CROSS-INFECTION EXPERIMENTS 103 



made. Kessel (1928a) reports having infected young pigs with 

 E. nana, E. coli, and Chiloniastix, and we generally assume the 

 lodaincvba of the pig and man are identical. However, no actual 

 experimental work has been performed in which the lodanKJcha of 

 man has been experimentally transferred to the pig. The chief 

 difficulty that the writer has experienced thus far has been that he 

 has never been able to find, without doubt, a young animal which 

 has been free from a natural lodanwcba infection. Apart from 

 Smith's (1910) observation of an amoeba in the tissue none of 

 the other common intestinal protozoa have been found to produce 

 lesions in the pig. 



The writer hoped that the pig might be found to be a suitable 

 animal for protozoiasis studies, but it appears, for the most part, 

 at least, that the pig serves merely as a temporary reservoir host 

 without exhibiting pathological symptoms. Further, on account of 

 their size pigs are not animals to be kept easily under laboratory 

 conditions. The extreme length of the large intestine which is 

 filled with a large amount of fecal debris makes them difficult 

 animals with which to work. Routine examination of normally 

 passed feces with additional examination following a purge are the 

 only practical means that can be employed for detecting infections 

 in pigs, since the cecum is so large that it is not practical to con- 

 sider collecting fecal material by enema. 



5. RABBITS 



The rabbit harbors at least three intestinal protozoa similar to 

 ones found in man. They are Chilojimstix cuniculi Fonseca, 191 5, 

 Giardia diiodenalis Davaine (1875) reported by Schwartz and 

 Shook (1929) to be pathogenic and the cause of ulcers, and an 

 amoeba of the E. coli type seen by Brug (1918) in rabbits and by 

 Rudovsky (1923) in hares. The writer also has observed this 

 amoeba recently in rabbits in Southern California. Little animal 

 transmission work has been attempted with rabbits but Huber 

 (1909) and Thomson (1926) report having established E. histoly- 

 tica infection in rabbits. 



There is a great need for careful morphological study and 

 animal-transfer experiments using the protozoa of the rabbit, since 

 so little has been accomplished to date in this field. The coccidia of 

 rabbits have attracted much more attention because of their asso- 

 ciation with liver and intestinal coccidiosis. It is surprising in this 



