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TRYPANOSOMA. 17 



a clean cover-glass and invert this over a bottle of glacial acetic 

 acid. The acetic vapour will kill and fix the cells in a few 

 minutes. Dry gently over a flame, cover the film so produced 

 with weak hematoxylin or methyl-blue-eosin. Allow the stain to 

 act for five minutes. Wash with water and mount in glycerine or 

 dehydrate with successively strong grades of alcohol, clear with 

 cedar wood oil, and mount in Canada balsam. 



A. General Appearance and Structure. 



Trypanosoma consists of an elongated cell (90 /jl in length) 

 produced at one end into a whip-like ' tail ' 

 (flagellum) and lies coiled up in the blood plasma, but 

 is continually agitated by a wave-like movement of the 

 ' undulating membrane ' that projects from one side 

 of its body. No mouth or contractile vacuole is present. 

 Nutrition is carried on by osmosis through the delicate 

 pellicle. The cell consists of ectoplasm, endoplasm, 

 and nuclear bodies, v , 



Two nuclei are present. The tropho-nucleus ' consists 

 of a lens-shaped mass placed near the centre of the 

 body. The much smaller ' kineto-nucleus ' lies in 

 front of ohis, and from it is given off the * flagellum' 

 Which runs down the side of the body, following a 

 tortuous course, and attached by the undulating mem- 

 brane for the greater part of its length, but finally 

 emerging freely. 



B. Reproduction. 



Fission is the only means of reproduction that is at present 

 known to occur 



C. Life-history. 



Trypanosomes are usually carried from one host to another 

 by an invertebrate that sucks the blood of the infected 

 host and then, after cultivating the parasite for a time 

 in its own body, infects the new host by its bite or in 

 other ways. In the case of fish-Trypanosomes the 

 carrier is a leech, but the life-history of the dogfish 

 Trypanosome is not yet worked out. 



