TRYPANOSOMA 



385 



When the parasites are present in the peripheral blood, they 

 usually show a marked pleomorphism. Thus, in T. castellanii Miss 

 Robertson finds short forms 14 to 20 in length, medium forms 

 20 to 24 fj^ in length, and long forms 23 to 33 /x in length. Until 

 recently it was usual to consider these variations as being probably 

 indicative of sexual differentiation, but she concludes that this is not 

 so, but that they are variations due to different stages of growth 

 and subsequent division. The multiplication of the trypanosome 

 in the blood is usually by longitudinal fission, but it may also take 

 place by schizogony, with or without entering an endothelial or 

 other cell. The number of trypanosomes in the blood varies con- 

 siderably from time to time, apparently in more or less regular 

 cycles, and their disappearance appears to be associated with the 

 encystment in the lungs, spleen, bone-marrow, etc., in the form of 

 the latent bodies described by Breinl, Fantham, and others. During 

 their life in the vertebrate it was, at one time, thought that they 

 could propagate their species — in part, at all events — by granules, 

 which are comparable to the ' infective granule ' described by 

 Balfour for spirochsetes, because Fry demonstrated that T. brucei 

 could throw off granules, and his observations had been confirmed 

 by Ranken. This granule-shedding was described as taking place 

 in the liver, spleen, lungs, and lymphatic glands. At first the 

 granule was simply a free pyriform body, but later it developed a 

 flagellum and became actively motile . Its further history was, how- 

 ever, untraced in tr^^panosomes. 



There can be no doubt that there is a reaction on the part of the 

 cells of the vertebrate against the trypanosomes with the formation 

 of antibodies in the form of trypanolysins, etc., but more will be 

 said on this subject later. 



Binary Fission. — A binary fission takes place with or without 

 growth. This is brought about by amitotic division of the kine- 

 tonucleus and trophonucleus, followed by the formation of a 

 new flagellum in the daughter parasite and the division of the 

 cytoplasm. 



The details of the division are as follows : — 



1 . The kinetonucleus swells up and forms a vesicle through which 

 the chromatin is evenly distributed. 



2. The chromatin forms a band across the middle of the vesicle. 



3. The band elongates and divides into two portions. 



4. The two portions move apart, all trace of the vesicle disappears, 

 and the two new kinetonuclei are formed. 



5. The blepharoplast divides at the same time as the kineto- 

 nucleus. 



6. Either the old flagellum divides or a new flagellum develops 

 from one of the new blepharoplasts. The process varies in different 

 species. 



7. The central karyosome of the trophonucleus either divides 

 and the two portions move to opposite poles of the nucleus, but are 

 connected by a fine line, or the chromatin forms an equatorial plate, 



25 



