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sometimes markedly thickened. In Giemsa preparations there is often 
a small granule at the point of emergence of the flagellum : this does 
not appear in staining with iron-haematoxylin, and is perhaps due to a 
deposit of the Romanowsky stain. The rhizoplast and flagellum are 
very much thicker in Giemsa than in iron-haematoxylin preparations: 
with regard to the flagellum, the Giemsa certainly gives the proportions 
more as they are in life. The kineto-nucleus is a tongue-shaped or rod¬ 
shaped body, placed about Q/j, from the anterior end. In Giemsa 
preparations it is very large and conspicuous, measuring as much as 
it stains a dark rich red, in the midst of which it is usually 
possible to make out a more deeply-staining central body. With iron- 
haematoxylin (figs. 24 and 25), the kineto-nucleus appears smaller, 
stains uniformly and tends to be circular or rod-shaped, rather than 
tongue-shaped. The tropho-nucleus lies posterior to the kineto-nucleus, 
about half-way along the body. It is oval or roughly circular, measuring 
about 3 n x 2/r. In Giemsa preparations it stains pinkish-red, and almost 
always appears to consist of a fine reticulum on which small chromatin 
granules are distributed. Iron-haematoxylin gives a very different 
picture: here the stain is mainly taken up by the central karyosome, 
and there is a well-marked nuclear membrane; sometimes there is a 
faint net-work suggested between the karyosome and the membrane, 
but of chromatin granules there is no hint. In Giemsa preparations the 
cytoplasm stains a clear blue, tinged with purplish in places, and fading 
into pink in the neighbourhood of the flagellum and kineto-nucleus. 
Occasionally vacuolated areas appear, and nob infrequent, especially in 
the smaller flagellates, is a clear sinuous line visible between the kineto- 
and tropho-nuclei and descending thence into the posterior part of 
the cell. This line corresponds in position-with the spiral “Doppelfaden” 
described by Prowazek in H. muscae-domesticae, but I never succeeded 
in staining it, and am quite at a loss as to its true nature. I have 
never seen any hint of a cytostome in these flagellates, and am not 
inclined to regard it as an “ intestinal canal 1 .” After Giemsa’s stain the 
cytoplasm appears full of deeply-staining, chromatin-like granules, 
especially numerous in the region posterior to the tropho-nucleus. 
That these are not composed of chromatin, however, is well seen on 
staining with iron-haematoxylin, which the cytoplasm takes on very 
uniformly, showing a hint indeed of reticular structure but very rarely 
containing anything that could be called granules. It is probable that 
1 Cf. Leger (1902), Covipt. rend. Acad. Sc., cxxxiv. p. 781. 
Parasitology hi 
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