206 ZOOLOGY 



the back, the ends not projecting as they do in ordinary 

 flies. Glossina palpalis is the principal transmitter of 

 sleeping sickness, or rather of the protozoan which 

 causes it. Through the extension of commerce in tropi- 

 cal Africa the disease has been enormously extended, and 

 has destroyed the lives of untold thousands of native 

 people. The sickness is of long duration, and eventually 

 the victims sleep to death. Another tsetse fly, Glossina 

 morsitans, carries the trypanosome of nagana disease, 

 which makes it impossible to keep cattle in some dis- 

 tricts. It is found that the large wild animals of Africa 

 harbor the parasite, without suffering any serious conse- 

 quences ; hence they serve as a reservoir from which the 

 tsetse flies may always renew the supply. At Floris- 

 sant, in Colorado, several species of fossil tsetse flies 

 have been found, and it is surmised that at one time 

 these may have been carriers of the organisms of dis- 

 ease. Today there are no species of Glossina living in 

 the Western Hemisphere. 



Tick fever 8. Other disease-producing Protozoa, belonging to 

 the genus Babesia, are carried by ticks. One of these 

 gives rise to a fatal affection of cattle, in which the red 

 blood corpuscles are broken up. In the Southern states 

 cattle have acquired a tolerance of this parasite, just as 

 in tropical countries the negroes are relatively tolerant 

 of malaria. When such cattle, infested by ticks, are 

 driven northward, the ticks may leave them and bite 

 Northern cattle, which then succumb to the disease. 

 The cause of Rocky Mountain spotted fever, a disease 

 which is very fatal to men in certain districts, is also 

 carried by ticks, but of a different species from those 

 living on cattle. Fortunately the disease is at present 

 rare and local, though the ticks are widespread. 



