324 EASTERN ETHIOPIA xxvi 



carefully investigated animals })itteii by the tsetse fly 

 known as (Jlossina nioisitan.'^ and succeeded in jiroving 

 tliat the fly-disease (Nagana) in horses, cattle, and dogs 

 was due to the presence in the blood of a trypanosome, 

 and that this fly could convey the disease from an 

 infected to a susceptible animal. 



As soon as the nature of sleeping sickness was 

 appreciated, its analogy to nagana led the investigators 

 to suspect a biting insect as the conveyer of the parasite. 

 Steps were taken to ascertain the distribution of the 

 sleeping sickness, in order to determine if it coincided 

 with that of any known biting insect, for the tsetse fly 

 was at once suspected. The results of this investigation 

 were very conclusive, for these flies swarm on the 

 shores and islands of the Victoria Nyanza, and 

 especially in places where the half-naked natives meet 

 in thousands to trade in fish, bananas, etc. 



Experiments were then conducted with tsetse flies. 

 The insects, enclosed in cages, were allowed to feed on 

 natives suftering from sleeping sickness. Those flies 

 which had fed were then confined in cao;es and allowed 

 to l)ite monkeys, and the bitten monkeys acc[uired 

 sleeping sickness in consequence. It has been estimated 

 from careful oljservation that among wild tsetse flies, 

 1 in 400 is infective. (Bruce.) 



The large amount of careful experimental work has 

 satisfactorily settled the question that the parasites, 

 which cause sleeping sickness in man, can be conveyed 

 from patients affected with trypanosomiasis to suscep- 

 but previously healthy men, women, and children, 

 black or white. The l^lack people are more easily in- 

 fected than the white, for the latter wear clothes. In 

 the districts where this disease exists it is no uncommon 

 thing to see partially clothed natives sitting in the sun 

 and their bronze-like bodies dotted with flies. 



From a prophylactic point of veiw it becomes 

 important to determine not only from which animals 

 other tluin man (/. p'llp'i^i^ ol)tains its trypanosomes. 



