THE SLEEPING SICKNESS 169 



collect flies throughout the country forming a belt 

 of twenty or thirty miles around the north of the lake. 

 Many thousands of flies were thus brought in, and the 

 localities from which they came carefully noted. Among 

 these flies Colonel Bruce recognised a tsetze fly ; and 

 when these collections were received at the Natural 

 History Museum in London, it was at once determined 

 by Mr. Austen, the assistant in charge of our collections 

 of Diptera (or two-winged flies), that the Uganda tsetze 

 fly was not the same species as that of Zululand and the 

 fly country, but a distinct species previously known only 

 on the West Coast and the Congo basin, and described by 

 the name Glossina palpalis. The story thus developed 

 itself: the trypanosome of sleeping sickness is probably 

 carried by this West Coast tsetze fly just as the trypano- 

 some of nagana is carried in the south-east of Africa by 

 the Glossina morsitans and pallidipes, the regular and 

 original " tsetze " flies. 



Sleeping sickness thus presented itself as a special 

 kind of human tsetze-fly disease. To test this hypothesis, 

 Colonel Bruce pursued two very important and distinct 

 lines of enquiry. In the first place he found that those 

 places on his map which were marked as " sleeping-sick- 

 ness areas " were precisely those places from which the 

 collected flies included specimens of tsetze fly, whilst he 

 found that there were no tsetze flies in the collections of 

 flies brought in by the natives from the regions where 

 there was no sleeping sickness. 



His second test inquiry consisted in ascertaining 

 whether the tsetze flies of Uganda are actually found, 

 experimentally, to be capable of carrying the trypanosome 

 from one infected person to another. For this purpose 

 it was necessary to make use of monkeys, certain species 

 of which were ascertained to be liable to the infection of 



