70 COLLEGE ZOOLOGY 



6. PATHOGENIC PROTOZOA 



The PROTOZOA that cause diseases are said to be pathogenic. 

 One of the best known of these is the malarial fever parasite, 

 Plasmodium. This species belongs, with many other important 

 parasites, to the class SPOROZOA, but all protozoan parasites do 

 not belong to this class. There are many injurious parasites in 

 each of the other classes, and these affect both man and other 

 animals. The importance of pathogenic PROTOZOA has but re- 

 cently been recognized, and, although a vast amount of work has 

 been done in this field, still comparatively little is known about 

 them. A few examples of those affecting man are described in 

 the following paragraphs. 



Rhizopoda. - - Minute ameba-like organisms, named Enta- 

 meba histolytica, are the cause of amebic dysentery, and are always 

 found in the alimentary canal of patients suffering from this 

 disease. They cause ulcers and other lesions producing enteritis. 

 Other ameboid organisms, which are probably referable to 

 the RHIZOPODA, accompany hydrophobia and may destroy the 

 nerve cells of the brain. In smallpox similar ameboid organisms 

 attack and destroy the epithelial cells of the skin. Whether or 



not these structures are the direct 

 cause of the disease mentioned or 

 are merely accessories is not known, 

 but they are to be looked upon as 

 dangerous until they are proved to 

 be harmless. 



FIG. 44. Trypanosoma gam- Mastigophora. - - The Trypano- 

 biense the parasitic FLAGELLATE SQma j s aj . thg present t i me t h e 

 which causes sleeping sickness. > / 



(From Calkins.) most widely studied of all parasitic 



MASTIGOPHORA that affect man. 



In certain parts of tropical Africa they cause the disease called 

 trypanosomiasis, commonly known as sleeping sickness. Try- 

 panosomes are also parasitic in rats and other animals. The 

 species affecting man is named Trypanosoma gambiense (Fig. 44) . 



