396 MICROBIOLOGY 



dish, or better, a square or oblong dish with sloping bottom. The 

 slide on which the blood-film has been spread and fixed is placed 

 film downwards in the staining solution (a piece of glass rod or a 

 projection from the bottom of the dish preventing the slide from 

 touching the bottom, where a precipitate nearly always forms), and 

 left there for five to twenty minutes. Five to ten minutes' staining 

 is long enough for most trypanosomes, especially for the mammalian 

 parasites; twenty minutes' staining is necessary for certain species 

 e. g., T. Lewisi particularly when undergoing reproduction. After 

 removal from the staining solution the slide is well washed in a 

 large quantity of water (or by blowing a strong stream of water on 

 the film with a wash-bottle), then treated with the solution of tannin 

 for several minutes, again washed in excess of water, and finally in 

 distilled water, and dried. If a precipitate is formed, which would 

 render microscopical examination difficult, wash the film with oil 

 of cloves, then with xylol, and gently rub the surface of the prepara- 

 tion with a piece of soft linen soaked in xylol. 



The preparations keep better uncovered than if covered with 

 balsam or cedar-wood oil, in which case they rapidly lose their stain. 

 When the staining has been successful, the protoplasm of the para- 

 site is pale blue; the nucleus, fiagellum, and edge of the undulating 

 membrane are purplish; the centrosome is deep violet a little dif- 

 ferent from the nucleus; the undulating membrane is unstained, or 

 stained a very pale blue. The red corpuscles are pink, the nuclei of 

 the leucocytes dark purple. 



TRYPANOSOMA EVANSI STEELE. 



Place in nature. Trypanosoma Evansi is the cause of the 

 disease in horses, cattle and occasionally in dogs, elephants and 

 other wild animals, known as surra. The name "cachectic" 

 was given by natives to this disease which in horses is char- 

 acterized by a profound cachexia and has been known for a 

 great many years. It closely resembles nagana in that its es- 

 sential lesion is that of anemia with remittent and intermittent 

 fever; edema of the limbs and abdomen, great muscular 

 weakness and terminal paresis. This disease lasts from one to 

 several months. Occasionally it runs its course more quickly. 

 This trypanosome was discovered by Evans x in 1880. In 

 1885 Steele 2 identified the one found in transport mules in 



1 Evans. Report on Surra, Military Dept, Dec. 1880. 



2 Steele. Report on an obscure and fatal disease in transport 

 mules, etc., 1885. 



