HOST-PARASITE RELATIONS I INTESTINAL PROTOZOA 



both rats and mice were chronic instead of acute as in 

 kittens. The experiments of Wagener and Thomson 

 were performed with motile amoebae injected into the rec- 

 tum of amoeba-free rats. Negative results were obtained 

 with 1 6 rats when thus treated and with 4 rats into the 

 cecum of which motile amoebae were injected by laparot- 

 omy. Chiang extended Kessel's work and not only suc- 

 ceeded in infecting rats but in obtaining dysenteric 

 symptoms in cats fed on cysts passed by the rats. He also 

 found that clean rats became parasitized when placed in 

 the same cage with infected rats. Several species of 

 amoebae have been described as normal inhabitants of 

 the rat's intestine; hence there is always danger of con- 

 fusion between these and introduced species. Rat experi- 

 ments must therefore be carried on with extreme care 

 and great familiarity with both the normal and foreign 

 amoebae is necessary to insure reliable data. The evidence 

 indicates that rats and mice may become infected with 

 E. histolytica, but that they are often parasitized by this 

 species in nature, or play anything but a very minor role 

 in transmission is doubtful. 



Guinea-pigs. Of the many investigators who have at- 

 tempted to infect guinea-pigs with E. histolytica only 

 Baetjer and Sellards (1914) and Chatton (1917a, 1918) 

 have reported positive results. Chatton first obtained in- 

 fections by feeding cysts to guinea-pigs and then infected 

 other pigs by the rectal injection of trophozoites from 

 these. No dysenteric symptoms were noted although sev- 

 eral of the experimental animals died, one in 20 days and 

 another in 9 days. The site of infection was the cecum 

 where a hyperplasia of the epithelium of the glands of 



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