HUMAN TRYPANOSOMIASIS 147 



extermination of that reptile. Protection from the bites 

 of flies is very difficult, not only must fly-proof houses 

 be made, but fly-proof clothing must be worn when out- 

 side such houses. Such measures should be taken when 

 living in an endemic area close to native settlements 

 where sleeping sickness is prevalent. 



Biting flies belonging to other families are not to be 

 altogether ignored, as the trypanosomes of Asia are 

 carried by some of these, such as Stomoxys. Attention in 

 Africa has been almost entirely directed to Glossinae. 



Experimentally Glossinae convey trypanosomiasis in 

 two ways. There is direct evidence that occasionally they 

 convey the parasites by feeding first on an infected animal 

 and very shortly afterwards feeding on another susceptible 

 animal. Such transmission is direct. Usually attempts 

 at transmission in this manner fail, but possibly this 

 mode of spread of the disease from man to man does 

 take place at times. Kleine has shown that flies again 

 become infective eighteen days and more after they have 

 fed on infected animals, and remain infective for an 

 indefinite time. 



Attempts to demonstrate a definite cycle of develop- 

 ment of trypanosomes in the Glossinae are difficult 

 because flagellates are so common in the alimentary canal 

 of flies. Bruce and others have shown that laboratory- 

 bred flies do not harbour intestinal flagellates. If such 

 flies be fed on a person or animal with trypanosomes 

 changes occur. In many of the flies the trypanosomes 

 disappear. In a minority the trypanosomes multiply in 

 the intestine, but are long and narrow, or short and 

 stumpy, and not like the forms found in the blood. In 

 these, about the twenty-eighth day (according to Bruce 

 the commonest time for the flies to become infective), 

 trypanosomes are found in the salivary glands, and these 

 trypanosomes are similar in appearance to those found in 

 the human blood. 



In mammals they multiply asexually by longitudinal 

 division (fig. 44). Small resting forms, according to 



