226 RESEARCH IN PROTOZOOLOGY 



among pigs in Baltimore. Among guinea-pigs the incidence of in- 

 fection depends on the source from which the animals are secured ; 

 sometimes almost all of a number of specimens may be infected 

 and at other times none or only a few. Qean guinea-pigs can be 

 infected by feeding them cysts. The trophozoites of balantidia 

 from pigs will live in the cecum of rats for at least several weeks 

 when injected by laparotomy (Schumaker, 1929) and will persist 

 for at least several days in the ceca of young chicks when injected 

 per rectum (Hegner, 1929). Balantidia from both pigs and guinea- 

 pigs can be maintained in artificial media in test tubes. Many 

 species of balantidia have been reported from frogs and Wenyon 

 (1926) states that frogs are "nearly always infected," but little 

 success has been had in obtaining specimens from these animals 

 in the United States. Only in certain tropical regions can balan- 

 tidia be obtained readily from man or from monkeys. Cysts seem 

 to be rare in man, rare in pigs, at least at certain times of the year, 

 not so rare in monkeys, but common in guinea-pigs. 



OBTAINING AND PREPARING MATERIAL FOR STUDY 



a. Obtaining material. Pig. B. coli can be obtained from pigs 

 in slaughter houses at almost any time. A glass fruit jar or 

 vacuum bottle, piece of cheesecloth, and microscope, either a com- 

 pound microscope with low power objective, or better, a binocular 

 microscope, should be available. The vacuum bottle may be rinsed 

 out with water at body temperature (37° C.) before use so as to 

 prevent any cooling of the intestinal material put into it. The 

 ciliates are most abundant in the cecum and upper three feet of 

 the colon. The cecum is a sort of dilated pouch into which the 

 small intestine opens. In the cecum there may be as many as 

 120,000 balantidia per cubic centimeter; fewer trophozoites usually 

 occur in the colon, which is about six to eight feet long. Some 

 trophozoites escape in the feces probably because the fecal material 

 is often soft and moist. Cysts may be looked for in the lower part 

 of the colon but are difficult to find, if present, because of the large 

 number of worm eggs and debris in the contents. The cecal or in- 

 testinal material should be strained through cheesecloth into the 

 container to remove larger particles ; it is then ready to be trans- 

 ported to the laboratory. There is no evidence that lesions are 

 produced in the intestinal wall of the pig hence the procuring of 

 tissue is not necessary. 



