PARASITIC PROTOZOA 



353 



been more carefully studied than any other disease. It 

 has spread rapidly over a large part of Africa, killing hundreds 

 of thousands of the natives of these regions. The early symp- 

 toms of the disease are various, but infection is usually soon 

 followed by fevers, and the patient gradually becomes anemic 

 and physically and intellectually feeble, with an increasing 

 tendency to sleep. As the stupor deepens the patient loses 

 all desire or power of exertion and soon succumbs to the 

 uncanny death. 



Other animals beside man may be infected with this parasite, 

 but it does not seem to injure them. The parasite is carried 



FIG. 149. Tsetse-fly. (After Hanson; two and one-fourth times natural 



size.) 



from one host to another by a species of tsetse-fly, Glossina 

 palpalis, which resembles somewhat our common stable-fly. 

 It is now known that another tsetse-fly, G. mor si-tans, is 

 also an agent in the transmission of this disease. When the 

 fly sucks blood from an infected animal some of the trypano- 

 somes are taken into its body where they undergo certain 

 changes, the fly usually not becoming infective until about 

 three or four weeks later. It is then capable for a period of 



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