306 SLEEPING SICKNESS [CH. 



next shewn that if large numbers of the wild tsetse-flies in the 

 neighbourhood of Entebbe were caught and fed on healthy 

 monkeys the latter became infected with sleeping sickness. 



The disco^'ery that the tsetse-fly is the carrier of the disease 

 explained why sleeping sickness had not spread in the West 

 Indies in spite of the frequent importations of infected negroes. 

 In the absence of its invertebrate host the disease could not be 

 transmitted from the patients to other persons. 



In 1909, Kleine discovered the very important fact that 

 T. gambiense undergoes a cyclical development in the body of 

 Glossina palpalis, and that once infected the tsetse-fly may 

 remain infective for a considerable period of time. In 1911, 

 Taute, whilst experimenting on the shore of Lake Tanganyika, 

 shewed that G. moysitans was also capable of acting as the 

 invertebrate host for T. gambiense, and that the trypanosome 

 underwent a cycle of development wdthin the body of the insect 

 resembling that in G. palpalis. Finally, Bruce, Hamerton and 

 Bateman, in 1911, shewed that the wild game served as a 

 reservoir for sleeping sickness, as antelopes and reed-bucks 

 could remain infected, and infective, for long periods without 

 presenting any signs of disease. The importance of this 

 discovery from a prophylactic point of view cannot be over- 

 estimated. 



Distribution. At the present time sleeping sickness extends 

 along the west coast of Africa from St Louis in the Senegal, 

 to Benguella in the province of Angola, and inland as far East 

 as the Omo River (Brumpt) and the Victoria Nyanza. The 

 main centres of the disease are the Congo Free State, French 

 Congo, Cameroons, Angola, Senegal and Senegambia, Uganda 

 and along the shores of Lake Victoria and Tanganyika. 



Life history within the vertebrate host — Endogenous cycle. — 

 The life-cycle of T. gambiense has been elucidated by the 

 researches of Minchin, Roubaud, Bruce, Kleine, and Miss 

 Robertson. The last named investigator has given a complete 

 description of all stages in the development, from which the 

 following account is taken. 

 ^ In the blood the short forms (so-called female forms) about 

 13 to 20 microns in length (Fig. 75) are the adult type. They 



