422 



Infectivity of Glossina morsitans in Nyasaland. 



By Surgeon- G-eneral Sir David Bruce, C.B., F.R.S., A.M.S. ; Majors David 

 Harvey and A. E. Hamerton, D.S.O., B.A.M.C. ; and Lady Bruce, 

 K.E.C. 



(Scientific Commission of the Koyal Society, Nyasaland, 1912.) 

 (Eeceived February 24 — Eead April 10, 1913.) 



Introduction. 



The object of this paper is to put on record the proportion of tsetse flies 

 found in this district of Nyasaland to be infected with disease-producing 

 trypanosomes, and, further, to identify the species of trypanosomes with 

 which the flies are infected. 



It must be understood that this paper only deals with the district lying 

 near the camp at Kasu and not to every part of Nyasaland. The geographical 

 position and other features of this district have already been described in 

 a previous paper.* It is known as the " Sleeping Sickness Area " or 

 " Proclaimed Area," and in it almost all the cases of the Human Trypano- 

 some Disease of Nyasaland have occurred. This disease is caused by 

 Trypanosoma rhodesiense, and the natives give it the name of " Kaodzera," 

 but there is a good deal of evidence accumulating that T. rhodesiense is in 

 reality T. brucei, in which case the disease would be known as " Nagana." 



Definitions. 



In this paper an infective fly is one which contains trypanosomes which 

 have reached the final stage of their development and are capable of giving 

 rise to disease. An infected fly is one in which the development of the 

 trypanosomes may not have reached this final stage, and where, therefore, it 

 may not as yet be disease-producing. An infective fly must be infected, 

 whereas an infected fly need not be infective. 



" Fly " means the tsetse fly, and in this paper the species dealt with is 

 Glossina morsitans. 



Methods Employed. 



The method employed in studying the -infectivity of the flies was simple. 

 Native boys were employed in catching the flies, which were brought up to 

 Kasu in small cages by a native cyclist. Each cage of flies was fed on three 

 healthy animals — the first day on a monkey, the second on a dog, and the 



* Supra, p. 269. 



