XXVI 
FLIES AND SLEEPING SICKNESS 
325 
but also if tlie trypanosome undergoes any meta¬ 
morphosis after it has been acquired by the hy. This 
has involved a large amount of investigation, and much 
more work is required before these questions can be 
satisfactorily answered, but we now know that the tsetse 
fly is something more than a mere transmitter of 
trypanosomes. 
In the latest reports of the Sleeping Sickness 
Commission sent out in 1908, it is stated the trypano¬ 
some T. gambiense does multiply in the gut of the fly. 
The flies become infective on an average thirty-four 
days after their first feed on infective blood, and it was 
proved that a fly may remain infective for seventy-five 
days. 
These conclusions are very important, because, with 
the idea of preventing the spread of the disease, the 
natives were removed from the islands in the Victoria 
Nyanza and isolated from the flies. Two years after 
these evictions the flies along the shores of the 
depopulated islands were examined and found to be 
infective. Experiments were made to find out if the 
birds and large mammals, such as the hippopotamuses 
on the lake shore, were capable of giving sleeping 
sickness to man by means of the fly, but the results 
were negative. 
It is an important feature in sleeping sickness that 
the disease can be experimentally produced in other 
animals than man. Eats are susceptible. This enables 
experiments to be performed to test the value of drugs. 
In the treatment of the disease Thomas discovered that a 
remedy known as atoxyl caused the disappearance of 
the parasites, but further observations showed that 
after a time they reappeared in the blood. The experi¬ 
menters then realised the astonishing fact that the new 
swarm was not affected by the drug, they had become 
atoxyl-proof. Plimmer has proved that the hypodermic 
use of sodium tartrate of antimony will cause a very 
rapid disappearance of the trypanosomes from the 
