HOST-PARASITE RELATIONS! INTESTINAL PROTOZOA 



ings and has added facts obtained by himself from ex- 

 periments on kittens. Brumpt found specimens of E. coli 

 in small ulcerations in the intestinal mucosa of a kitten 

 that had been given a rectal injection of material con- 

 taining both E. coli and E. dispar, the latter being the 

 name given by him for what he believes to be a species 

 resembling E. histolytica morphologically but differing 

 from it in being non-pathogenic. If this work and the 

 observations of Lynch are confirmed, it must be admitted 

 that E. coli may under certain conditions eat red blood 

 cells and invade the tissues of the intestine. 



Host-parasite specificity. That E. coli finds the human 

 intestine a favorable habitat is evident from the high 

 incidence of infection; about 50 per cent of the general 

 population are carriers of this species. The ease with 

 which infection takes place is indicated by the results 

 of the experiments reported by Walker and Sellards 

 (1913). Twenty men were fed cysts obtained from 5 

 different hosts; 17 of them became infected, cysts being 

 passed in from i to 11 days. No symptoms were ob- 

 served in any of the infected men. Why E. coli should 

 be more successful than E. histolytica is difficult to un- 

 derstand; the latter is parasitic in only about one-fifth 

 as many persons (10 per cent) as is E. coli (50 per 

 cent). 



Many attempts have been made to infect lower animals 

 with E. coli but only recently have any of them been 

 successful. Kessel (1923) reported positive results with 

 rats and later (Kessel, 1924) with monkeys. There is 

 some doubt about the latter since monkeys are apparently 

 naturally infected wi-th an amoeba indistinguishable from 



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