518 Col. D. Brace on Slee^Aiifj Sitkutas in V<janda. [April 22, 



The best animal to carry out these experiments on, of course, is 

 the monkey. The method used is simply to feed tsetse flies on a 

 sleeping sickness case, and, at varying intervals of time, to place the 

 same cage of flies on a monkey. The sleeping sickness patients do 

 not seem to feel the bites of the flies, as they make no complaints 

 or other signs of inconvenience. It is convenient to have, as a rule, 

 about 30 flies in each cage, but only those which fill themselves are 

 to be reckoned as having fed. 



As the result of many experiments, several of which were thrown 

 on the screen, it was shown that the tsetse fly is capable of conveying 

 the virus of sleeping sickness from the sick natives to healthy mon- 

 keys. These feeding exjDeriments were made at various intervals of 

 time, and it was found that the tsetse fly can still give rise to the 

 disease at the end of 48 hours, but not longer. That is to say, a fly 

 which has fed on a sleeping sickness case, and then kept in a cage 

 without further feeding for 48 hours, is thus capable of transmitting 

 the disease to a healthy monkey, but if kept for three days is no 

 longer capable. 



This proves that this tsetse fly can convey the infection from 

 the sick to the healthy. But as 28 per cent, of the natives of the 

 sleeping sickness area have this trypanosome in their blood, doubt- 

 less the tsetse flies caught in this area, which feed on these natives, 

 will be able to convey the disease to a healthy animal without any 

 artificial feeding. 



A further set of experiments was therefore made to show that the 

 tsetse flies caught on the lake shore were already infective, from 

 having fed on the natives liviug along the shore. Cages full 

 of the freshly caught flies were straightway placed on healthy 

 monkeys, and after some days the examination of these monkeys 

 showed that they had become infected with sleeping sickness. 



This then concludes the story of sleeping sickness in Uganda. 

 We have seen that probably this disease was introduced from the 

 Congo on account of the greater movement of natives under the 

 march of civilisation and the Pax Britannica. We have seen that 

 the disease is caused by the entrance into the blood of a protozoal 

 parasite, and that the infection is carried from the sick to the healthy 

 by a species of tsetse fly. We have seen that the distribution of this 

 fly corresponds with the distribution of the disease. Where there is 

 no fly there is no sleeping sickness. In other words, we are dealing 

 with a human tsetse fly disease. 



[D.B.] 



