64 RESEARCH IN PROTOZOOLOGY 



Having determined that the suspected organisms are coprozoic 

 the next problem which presents itself is that of identification. 

 This can be accomplished only by careful study of the organism 

 living and in stained preparations coupled with reference to the 

 standard works on protozoa. Calkins Biology of the Protozoa 

 (1926) contains a most helpful key for the identification of un- 

 familiar forms. If the organism appears to be a new species its 

 life history should be ascertained. Most of the coprozoa so far 

 described live readily upon any nutrient medium which will main- 

 tain the fecal bacteria with which they were associated. It is well 

 to try to cultivate unknown amoebae or flagellates both on solid 

 and liquid media. The solid medium is more suitable for amoebae 

 whereas the liquid media are correspondingly adapted for flagel- 

 lates. If the organism has both an amoebic and flagellate stage this 

 may be demonstrated by an alternation in the use of liquid and 

 solid media. Life history studies should always be based upon 

 observations of a pure line or clone, that is, descendants of a single 

 individual. Single individuals may be isolated with a micropipette 

 or a very fine glass bristle at the end of a rod or by diluting cul- 

 ture medium enough so that a single drop examined on a coverslip 

 contains a single individual. The coverslip may be dropped into a 

 test tube of fresh culture medium, thus starting a pure line. The 

 conditions influencing the change from the amoebic phase to the 

 flagellate phase, if such an alternation occurs, should be noted; 

 also the factors inducing encystment. 



The evolutionary significance of the coprozoic protozoa is some- 

 what problematical and ofifers an excellent field of investigation. 

 It is generally believed by protozoologists that entozoic protozoa 

 are simply free-living forms that have migrated into some other 

 animal's body and have become thoroughly adapted to that habitat. 

 It is easy to conceive that a protozoon normally free-living that 

 has learned to tolerate the conditions of the intestine of an animal, 

 particularly the warm-blooded vertebrates, is taking the first step 

 toward the adoption of the entozoic habit. It seems very probable 

 that Hexamita occurs as a coprozoon and also as a harmless com- 

 mensal. The organism recently described by Cleveland (1928) is 

 also interesting from this point of view. The flagellate in question, 

 Tritrichomonas fecalis Cleveland, 1928, was isolated repeatedly 

 from the stools of one individual. The organism could not be 

 found or cultivated until approximately four weeks after the stool 



