1082 PATHOGENIC PROTOZOA 



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 

 carrier, but it is more probable that a cyclical development of the 

 parasite takes place in the fly, after which it remains infectious for 



D 



FIG. 136. THE MOST IMPORTANT TRYPANOSOMES PARASITIC IN VERTEBRATES. 

 A, Tr. lewisi; B, Tr. evansi (India); C, Tr. evansi (Mauritius); D, Tr. brucci; 

 E, Tr. equiperdum; F, Tr. equinum; G, Tr. dimorphon; H, Tr. gambiense. 

 (X1500.) (From Doflein after Novy. MacNeal, " Pathogenic Microor- 

 ganisms," published by P. Blakiston's Son & Co.) 



a long period. It has been shown that after the first few hours 

 the fly is not infectious again until the lapse of eighteen days, when 

 its bite once more conveys the disease, and trypanosomes may be 

 found in the intestinal canal, the body cavity, the salivary glands 

 and in the proboscis. Studies of the cycle in the fly show that 

 only about five per cent of the flies permitted to feed on sick animals 

 become chronic carriers. The work of Bruce and others has shown 

 that the trypanosomes are more or less harmless parasites of the 

 big game animals of Africa, which therefore are believed to act 

 as a reservoir, from which the disease is transferred to the domestic 



