336 DR. W. YORKE ON 



large numbers of European officials and others, it was not until 

 towards the end of 1909 that the first white case was discovered. 

 Since then, although the Luangwa Yalley has been closed, quite 

 a number of Europeans have contracted the disease in North- 

 Eastern Rhodesia. Moreover, we must remember that some time 

 before 1909 scientific experts had travelled through the Luangwa 

 "Valley without discovering a single case either native or 

 European. 



The hypothesis that human beings can harbouL l j ^jarasite 

 for long periods of time, as do the wild fauna, without exhibiting 

 signs of disease, is one which I cannot support. Amongst the 

 cases discovered by us, several piesented practically no symptoms, 

 the only indication of the disease being the presence of tiypano- 

 somes in the blood ; yet without exception they were all dead 

 within six months. 



Professor Minchin suggests that if the game in a "fly" area 

 were destroyed, the "fly "would enter the villages and attack 

 human beings and the cattle surrounding their habitations. 

 To this objection I have already referied in my paper. Cattle 

 are not as a rule fovxnd in A'illages situated in " fly " districts, and 

 the " fly " does not invade villages around which there is a 

 clearing, even though at the present time they could by so doing 

 obtain food still more readily than they do in the bush. 



Regarding the letter of the Hon. Walter Rothschild, I have 

 already in my paper discussed the suggestion that after the 

 extermination of the game the fly would be driven to attack 

 monkeys, rats, and mice. Even if this occurred, these animals 

 quickly succumb from trypanosomiasis, and therefore cannot 

 have the same significance as reservoirs of the disease as the big 

 game which are tolerant of the parasites. 



With regard to the first objection raised by Sir Henry Seton- 

 Karr, I must ask what are the other reservoirs of the virus ; 

 and if there be any, is that a reason why the main reservoir 

 should not be destroyed ? Passing to the second point, I submit 

 that the connection between big game and sleeping sickness has 

 been fully and amply established.. As to the thii'd point, 

 the greater freedom of intercoui^se among native tribes under 

 white protection has undoubtedly played a part in the spread of 

 the disease. But if civilisation and progress is to continue, this 

 freedom of intercourse must also continue, and the population 

 will of necessity run more risk of infection than previously. 

 Recognition of this fact makes it all the moi-e essential that we 

 should endeavour to render the " fly " as non-infective as possible 

 by destroying the reservoir of the virus. As the last point is 

 fully discussed in my paper, I need not refer to it again. 



In reply to Sir Alfred Sharpe, I must point out that we have 

 established beyond all doubt that Glossma morsitans does transmit 

 sleeping sickness under natuiul conditions. I cannot see how 

 further knowledge as to whether there are other distributing- 

 agents affects the question, beyond the fact that if this be proved 



