324 
EASTERN ETHIOPIA 
XXVI 
carefully investigated animals bitten by the tsetse fly 
known as Ulossma morsitans and succeeded in proving 
that 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 suffering from sleeping sickness. Those flies 
which had fed were then confined in cages and allowed 
to bite monkeys, and the bitten monkeys acquired 
sleeping sickness in consequence. It has been estimated 
from careful observation that among wild tsetse Hies, 
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 
but-^-pr^'vimrdy^^drenr^^ men, women, and children, 
black or white. The black 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 than man G. obtains its trypanosomes. 
