HOST-PARASITE RELATIONS I INTESTINAL PROTOZOA 



or transitory hosts or habitats and facultative or obliga- 

 tory species of protozoa. 



Control. And finally, if we wish to control the proto- 

 zoa either in man or in a free-living habitat, we apply 

 similar methods. For example, when a person has an at- 

 tack of amoebic dysentery due to the presence in his 

 intestine of large numbers of specimens of Endamoeha 

 histolytica he is treated with a therapeutic agent, such as 

 emetin or yatren ; and when a reservoir of water becomes 

 overrun with flagellates of the genus Synura, thus caus- 

 ing obnoxious odors and tastes, it is treated with a dose 

 of copper sulfate. 



Cases could be multiplied almost indefinitely bringing 

 out homologies and analogies between free-living and 

 parasitic protozoa but the data presented are sufficient to 

 prove that the same principles govern both these types 

 of organisms as regards morphology, physiological proc- 

 esses, life-cycles and their relations to their physical and 

 biological environments. The relations between parasitic 

 protozoa and their hosts must, therefore, be studied as 

 biological phenomena just as we are accustomed to study 

 the relations between free-living protozoa and their en- 

 vironment. 



3. THE INTESTINAL PROTOZOA LIVING IN MAN 



Each of the four classes of the protozoa include "in- 

 testinal" species that live in man; these are represented 

 in the accompanying figures and referred to by number 

 below. To the Class Sarcodina belong six species of 

 amoebae, Endamceha gingivalis (Fig. 5) in the mouth, 

 and Endamoeha coli (Figs. 2a, 2b), Endamoeha hist a- 



16 



