xxvi FLIES AND SLEEPING SICKNESS 325 



but also if the trypanosome undergoes any meta- 

 morphosis after it has been acquired by the fly. 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. < i<(i nl dense 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, arid 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. Rats 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 tart rate of antimony will cause a very 

 rapid disappearance of the trypanosomes from the 



