PLAN OF CAMPAIGN 201 



malaria and yellow fever, did the fly act as host ? 

 Did, in other words, the parasite pass part of its life 

 cycle in the fly, as did the malaria parasite in the 

 mosquito ? The answer, as furnished by tlie experi- 

 ments of Kleine and Bruce, point to the con- 

 clusion that, much as in the case of yellow fever virus 

 in the stegomyia, a latent period exists in the fly 

 during which period it is not infectious, but tliat 

 after the period of latency, the fly becomes again 

 infectious. In the case of the Sleeping Sickness 

 parasites the latent period appears to be from 14 to 

 21 days. These observations point to the fact that 

 the fly acts as a true host to the trypanosome just 

 as the anophelines do to the parasite of malaria ; in 

 other words, the fly appears necessary to the propa- 

 gation of the disease. 



Plan of Ccnnpaign. — Having proved that the tsetse 

 fly is the carrier of sleeping sickness, and proved more- 

 over, as it would appear from the most recent 

 observations, that it is only one species, the Glosslna 

 palpalis, that can act as host to the trypanosome, 

 we have the key of the plan of preventing the disease 

 altogether, viz. by exterminating the carrier, precisely 

 as in the plan of campaign against malaria, yellow 

 fever, and plague. 



The tsetse fly, like the common house fly and 

 like the mosquito, has its two phases — the adult winged 

 form and the larval form. It can be attacked at both 

 stages, whichever is most practical or most convenient. 



In the first place, observations have shown that 

 the breeding place of the fly is the strip of ground 



