io8 RESEARCH IN PROTOZOOLOGY 



of material from the part of the intestine inhabited by protozoa 

 have been successfully employed in studies on the effects of 

 changes in diet on the trichomonads of rats. Such methods seem 

 almost essential in investigations of this sort. They allow observa- 

 tions on the protozoa as they live in the intestine with minimum 

 disturbance to intestinal conditions. They are also apphcable to 

 the study of other protozoa of the rats and, with modifications, to 

 similar studies on the intestinal protozoa of other laboratory ani- 

 mals. In the experiments on the trichomonads of rats 0.2 of a 

 cubic centimeter of material was removed from the cecum, and 

 diluted in 0.8 of a cubic centimeter of 0.85% sodium chloride 

 solution, care being taken to insure thorough mixing and break- 

 ing up of all masses of material. From this dilution one cubic 

 centimeter was transferred to nine cubic centimeters of saline to 

 serve as a base for further dilution in typing and enumerating the 

 bacteria. The remaining cubic centimeter was used for trichomonad 

 counts and pH determinations. The flagellates were counted in a 

 Leitz blood-counting chamber, the organisms in the four groups 

 of large squares being counted and averaged. This was taken as 

 the number of protozoa per o.i cubic millimeter of a i :io dilution. 

 This figure multiplied by one hundred was taken as the number of 

 trichomonads per cubic millimeter of caecal material. The percent- 

 age of error is considerably less than ten per cent when infections 

 vary between 1,000 and 40,000 trichomonads per cubic milHmeter. 

 Heavier or lighter infections are rarely encountered. 



The pH was determined colorimetrically using a LaMotte 36 

 hydrogen-ion testing set. This method is not as accurate as elec- 

 trometric determinations, but is applicable when an electric ap- 

 paratus is not available. These measurements are of doubtful value, 

 however, considering what is known of the pH of media in which 

 intestinal protozoa are cultivated. 



The bacteria that should be considered are those types which 

 are known to respond to changes in diet, i.e., the lactose-ferment- 

 ing organisms, the aciduric bacteria and the anaerobes. All protozoa 

 that live in the lower intestine are probably influenced to some 

 degree by changes in bacteria due to dietary alterations. Those 

 that ingest bacteria. Trichomonas, Chilomastix, and Endamosha, no 

 doubt are more readily influenced, but certain bacteria probably 

 exert more influence through the substances they form from partly 

 digested food than through the numbers present. 



