1912.] Reservoir for Trypanosoma gambiense. 



311 



in the laboratory. It is, of course, possible that the trypanosomes may be 

 slowly dying out in the buck, and that a greater or less immunity may be 

 left behind. But even if this be so, an animal which can remain infective for 

 22 months may be looked upon as a true reservoir for the virus of sleeping- 

 sickness. It has only to remain in the neighbourhood of the fly to perpetuate 

 the disease indefinitely among susceptible Lake-shore animals. 



The behaviour of the positive flies obtained from Antelope 2371 and 2357, 

 13 and 15 months respectively after the original infection, is interesting. In 

 the first case, the positive fly did not infect the monkey until the 50th day of 

 the experiment ; and in the second instance, a 41-day fly showed no flagellates 

 in either proventriculus or salivary glands. In all previous experiments with 

 these antelope the flies became infective about the 30th day of the 

 experiment. 



An explanation of this curiously slow development of the flagellates in the 

 fly may be that the trypanosomes are present in very small numbers in the 

 peripheral blood of the buck. A fly would then obtain an extremely small 

 number of trypanosomes at a feed, whereas formerly a considerable number 

 may have been imbibed. 



Some support is lent to this suggestion by the prolonged incubation period 

 in Experiment 199 (Eeedbuck 2359), where 18 days elapsed before 

 T. gambiense appeared in the monkey's blood. 



Conclusions. 



1. That the antelope may remain capable of infecting G. palpalis with 

 T. gambiense for a period of at least 22 months after their original infection 

 with this trypanosome. 



2. That there is some evidence to show that an antelope which lias ceased 

 to be infective for T. gambiense acquires some degree of immunity against 

 re-infection. 



