150 University of California Publications in Zoology [Vol. 20 



multiply in the human stool after its evacuation from the bowel, and 

 that the stool may be inoculated either after evacuation by cysts from 

 dust or water, or by living tlagellates in hospital receptacles, or by 

 cysts which have safely passed through the intestine but have not 

 developed at body temperatures. It may well be that the reports of 

 C. hominis by Fantham and Porter (1916) and of C. parva by the 

 former, and by Porter (1918), and by other competent protozoologists, 

 rest upon the coprophilic basis, rather than upon a parasitic one. 

 There has been as yet, however, no adequate evidence presented to 

 establish the presence of either the living Cercomonas or of their cj^sts 

 in fresh stools in numbers characteristic of parasitic infections. While 

 it may be that Cercomonas is represented by a parasitic species in the 

 human intestine, a survey of the literature shows that the evidence 

 thereof is quite unconvincing. 



4. It is possible that the uniflagellate phase of Craigia hominis 

 (Craig) which does occur in fre.sh human stools (Craig, 1911, and 

 Barlow, 1915) might be mistaken in fresh preparations for Cercomonas. 

 Craigia usually lacks the tapering posterior end of the species of 

 Cercomonas, but may sometimes be attenuate posteriorly. In stained 

 preparations it shov,-s an unusually large central karyosome which is 

 not characteristic of Cercomonas. It is likewise accompanied by the 

 amoeboid stage and sometimes by the multiple encysted phase in the 

 human stool. The possibility of the confusion of Craigia with Cerco- 

 monas in much of the literature should be borne in mind. 



Prom a consideration of the points above enumerated we conclude 

 that there is no proof that Cercomonas is represented among the 

 human intestinal flagellates, though it may occur in the human 

 coprozoic faima. The species thus found are Cercomonas longicauda 

 Dujardin and C. parva Hartmann and Chagas. The species Cerco- 

 monas hominis Davaine is not today recognizable as a member of the 

 genus Cercomonas in human stools. Davaine's (1860) forms belong 

 to other genera, as we shall show later. 



It is highly desirable that all flagellates reported as Cercomonas 

 by any investigator of human flagellates or disease associated there- 

 with, be carefully worked out from stained preparations and accur- 

 ately figured, that cultures be attempted, and that necessary precau- 

 tions be taken to determine whether the flagellate has a coprozoic or 

 a parasitic .source. 



