HOST-PARASITE RELATIONS: INTESTINAL PROTOZOA 



failed in every case. He appears to have been success- 

 ful, however, in infecting dogs with cat coccidia and 

 cats with oocysts from dogs. One kitten was infected 

 with oocysts of Isospora felis and /. rivolta from dogs, 

 and exhibited intermittent diarrhea, and 4 of 8 dogs were 

 infected with oocysts of /. felis and /. rivolta from cats. 

 Apparently, therefore, these two species are infective 

 to both cats and dogs and represent, so far as we know 

 at present, the only examples of coccidia that are able 

 to live in more than one species of mammal. 



Digestion experiments. Andrews (1927) tested the 

 effects of the environment within the stomach and duo- 

 denum of cats and dogs on oocysts of Eimeria from 

 rabbits and on those of Isospora from cats and dogs. 

 He found that very few of the Eimeria oocysts were 

 affected within 72 hours in the cat and within 24 hours 

 in the dog, but that sporozoites were liberated from 

 Isospora oocysts in the cat within 48 hours and in the 

 dog within 24 hours. Selective digestive action on the 

 oocysts enables the sporozoites of the coccidia natural to 

 the host to escape more quickly than those foreign to 

 the host; the foreign oocysts thus have less chance to 

 bring about an infection since they are passive bodies and 

 are continually being carried further down the intestine. 

 Andrews also attempted to determine whether the mero- 

 zoites of foreign coccidia are able to bring about an in- 

 fection by obtaining specimens of Eimeria perforans 

 from the intestine of the rabbit and injecting them intra- 

 duodenally into dogs and cats. Experiments on 3 dogs 

 and 3 cats were unsuccessful but a control cat into which 

 merozoites of Isospora felis from a cat were injected 



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