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X] Etiology.——In common with other trypauosomes, T. gambiense, as seen in fresh blood, is an active, wriggling organism, having a spindle-shaped body, which is slightly compressed laterally. It is provided with a delicate, wavy membrane——the undulating membrane——which fringes the convex dorsal edge of the body, and terminates in a free, whip-like filament, the flagellum. Suitably stained specimens show a nucleus about the centre of the body, and a minute, deeply staining chromatin mass, the blepharoplast (kinetonucleus), generally near one pole. The extremity of the body which encloses the blepharoplast is regarded by recent authorities as the posterior extremity; it varies greatly in shape and may be pointed or obtuse. The opposite end, the anterior extremity, tapers to a point, to which the flagellum is attached. Adjoining or surrounding the blepharoplast is a small non-staining area, the vacuole. The free border of the undulating membrane is somewhat thickened; this thickened border springs from the blepharoplast at one end, and its continuation at the other constitutes the flagellum. In certain specimens the cytoplasm is homogeneous; in other specimens comparatively faintly staining granules are visible. In comparing and measuring a large series of specimens, it becomes apparent that there is great diversity in the dimensions of the body of the parasite, the nucleus, and the flagellum (Fig. 46). Thus, some are short and stumpy, with short or no flagellum, measuring from 14 to 20 μ in length; others are long and slender 23 to 33 μ; others again are of intermediate dimensions 20 to 24 μ in length by 1.40 to 2 μ in breadth. In certain instances evidences of multiplication by longitudinal division are seen. The process commences most frequently in the blepharoplast, which elongates, and then divides. The nucleus divides almost simultaneously, sometimes before the blepharoplast. The division of the blepharoplast is followed by the duplication of the thickened margin of the undulating membrane, beginning at its blepharoplast attachment; this, in its turn, is followed by longitudinal division of the whole body. According to Miss Muriel Robertson an accomplished protozoologist working in Uganda——only a portion of the flagellum is split off with the daughter individual. The fission of the body is effected dorso-ventrally,