HOST-PARASITE RELATIONS: INTESTINAL PROTOZOA 



prepatent period is surprising; it suggests that some of 

 the specimens noted on the first and second days after 

 ingestion might have been among those fed to the patients 

 and not the offspring of the original specimens that had 

 succeeded in estabHshing themselves in the intestine. 



The patent period. In all cases specimens were passed 

 from the time they first appeared to the termination of 

 the experiments. The duration of the patent period was 

 therefore at least as long as the patients were kept under 

 observation. 



The incubation period. Only 4 of the 18 positives 

 suffered from dysenteric symptoms, the incubation 

 periods being 20, 57, 87, and 95 days in length. The 

 other 14 positives may, however, have exhibited symp- 

 toms after observations ceased. 



The carrier period. Apparently all persons infected 

 with E. histolytica become carriers; those who never 

 exhibit symptoms are ''contact" carriers according to 

 Walker's terminology, and those who pass cysts after 

 suffering from dysentery are "convalescent" carriers. 

 Unless rid of their amoebae by the aid of drugs, carriers 

 remain infected for many years. During this time they 

 are always in danger of a disturbance in the equilibrium 

 between host and parasite which will bring about the 

 appearance of symptoms which, in the case of conva- 

 lescent carriers, would constitute a relapse. 



The incubation period in cats. Infections with E. his- 

 tolytica from man have been obtained by many investiga- 

 tors in kittens. The course of the infection in this host is 

 very different from that in man. The infected cat ex- 

 hibits symptoms, but does not pass cysts and hence does 



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