112 INFECTIOUS AND PARASITIC DISEASES. 



man by one of their hosts which itself is also a human 

 parasite. An instance of the latter is found in the 

 malarial plasmodium, which is inoculated by the 

 anopheles mosquito. 



The principal human protozoan parasites are the 

 amoeba dysenterice, the trypanosoma gambiense, the pro- 

 tozoan of Dum-Dum fever, and the Plasmodium ma- 

 laricB (three varieties). 



This parasite is the cause of an acute and 

 Amceba chronic dysentery principally 



Dysenteric., prevalent in Egypt, India, 

 and tropical countries gen- 

 erally, although it also occasions a large 

 proportion of the cases of dysentery in 

 the United States. 



The site of its activity is the large intes- co^Gr'^^^t^er 

 tine, the mucous membrane of which it Braun.) 

 erodes and undermines to an extent seen in no other 

 malady. The organism gains entrance into the body 

 in the drinking-water and through polluted vegetables 

 which are eaten raw. There is a special tendency to 

 abscess of the liver in dysentery of amoebic origin, and 

 perforation of the abscess through the diaphragm into 

 the right lung is a not uncommon event. In appear- 

 ance this amoeba is not unlike the white corpuscles of 

 the blood. Harmless amoebae, however, also occur 

 normally in the stools and must be differentiated from 

 the pathogenic amoeba histolytica. 



