TRANSMISSION OF DISEASES BY INSECTS 



263 



FIG. 275. Tsetse fly, Glossina 

 morsitans. X 2. 



jects forward, and is stout, owing to the ensheathing palpi; the base of 

 the labium forms a prominent bulb. These are the more conspicuous 

 characters that serve to distinguish tsetse flies from other blood-sucking 

 flies with which they might be confused. 



The mode of reproduction as described by Brauer is similar to that 

 of the group of parasitic flies known as Pupipara. The fly produces a 

 full-grown larva, which at once creeps to 

 some resting place and forms a black 

 puparium. 



Tsetse flies frequent hot, humid regions, 

 near bodies of water, and are restricted to 

 shaded situations, never occurring on the 

 open plains. Both sexes are bloodthirsty 

 but bite only during the daytime as a rule; 

 though they may bite at night when the 

 moonlight is bright. Travelers take advan- 

 tage of the habits of the fly to journey by 

 night; spending the day in an open unin- 

 fested pla&e. 



Nagana. The colon'zation of South 



Africa was greatly retarded by nagana, a disease invariably fatal to 

 the horse, donkey and dog, and usually fatal to cattle, but not affect- 

 ing man. Livingstone and other explorers in regions where nagana is 

 prevalent record their having been bitten by tsetse flies thousands of 

 times with no result other than a slight irritation. 



Bruce was the first to prove the identity of nagana and tsetse-fly 

 disease and to demonstrate the role of the fly in the transmission of the 

 disease. His investigations, begun in Zululand in 1894, are of funda- 

 mental importance and have given an immense stimulus to the study 

 of trypanosomes. 



After finding that no bacteria were concerned in nagana, Bruce dis- 

 covered trypanosomes in the blood of cattle affected with the disease. 

 He inoculated their blood into healthy horses and dogs and in a few days 

 the blood of these animals was teeming with trypanosomes. Then he 

 took healthy animals from the mountain on which he had located his 

 headquarters down into the "fly country;" there they contracted the 

 tsetse-fly disease and showed in their blood trypanosomes indistinguish- 

 able from those of nagana. 



Horses taken into the fly country but not allowed to eat or drink 

 there, took the disease; furthermore, supplies of grass and water brought 



