664 TRYPANOSOMIASIS 



portion of flies biting an infective case. Minchin in this connection 

 described in the gut of the fly different types of the parasite, 

 and Koch and Kleine also found in the intestine agglomerations 

 of immature forms which they ascribed to the results of sexual 

 conjugation. The most important fact established by the last 

 observer was, however, that when Gl. morsitans was allowed to 

 bite an animal suffering from nagana it did not become infective 

 for some days. This has been confirmed for Gl. palpalis, in the 

 case of monkeys suffering from Tr. gambiense, by Bruce and 

 those associated with him in 1908-9. Here it was found that 

 infectivity did not appear till about thirty-two days after the fly 

 had fed, and continued until at least seventy-five days. Bruce 

 noted that the renewed infectivity corresponded with the appear- 

 ance of perfect trypanosomes in the salivary gland of the glossina. 

 In this connection certain facts having a serious bearing on the 

 continued infectivity of a locality have emerged. It was found 

 that a certain island on Lake Victoria Nyanza, which had been 

 cleared of infective natives two years previously, still harboured 

 infective flies. To account for this it must be supposed either 

 that the glossina has an extended duration of life, or that the 

 trypanosome exists among the wild animals. It has been found 

 that cattle and wild herbivora. can be infected with the parasite, 

 and can through the medium of the fly infect monkeys. It is 

 possible that such animals, while not suffering in any serious 

 way themselves, are the means of maintaining infectivity. 

 There is no definite evidence that, as Koch supposed, the 

 crocodile harbours the trypanosome. 



Early in the Uganda investigations the question arose as to 

 whether the trypanosome of sleeping sickness was different 

 from Tr. gambiense. This was forced on the inquirers by the 

 fact that a large proportion of the natives in the sleeping 

 sickness area were found to harbour trypanosomes in their 

 blood, although not apparently suffering from the disease. 

 Several cases were carefully examined in which trypanosomes 

 were constantly present in the blcod, but in which the patients 

 from time to time suffered from fever, and during these pyrexial 

 periods trypanosomes were found in the cerebro-spinal fluid. It 

 was suggested that these cases were on the way to develop sleep- 

 ing sickness. A very important observation was that while in 

 sleeping sickness areas a large proportion of the native popula- 

 tion harboured trypanosomes, -this was not the case where sleep- 

 ing sickness did not occur. Further, it was found that 

 trypanosomes from the cerebro-spinal fluid of sleeping sickness 

 cases and from the blood of persons harbouring trypanosomes, 



