HOST-PARASITE RELATIONS: INTESTINAL PROTOZOA 



accepted at their face value since he did not take into 

 account the fact that rats are naturally infected with 

 other species of amoebae. Brug (1919a) noted what were 

 apparently infections with E. histolytica in two wild rats 

 in Java and seems to have been successful in infecting 

 a specimen of Miis rattus. Kartulis (1891) also reported 

 spontaneous infection in rats. The most successful ex- 

 perimental infections in rats and mice are those described 

 by Kessel (1923). Rats were fed human feces contain- 

 ing histolytica cysts ; 8 of 29 specimens became infected. 

 The infection was of the chronic type ; cysts were passed 

 in the feces; and other rats were infected by feeding 

 them these cysts. One of 10 mice was also infected by 

 ingesting histolytica cysts ; this mouse passed cysts in its 

 feces. Rats and mice, according to Kessel's results, not 

 only may become infected and pass cysts, but histolytica 

 cysts may pass through their digestive tract and appear 

 in their feces in a viable condition. The fecal pellets of 

 such animals might bring about the contamination of 

 food or drink and hence infection in any susceptible 

 human host. However, it seems probable that infection 

 is very seldom spread in this way, even if Kessel's results 

 should be confirmed by other investigators. It has been 

 found possible to infect other domestic animals, such as 

 cats and dogs, with E. histolytica (see p. 113). Cysts may 

 pass through the digestive tract of the cat unharmed 

 (Dobell, 1919a) but since infected dogs and cats do not 

 ordinarily pass cysts these animals play a minor role, 

 if any, in the transmission of intestinal amoebse. 



The activity of the host and passivity of the parasite 

 in transmission. An important fact that has been brought 



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