28 NATURAL HISTORY OF SLEEPING SICKNESS 



flies on the island acquired the cause of Sleeping 

 Sickness. 



This discovery made the question of the return of the 

 natives to the lake shore a far more difficult one than 

 was anticipated when they were removed during the 

 height of the epidemic. It was then thought that as the 

 fly was merely a mechanical carrier of the Trypanosome, 

 an interval during which all known sources of infection 

 (the natives) were kept away from the fly would allow 

 the disease to die out, and when the life of the infected 

 flies had come to an end, the natives who were free from 

 Trypanosomes could return without danger. But now 

 that it is known that there is a " vicious circle," the 

 fly acquiring the Trypanosome from the antelope and 

 in turn inoculating it into fresh animals, the islands and 

 mainland shore of the lake are still dangerous. It is 

 true that some consider that it is possible that the 

 Trypanosome has been for so long away from man's 

 blood that it may no longer be pathogenic to him, 

 but against this is the fact that as a result of living on 

 the islands with me in 1911-12 three of my native 

 employees were found to be infected when I examined 

 them before returning to the islands in 1914, and one at 

 least is reported to have died. 



So far as we know at present, the fly would be harmless 

 without the antelope and the antelope without the fly, 

 and to eliminate the disease from the most fertile and 

 beautiful part of Uganda these two must be kept apart ; 

 that is to say, one of them must be exterminated. 



In 1914 I obtained most interesting confirmation of 

 Dr. Duke's results. The Island of Nsadzi, lying opposite 

 to Entebbe and south of it, was well populated in the old 

 days, and there was very little refuge for Enjobe there ; 

 I was told by my canoe-men that the antelope was not 

 to be found on the island in those days. In 1911 the 

 flies on Nsadzi were tested and were found to be free 



