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DH. W. YORKE OK 



of what, in the light of this kiiowledge, can be done to stamp 

 out Sleeping Sickness or to limit its spread in Nyasaland and 

 Rhodesia. Obviously the most satisfactory means of prevention 

 would be the extermination of Glossina morsiians, which conveys 

 the parasite from one vertebrate host to another. Unfortunately, 

 however, this is out of the question at the present stage of our 

 knowledge. The only known method of getting rid of the fly 

 from a district is by clearing away the bush. In the immediate 

 vicinity of villages such a procedure is doubtless feasible and 

 would be attended by valuable results, and natives should be en- 

 couraged to do everything possible in this direction. The labour 

 involved in clearing large tracts of country would, however, 

 be so great that this can be at once set aside as impi'acticable. 

 Moreover, it must be remembered that not only would the 

 country have to be cleared, but it would require to be kept 

 cleared. Everyone who has had experience of Tropical Africa is 

 familiar with the dense shrub growth which springs up in the 

 site of old garden cleai'ings, two or three years after the natives 

 have ceased cultivating the land. This shrub growth is exceed- 

 ingly favourable to Glossina morsitans, so that unless the country 

 be constantly kept cleared the last state of the district is \^orse 

 than the first. 



At present but little is known of the bionomics of Glossina 

 morsitans. The results of investigations carried out up to the 

 present indicate that this tsetse fly has no particular breeding 

 places, but that its pupse are deposited in a more or less haphazard 

 manner in hollow trees and excavations where they are not likely 

 to be disturbed by game-birds. Regarding the liability of the 

 fly to disease and of its natural enemies we know nothing. Much 

 more information is reqxiired on this subject, but it seems only 

 too obvious that the investigations will be beset by great diffi- 

 culties and that the information will only be forthcoming as the 

 result of much slow and tedious work. In fact, to those familiar 

 with morsitans country the extermination of the fly must seem 

 an almost impossible procedure. 



In Uganda, where the disease is spread by Glossina palpalis, 

 the removal of the population a short distance away from the lake 

 shores and water-courses was followed by most excellent results. 

 Such a measure, however, is impossible in Nyasaland and Rhodesia, 

 where the vector Glossina morsitans is practically ubiquitous in 

 its distribution and not limited to water-courses as is Glossina 

 palpalis. 



In view of the impossibility of exterminating the fly and of the 

 equal impossibility of removing the population from the fly belts, 

 we must consider the only way that remains of combating the 

 disease, that is the advisability of attempting to destroy the 

 reservoir of the virus. It is obvious that the mere isolation of 

 infected human beings is futile in view of the fact that the main 

 reservoir of the virus is the blood of the big game. 



And now we come to a subject to which I particularly wish to 



