HOST-PARASITE RELATIONS: INTESTINAL PROTOZOA 



when once infected may remain infected throughout the 

 rest of his life. He may never show symptoms, but is 

 always liable to come down with an acute infection. 

 If an acute infection appears he may recover with or 

 without treatment. Such a recovery, however, is often 

 followed by one or more relapses as in many other pro- 

 tozoan diseases. Just what modifications in the host or 

 parasite are responsible for relapses are not known with 

 certainty. 



II. HOST-PARASITE SPECIFICITY 



No comprehensive study has yet been made of the 

 host-parasite specificity of E. histolytica. Spontaneous 

 infections with this species have been reported in certain 

 species of lower animals and experimental infections 

 have been obtained in primates, carnivores and rodents. 



Primates. Both spontaneous amoebic dysentery and 

 amoebic liver abscess have been reported in monkeys, 

 and Suldey (1924) has recently noted acute dysentery 

 in a 3-year-old chimpanzee. Many investigators have de- 

 scribed amoebae from primates other than man among 

 which are types resembling E. histolytica and E. coli 

 so closely that they cannot be separated by means of 

 morphological or cultural characteristics. This fact 

 throws doubt on all data obtained as a result of attempts 

 to infect these animals with E. histolytica. Of particular 

 interest is the recent observation of Dobell (1926b) that 

 histolytica-like amoebae from the monkey when cultivated 

 in artificial media and injected into cats produces dysen- 

 tery that differs from that similarly obtained by injec- 

 tions of E. histolytica, thus indicating a physiological 



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