226 DISEASES FROM HARMFUL ORGANISMS 



tioning hinders the normal transportation of oxygen by 

 the blood. Moreover, the poisons produced by the 

 malarial parasite bring about definite symptoms of which 

 chills and fever (Fig. 59) are the most familiar. The 

 drug quinine, found in the bark of the cinchona tree, 

 destroys malarial organisms, so that if quinine can be 

 introduced at the time when the organisms are active in 

 the blood, the body can be freed from infection. 



Fig. 5S. — The Pro- 

 tozoan That Causes 

 Malaria. 



Fig. 59. — Successive Stages in the Life 

 History of the Malaria Orj^anism. The period 

 of hi^h fever is during the transition from 

 stage 3 to stage 4. 



There are several species of amoeba (Fig. 60) that live 

 in the human alimentary tract and by means of the 

 poisons which they produce bring about a form of dysen- 

 tery known as tropical or amccbic dysentery. This 



Fig. 60. — An Amccba from the Human Digestive Tract. 



disease occurs chiefly in the tropics and is found in 

 temperate regions only in persons who have come from 

 tropical climates. 



Disease due to Metazoa. — There are various highly 

 organized parasites which may cause disease. Among 

 them is the hookworm, an organism which has attracted 



