SLEEPING SICKNESS. 335 



supposition that tsetse depends solely on game for its existence. 

 There are striking instances in Nyasaland and Rhodesia of game- 

 less districts full of fly, and flyless districts full of game. 



"3. Referring to the third heading — how would it be possible, 

 to annihilate game ? It must be remembered that it is not only 

 what is known as ' big game' that fly feeds on, but all game, big 

 and small, and almost every form of life in the bush. It would 

 be necessary to annihilate practically every form of life and to 

 remove also every native. This would obviously be impossible. 



" In any case it would be a terrible mistake, which could never 

 afterwards be remedied, to countenance anything in the shape of 

 an attempt to annihilate game in any part of Africa, unless we 

 are absolutely certain beforehand that such a course would not only 

 ensure the extinction of all varieties of tsetse fly, but make sure 

 that all forms of Sleej)ing Sickness would disappear. At present 

 the grounds for such an assumption are totally inadequate."' 



Reply by Dr. W. YORKE. 



As it is impossible in the limited time at my disposal to reply 

 in full to the volume of criticism which my paper has evoked, 

 I must content myself with dealing with a few of the more 

 important and useful points which have been raised. 



Mr. Marshall points out that in giving the percentages of 

 infected game I grouped together all the trypanosomes pathogenic 

 to man and domestic stock, and that this might lead to mis- 

 conception. In our published papers Dr. Kinghorn and I have 

 separated the parasites one from the other, and full particulars are 

 given as to number of each antelope infected with each of the 

 various pathogenic trypanosomes. I might state here that at 

 Nawalia in the Luangwa Valley 16 per cent., and at ISTgoa on the 

 Congo-Zambesi watershed 3*3 per cent., of the wild animals were 

 infected with Trypanosortia rhoclesiense. The statement that in my 

 published papers I have throughout assumed the disease to be a 

 new one in these countries, and not even contemplated the other 

 alternative, is incorrect. Whether the disease be new or old 

 appears to me to be only of secondary importance. What is of 

 the first importance, however, is whether or not the disease is 

 spreading — whether more cases are occurring now than, say, eight 

 or ten years ago. I admit that from the statistics available the 

 question is difficult to answer ; but what evidence there is suggests 

 strongl}^ that during the past few years sleeping sickness has laeen 

 on the increase. Obviously the most reliable information is to 

 be obtained from an examination of the incidence of the disease 

 in Europeans. I cannot think it likely that even anterior to 1909 

 many white people could have succumbed from trypanosomiasis 

 without the disease having been recognised ; yet in spite of the 

 fact that the main roads to the Congo-Zambesi watershed crossed 

 the Luangwa Valley, and that these roads were traversed by 



