224: ENTOMOLOGICAL OBSERVATIONS IN UGANDA. 



^' It has been proved that cattle in the fly-area do naturally harbour 

 Tfypano.soma gamhiense. 



" It is therefore possible that the cattle and antelope living in the fly-area 

 may act as a reservoir, and so keep up the infectivity o£ the Glossina palpalis 

 for an indefinite period, but there is no proof up to the present that this 

 actually takes place in nature/' 



Mechanical IWmsmission of Sleeping Sickness. 



Until the beginning of 1909 it was generally supposed that trypanosomiasis 

 was conveyed from one animal to another by a purely mechanical process^ 

 that is to say, that individuals of the protozoon remained adhering to the 

 proboscis of the fly after its feed, and were thus transferred to the next 

 animal bitten. But Dr. Kleine's observations, at the end of 1908, showed 

 that in some cases at least tlie parasite undergoes some process of develop- 

 ment in the fly before it can infect a fresh animal. Nevertheless it was still 

 usually held that mechanical transmission was the commoner method of 

 infection. The experiments of the authors were directed to ascertain the 

 validity of this assumption. 



The method adopted was to place a cage of flies upon an infected animal, 

 and while they were feeding to transfer it suddenly to a healthy animal, and 

 backwards and forwards for 10 to 15 minutes. The animals used in these 

 interrupted feedings were : monkey, ox, goat and fowl ; and the experiments 

 lasted generally for a week to 12 days each. In five such experiments 

 positive results were obtained twice, the disease being transferred in one case 

 from a monkey to a monkey, in the other from a monkey to a goat. 



On the other hand, ten experiments were made in which the transference 

 of the flies from the infected to the healthy animal was not instantaneous, the 

 feedings being separated by intervals varj^ing from half an hour to 48 hours. 

 The duration of rach experiment was generally 12 or 13 days, and the 

 number of flies used in each case varied from 7 to 120, with an average of 

 about 50. Only monkeys were used in these experiments, and in every case 

 the results were negative. 



The general conclusions arrived at by the authors are : — 



" 1. The mechanical transmission of Sleeping Sickness by means of 

 Glossina palpalis can take place if the transference of the flies from the 

 infected to the healthy animal is instantaneous — that is, by interrupted 

 feeding. 



" 2. This mechanical transmission does not take place if an interval of time 

 comes between the feedings. 



" 3. Mechanical transmission plays a much smaller part, if any, in the spread 

 of Sleeping Sickness than has been supposed." 



