INTESTINAL PROTOZOA OF MONKEYS 31 



monkey. Kessel (1928a) reports the successful infection of a 

 domestic pig with E. histolytica of the monkey but no attempt was 

 made to infect monkeys with the E. histoIytica-Vikt amoeba of the 

 pig. Numerous cross-infection experiments and many intricate 

 problems in host-parasite relationships are awaiting solution and 

 it seems logical to assume that monkeys may be used to advantage 

 in investigating the same. 



Hegner (1928^ and 1929) has emphasized the evolutionary sig- 

 nificance of the similarity between the intestinal protozoa of mon- 

 keys and of man. While this phase of the subject is of undoubted 

 significance, the facts must not be overlooked that other domestic 

 and laboratory animals, e.g., the rat and the domestic pig, also 

 harbor intestinal protozoa, some of which exhibit the same close 

 relationships to the intestinal protozoa of man that are exhibited 

 by the intestinal protozoa of monkeys. The similarity of these 

 infections of the rat and the pig to the intestinal protozoa of man 

 would be attributed to close association of man and these animals 

 rather than to close evolutionary relationship, and it appears to the 

 writer that such relations of association as well as similarity in 

 diet between hosts should not be lost sight of in discussing the 

 evolutionary significance of intestinal protozoa. 



