Tsetse-flies and Sleeping Sickness of Man 217 



well as for Trypanosoma brucei the fly served as an essential host. 

 Indeed, Kleine and many subsequent investigators are inclined to 

 think that there is practically no mechanical transmission of trypan- 

 osomes from animal to animal by Glossina in nature, and that the 

 many successful experiments of the earlier investigators were due 

 to the fact that they used wild flies which already harbored the 

 transformed parasite rather than directly inoculated it from the 

 blood of the diseased experimental animals. While the criticism 

 is applicable to some of the work, this extreme view is not fully 

 justified by the evidence at hand. 



Kleine states (19 12) that Glossina palpalis can no longer be 

 regarded as the sole transmitter of sleeping sickness. Taute (191 1) 

 had shown that under experimental conditions Glossina morsitans 

 was capable of transferring the disease and Kleine calls attention to 

 the fact that in German East Africa, in the district of the Rovuma 

 River, at least a dozen cases of the disease have occurred recently, 

 though only Glossina morsitans exists in the district. It appears, 

 however, that these cases are due to a different parasite, Trypano- 

 soma rhodesiense. This species, found especially in north-east 

 Rhodesia and in Nyassaland, is transferred by Glossina morsitans. 



Other workers maintain that the disease may be transmitted by 

 various blood-sucking flies, or even bugs and lice which attack man. 

 Fullebom and Mayer (1907) have shown by conclusive experi- 

 ments that Aedes {Stegomyia) calopus may transmit it from one 

 animal to another if the two bites immediately succeed each other. 



It is not possible that insects other than the tsetse-flies (and only 

 certain species of these), play an important r61e in the transmission 

 of the disease, else it would be much more wide-spread. Sambon 

 (1908) pointed out that the hypothesis that is spread by Aedes 

 calopus is opposed by the fact that the disease never spread in the 

 Antilles, though frequently imported there by West African slaves. 

 The same observation would apply also to conditions in our own 

 Southern States in the early part of the past century. 



Since Glossina palpalis acts as an essential host of the parasite 

 and the chief, if not the only, transmitter, the fight against sleeping 

 sickness, like that against malaria and yellow fever, becomes pri- 

 marily a problem in economic entomology. The minutest detail 

 of the life-history, biology, and habits of the fly, and of its parasites 

 and other natural enemies becomes of importance in attempts to 

 eradicate the disease. Here we can consider only the general features 

 of the subject. 



