stumpy (fig. 3, G, 4, A). Moreover, apart from the fact that a full-grown adult, ready to divide, is in many cases much plumper than a young adult (cf. T. lewisi, fig. 6, A and B), there can be no doubt that considerable polymorphism also sometimes occurs (e.g. T. rotatorium). In many cases, at any rate, this indicates a difference in sexuality; and it is particularly necessary to bear this factor in mind when considering the avian Trypanosomes, where, perhaps, the extremes of form are to be met with. 'That one and the same species may appear entirely different in different phases of the life-history is manifest on comparing, for instance, the chief “forms” of Trypanosoma

FIG. 3.-Representative Mammalian, Avian and Reptilian Trypanosomes, to illustrate the chief morphological characters.

A, Trypanosoma lewisi, after Bradf. and Plimmer.
B. T. brucei, after Lav. and MesniL
C. T. gambiense (blood, T-fever), after Bruce and Nabarro.
D. T. equinum, after Lav. and Mesnil.
E, Trypanamorpha (Trypanosoma) noctnae, after Schaud.
F. Trypanosoma avium, after Lav. and Mesnil.
G. Hanna's Trypanosome from Indian pigeons.
H. T. ziemanni, after Schaud.
J. T. damonia, after Lav. and Mesnil.
c.g, Chromatoid grains; v, vacuole; Ls, fold or striation.

ziemanni described by Schaudinn. The asexual or indifferent type (fig. 3, H) is extremely thread-like, greatly resembling, in fact, a Spirochaete; on the other hand, both male and female individuals have the form of a very wide spindle.

In Trypanoplasma and T rypanophis there are two flagella, inserted into the body very close to the anterior end (fig. 4, F and G). One flagellum is entirely free and directed forwards; the other at once turns backwards and is attached to the convex or dorsal side of the body for the greater part of its length. In all other Trypanosomes there is only one Hagellum, which is invariably attached to the body in the same manner as the posterior one of bi flagellate forms. This flagellum, however, is most probably not to be considered homologous in all cases. (See Woodcock, loc. cit.)

In Trypanomorpha (fig. 3, E), which is to be derived from a Herpetomonadine type, the single, anterior flagellum of the ancestral parasite has been drawn backwards along one side of the body and now originates in the posterior half. Hence in this genus the end beari ng the free part of the Hagellum is the anterior one. The genus Trypanosoma, in which are included at present the great majority o Trypanosomes, is rather to be regarded as derived from a Heteromastigine ancestor, such as Trypa-noplasma, by the loss of the anterior flagellum. Hence in this type the single flagellum represents the posteriorly-directed one of Trypanoplasma, and the end at which it becomes free is the hinder end. The point of origin of the flagellum in Trypanosoma is usually near the anterior end, but may vary considerably (cf. figs); and its free portion may be very short or lacking.

Along the dorsal side runs the characteristic fin-like expansion of the body, the undulating-membrane, which is the organelle principally concerned in locomotion. This always begins at the place where the attached flagellum emerges from the body; and its free edge is really constituted by the latter, which forms a flagella border. The membrane is usually more or less sinuous in outline, and is sometimes thrown into broad folds (fig. 3, F and ]). Distally it thins away concurrently with the body. .