102 RESEARCH IN PROTOZOOLOGY 



pig generally agree that the encysted stages produce only a single 

 nucleus. Whether Smith (1910) was dealing with this amoeba or 

 with a different species is not quite certain, but on account of the 

 fact that Smith's amoeba penetrated the tissue the writer is in- 

 clined to feel that he was not dealing with the amoeba described by 

 Prowazek. Douwes (1921) figures a four-nucleate cyst of the 

 amoeba from the pig and Kessel (1928a) found an amoeba re- 

 sembling E. histolytica to be fairly common in pigs in Peking. 

 Morphologically, the trophozoites and cysts are indistinguishable 

 from Endanwcha histolytica. The amoeba was experimentally trans- 

 ferred to kittens which developed symptoms identical with those 

 kittens experimentally infected with Endamooba histolytica of man. 

 Young pigs reared under laboratory conditions were then experi- 

 mentally infected with Endama^ba histolytica of man by feeding 

 them cysts. The infection became established and four-nucleate 

 cysts were recovered from the pigs at intervals for several weeks. 

 However, without a satisfactory explanation both naturally and 

 experimentally infected pigs cleared themselves of the infection. 

 Whether there is a slight physiological difference between the En- 

 danmba histolytica of man and its cotype in the pig is not thor- 

 oughly demonstrated but it seems plausible to assume that the pig 

 may be a temporary and not a permanent host for Endamoeba his- 

 tolytica. Further experimental work is needed on this subject to 

 afford final conclusions. Other intestinal protozoa found in the pig 

 are lodamwba suis O'Connor (1920), Trichomonas suis Gruby and 

 Delafond (1843); types resembling Endolimax, Endama:ba coli, 

 Chilomastix and Bodo are described by Kessel (19280). Balan- 

 tidiuni coli has also long been recognized as the common parasite 

 of the domestic pig. Epidemiological and experimental evidence 

 collected to date by Walker (1913) and Brumpt (1909) supports 

 the hypothesis that Balantidium coli of man and of the domestic 

 pig are in reality the same species. Since the other kind of in- 

 testinal protozoa of the domestic pig with the exception of Enda- 

 mceba polccki resemble so closely in morphology a corresponding 

 type found in man, the writer is inclined to acknowledge them as 

 belonging to the same species as their representative types in man. 

 It must be remembered, however, that cross-infection experi- 

 ments with these protozoa of the pig to common laboratory animals 

 have not been done. Such are highly desirable and also other at- 

 tempts to infect pigs with the common protozoa of man should be 



