THE PROTOZOA 



197 



ing in swamps with the use of oil, by draining the swamps, or by 

 the introduction of fish whicli cat the mosquito larvai has Ijcen 

 proved from our experiences along the Panama Canal, in the 

 Philippines, in Cuba, and in New Orleans. 



Many other diseases of man are probably caused by parasitic 

 protozoans. Dysentery of one Idnd appears to be cau.sed by the 

 presence of an amcebalike animal in the digestive tract. Small- 

 pox, rabies, and possibly other diseases 

 may be caused b\' the action of these 

 little animals. 



Another group of protozoan parasites 

 are called trypanosonies. One of this 

 family lives in the blood of native 

 African zebras and antelopes ; seem- 

 ingly it does them no harm. But if 

 one of these parasites is transferred 

 by the dreaded tsetse fly to one of the 

 domesticated horses or cattle of the 

 colonist of that region, death of the 

 animal results. 



Another fly carries a specimen of 

 trypanosome to the natives of Central 

 Africa, which causes "the dreaded and 

 incurable sleeping sickness." This 

 disease carries off more than fifty 

 thousand natives yearly, and many 

 Europeans have succumbed to it. Its 

 ra^'ages are now largely confinetl to an area near the large 

 Central African lakes and the Upper Nile, for the fly which 

 carries the disease flies near water, seldom going more than 

 150 feet from the banks of streams or lakes. The British 

 government is now trying to control the disease in Uganda, by 

 moving all the villages at least two miles from the lakes and 

 rivers. Why? In this country many fatal diseases of cattle, 

 as "tick," or Texas fever, among cattle are probably caused 

 by protozoans. 



Skeleton Building. — Some of the Protozoa build elaborate skeletons. 

 These may be formed outside of the body, being oomjjosod of tiny micro- 



How to tell the common mos- 

 quito (culex), u, from the 

 malarial mosquito (anopheles), 

 b, when at rest. Note the 

 position of body and legs. 



