62 Sleeping Sickness in Uganda. 



The following table summarises these results : — 





Plana 



li O. 



of flies 



•fori 



led. 



AT C A 

 JNO. 01 UcLYS 



before infection 

 took place. 



jivesuir. 



irercentage 

 or 



infected, flies.* 



52 





91 



— 



— 





214 



Uninliabited Lake- 



2500 



98 



+ 



0 '04 





shore 











571 



)> 



1002 



20 





0 "10 



612 



)) )) 



615 



12 



+ 



0-16 



674 



jj )» 



2315 



29 



+ 



0-04 



758 





630 



30 



+ 



0 -16 



976 



3) )) 



440 



12 



+ 



0-23 



1117 





525 



11 



+ 



0-19 



1276 



J> )J 



300 



13 



+ 



0-33 



1462 





505 



10 



+ 



0-19 



1465 





295 



14 



+ 



0-34 



982 



Jl )) 



456 



16 



+ 



0-22 



* This is calculated on the assumption that tliere is only one infected fly in eacli batch of flies 

 used in an experiment. 



It must therefore he concluded that the Glossina palpalis on the uninhabited 

 shores of Victoria Nyanza can retain their infectivity for a 2)criod of at least 

 two years after the native population has been removed. How much longer 

 they will remain infective it is impossible to say, but it is obvious that 

 these experiments should be continued, in order to answer this important 

 question. 



With the facts at our dis|)osal it is not possible to account for this 

 continued infectivity. It may be due to the duration of the life of these 

 flies being more than two years — that flies which became infected before the 

 natives left are still alive. Or, it is possible that the flies have lately fed on 

 natives, suffering from Sleeping Sickness, who have been passing in canoes 

 from the islands to the mainland, or on natives who still frequent the 

 Lake-shore in spite of the prohibition. Thirdly, it might be explained, if 

 any of our canoe-men or lly-boys had try})anosomes in tlieir blood. Or, 

 lastly, it is possible that the mammals and birds along the Lake-shore have 

 become infected, and so act as a reservoir of the disease. 



To tliese speculations it may be answered that it is not at all likely that 

 these Hies have the opportunity of becoming infected from passing canoes, 

 which during the last two years have been few and far between, or to natives 

 still frequenting the Lake-shore. Our canoe-men and fly-boys have been 

 kept un(l(!r careful supervision (hiring th(> whole of [\w time, their blood 

 coiiHt.'mLly (sxamiiKMl, and oncse a montli blood fiom eacli of them injected 

 into a healthy monkey. There remain, then, the two theories — long duration 



