132 INSECTS AND MAN 



present in enormous numbers, was spreading disease far 

 and wide among the cattle, and was soon proved to be also 

 a vector of sleeping sickness. The importance of this dis- 

 covery is apparent, when the habits of the two tsetse flies 

 are taken into consideration. Were the disease carried by 

 Glossina palpalis alone, there might be some hope of its 

 ultimate eradication, or of its being kept well in hand; 

 for palpalis has a limited distribution, and is never found 

 far from water, either river or lake ; in short, it frequents 

 well-marked "fly belts," and excellent results have been 

 attained in Uganda by a wholesale removal of the native 

 population from the watercourses and lake shores, and so 

 out of the " fly belt." Glossina morsitans is not confined 

 to the neighbourhood of water, or even to low-lying ground, 

 being found even at elevations of five thousand feet. It 

 is, however, confined to somewhat arbitrary boundaries or 

 " belts," though why this should be so is curious, for it is 

 absent from many topographically and climatically similar 

 stretches of country. It is the most widely distributed 

 of all the Olossina species, extending from Senegambia 

 to Abyssinia, and as far south as Zululand. So that now 

 whole districts, which only a few years ago were considered 

 unlikely to be visited by this disease, are obviously liable 

 to come under its fatal spell. Indeed, although these two 

 flies are the only two proved carriers of sleeping sickness, 

 all the species of Glossina must be viewed with suspicion. 

 Glossina fusca and Glossina pallidipes have been arti- 

 ficially infected with the trypanosome : time alone can show 

 whether they, or their relatives, transmit it naturally. A 

 word or two concerning the transmission of sleeping sick- 

 ness may not be out of place. When one of the species of 

 Glossina in question bites an infected patient, that is to 

 say, a man harbouring in his blood the trypanosome re- 

 sponsible for sleeping sickness, it is in a position to transmit 

 the disease ; and this may take place in one of two ways, 

 either mechanically or by reason of the fly itself becoming 



