406 University of California Publications in Zoology [Vol. 20 



times. The numbers found were small and it is probable that these 

 may have been forced from the caecum by the peristalsis induced by 

 the purge. 



It should be noted here that during this investigation rats which 

 were known to harbor infections of amoebae and which showed no 

 amoebae in faeces collected without the administration of a purge, 

 invariably showed amoebae in the caecum at autopsy, which followed 

 immediately after faeeal examination, though amoebae were not found 

 in the colon at autopsy. 



The general conclusions to be drawn from the above facts are as 

 follows : 



1. Faecal examination of rats on two consecutive days after they 

 have been purged with epsom salt is a comparatively safe method for 

 detecting the presence of amoebae and Trichomonas muris in these 

 animals. 



2. Amoebae common to rats and mice and Trichomonas muris 

 commonly inhabit the caecum of these animals. 



3. Giardia, muris, Hexamitus m.uris, and probably ChUomastix 

 inhabit the small intestine normally, and their presence in rodents 

 cannot always be detected upon examination of the faeces after 

 administration of epsom salt. 



Hegner (1923) has found a much higher percentage of rats 

 infected with Giardia miiris and Hexamitus muris than has been 

 found in this laboratory. It thus seems that the incidence of 

 infection for different Protozoa may vary greatly in different rodent 

 colonies. 



During the present investigation it has been found that it is much 

 more difficult to work with mice than with rats. In the first place, 

 mice will not eat the mixture of bread and salts so readily as the 

 rats will, and in the second place, it is more difficult to collect semi- 

 liquid faeces from mice than from rats. No table to determine the 

 accuracy of the epsom salt method for examining mice for Protozoa 

 has been compiled, but from a few examinations made it is concluded 

 that on account of the difficulty encountered in working with mice 

 the method cannot be relied upon as it can in the case of rats. 



