746 



PATHOGENIC PROTOZOA 



Morphology. Morphologically, it resembles closely most of the 

 other pathogenic trypanosomes, and Minchin makes it the. type of a 

 group of pathogenic trypanosomes, all closely resembling one another 

 and possibly descended from one common ancestor : the group consists 

 of brucei, gambiense, evansi, equiperdum, rlwdesiense, and hippicum. 

 The organism is less slender than lewisi and has a wider undulating 

 membrane. The posterior end is relatively short, the trophonucleus 

 lies in the middle of the body and the kinetonucleus at the extreme pos- 



a 



FIG. 170. THE MOST IMPORTANT TRYPANOSOMES PARASITIC IN VERTEBRATES. A, 

 Tr. lewisi; B, Tr. evansi (India); C, Tr. evansi (Mauritius); D, Tr. brucei; E,Tr. 

 equiperdum; F, Tr. equinum; G, Tr. dimorphon; H, Tr. gambiense. (X 1500.) 

 (From Doflein after Novy. MacNeal, "Pathogenic Microorganisms," published 

 by P. Blakiston's Sons & Co.) 



terior end; a vacuole is placed just in front of the latter. In length 

 the parasite measures twenty-five to thirty-five microns and is one and 

 a half to two and a half microns in width ; multiplication in the blood 

 stream is by binary fission. 



Transmission is by means of the tsetse fly, Glossina morsitans, and 

 perhaps Glossina pallidipes and Glossina fusca. The fly may transmit 

 the disease directly after infection, acting as a mere mechanical car- 

 rier, but it is more probable that a cyclical development of the para- 

 site takes place in the fly, after which it remains infectious for a long 



