LIFE CYCLE OF TRYPANOSOMES 



25 



monkey in a proportion of cases also showed the Trypano- 

 some in its blood. Control experiments showed that a 

 freshly hatched fly contains no Trypanosomes, so that 

 those in the above experiments must have acquired them 

 from the first monkeys fed upon. 



The two diseases Nagana and Sleeping Sickness are 

 thus entirely parallel, as is shown by the following table : 



It has been said that the transmission of the Trypano- 

 some of Nagana was believed to be entirely mechanical, 

 and for some years this was also thought to be the case 

 with T. gambiense. With further knowledge, however, 

 it became clear that there was a period after the fly 

 had fed during which the Trypanosome could not be 

 transmitted to a fresh animal. It had previously been 

 supposed that this was because the Trypanosome was no 

 longer alive in the fly, but KJeine, working in German 

 East Africa, showed in 1908 that the non-infectivity of 

 the fly after a few days did not mean the death of the 

 Trypanosome, but that it was going through a cycle of 

 development in the alimentary canal of the fly, and was 

 not in an infective condition. For when the develop- 

 ment was complete Kleine found that the fly could 

 convey the disease fifty days after it had acquired the 

 Trypanosome. These most important results were fully 

 confirmed in Uganda in 1909 ^ and it was found that the 

 time required for the cycle of development in tha fly 



* Reports of the Sleeping Sickness Commission, vol. x, p. 46, etc. ; 

 vol. xi. p. 12, etc. 



