TRYPANOSOMES 



375 



in other organs of the body. They have been found in many 

 mammals, birds, frogs, and insects. Some of these scarcely de- 

 serve the name parasite, since their presence in the digestive 

 tract seems to cause the host no inconvenience. To this class 

 belongs Entamoeba coli, which is found in the human intestine 

 in a large percent, of normal individuals. Entamoeba histoly- 

 tica, however, penetrates the wall of the intestine and causes 

 the disintegration of the tissues, or ulceration. This is the 

 cause of tropical dysentery, a serious and often fatal disease, 

 which is quite common among the people of tropical countries. 

 766. Among the Flagellates the Trypanosomes are the most 

 important group of parasites. They find their hosts among all 



Fig. 239. — A Trypanosome. /, Flagellum; >n, undulating membrane; n, nucleus. 



(From Marshall after Doflein.) 



the classes of Vertebrates, as well as some invertebrates, but 

 the Mammals are most seriously affected. The parasite is 

 usually found in the blood and causes intermittent fever, swelling 

 of the spleen and lymph glands, anaemia, eruptions of the skin 

 and disorders of the nervous system. Trypanosoma gambiense 

 is the cause of the terrible ^'sleeping sickness" of South Africa. 

 It is apparently the toxic effect of the parasite on the nervous 

 system that produces the later symptoms of the disease, a 

 lethargic condition which slowly leads to a continuous sleeping 

 and finally ends in death. In large parts of South Africa the 



