TRYPANOSOMA OF SLEEPING SICKNESS 627 



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. In this connection certain facts 

 having a serious bearing on the continued infectivity of a local- 

 ity 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. As it has been found that cattle may be infected with 

 the parasite, and may through the medium of the fly infect 

 monkeys, it is possible that wild herbivora, 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 trypanosoma of sleeping sickness was different from 

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

 that a very 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 blood, 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, 

 but not suffering from disease symptoms, gave rise in monkeys 

 to the same group of chronic effects which resembled the last 

 .stages of the disease in man. These facts led the Commissioners 

 to incline to the idea that trypanosoma fever and sleeping sick- 

 ness are due to the same cause, and represent different stages 

 <f the same disease. It has already been pointed out that a 

 fatal termination can occur in trypanosoma fever by an acute 

 febrile attai-k or from intercurreut disease, and thus the terminal 

 lethargic stage may only develop in a certain proportion of cases. 

 Continued observation of prolonged cases of trypanosoma fever, 

 -both in Uganda by Greig and Gray, and in this country by 



