THE PATHOGENIC TRYPANOSOMES 611 



incut 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 /n broad. Much smaller forms exist, however, 

 and one, 7V. /////''"*, which is 7 to 10 /u, broad and 72 to 123 p. 

 long, has been described by Bruce. 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 by merely allowing 

 it 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 /A 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 alter- 

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

 thoroughly washed oft" 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 Leish- 

 iii, in'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 alter- 

 nately applying the acetic acid and caustic soda solutions (commencing 

 with the acid) used in the application of the stain to ordinary histological 

 sections (r. p. 114), 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 tropho- 

 nucleus or macronucleus, and towards the posterior end is a 

 minute intensely stained purple granule known as the kineto- 

 nucleus, blepharoplast, micronucleus, or centrosome (that this 

 body represents the centrosome is strongly held by Laveran 

 from the analogy of appearances in certain spermatozoa which 



