THE PATHOGENIC TRYPANOSOMES 545 



ment of its protoplasm and a lashing of the flagellum. The size 

 varies, but those mentioned above are about 30 /x long and about 

 1 '5 to 3 //. broad. From the fact that in progression the flagellum 

 is in front, the flagellated end is denominated the anterior end 

 of the organism. It is stated that the method of examining 

 the fresh blood merely allowed to spread itself out in a 

 fairly large drop beneath a cover-glass is more likely to reveal 

 the presence of trypanosomes, if these are present in small 

 numbers, than is the examination of stained specimens; but the 

 minuter structure of the organisms can best be studied in dried 

 preparations stained by Romanowsky dyes such as those of 

 Leishman or Giemsa. 



For staining trypanosomata (or the Leishman-Donovan bodies) in 

 sections so as to bring out the chromatin structures, Leishman recom- 

 mends the following method: Sections of 5 ft thickness are made and 

 carefully fixed on slides. The paraffin is very thoroughly removed by 

 melting it before applying the first xylol, and then washing with 

 alternate baths of alcohol and xylol three or four times. The last 

 alcohol is thoroughly washed off by distilled water, and the excess of 

 water is removed with cigarette paper. A drop of fresh blood serum is 

 then placed on the preparation and allowed to soak in for five minutes. 

 The excess is removed by blotting, and the remainder is allowed to 

 dry on the section, which is now treated with a mixture of two parts 

 of Leishman's stain and three of distilled water, and placed in a Petri 

 dish for 1 to 1^ hours. The preparation is very deeply stained, the 

 nuclei being almost black and decolorisation and differentiation are 

 effected by alternately applying the acetic acid and caustic soda solutions 

 (commencing with the acid) used in the application of the stain to 

 ordinary histological sections (v. p. 106), the effects .being carefully 

 watched with a low power. The essential part of the method is the 

 application of the blood serum, though what effect this has is not 

 known ; Leishman suggests that it restores the normal alkalinity of the 

 tissue. 



In preparations stained by the above methods the protoplasm 

 of trypanosomata stains blue, and in some species some parts are 

 more intensely coloured than others. Sometimes it contains 

 violet-coloured granules (chromatin granules), and occasionally 

 there appears in it slight longitudinal striation. Two bodies are 

 always present in the protoplasm. Usually near the middle there 

 is an oval granular body staining purple, the nucleus or macro- 

 nucleus, and towards the posterior end is a minute intensely 

 stained purple granule known as the micronucleus or centrosome 

 (that this body represents the centrosome is strongly held by 

 Laveran from the analogy of appearances in certain spermatozoa 

 which closely resemble trypanosomes in structure). This micro- 

 nucleus is often surrounded by an unstained halo, and in its 

 neighbourhood, in certain species, a vacuole has been described 

 35 



