118 INTESTINAL FLAGELLATES AND CILLATES 



the general form of the body and in the possession of a parabasal 

 body and an undulating membrane, but have an additional free 

 flagellum. In Cercomonas (Fig. 29C), according to Wenyon, 

 the trailing flagellum is attached to the side of the body as far 

 as the posterior end, usually being continued as a free flagellum. 



Fig. 29. Bi-flagellated parasites. A, Bodo; note absence of parabasal body. 

 B, Prowazekia; note parabasal body (par. b.). C, Cercomonas; note trailing 

 flagellum attached to side of body. This is not recognized as a flagellum by some 

 workers. X 2000. (After Wenyon.) 



According to others Cercomonas has only a single flagellum, the 

 free one at the anterior end. Bodo and Prowazekia (Fig. 29 A and 

 B) both have two flagella, one waving anteriorly, the other trail- 

 ing behind; Prowazekia differs from Bodo, and also from Cercomo- 

 nas, in having a parabasal body. 



Of these parasites only Prowazekia, of which several poorly 

 defined species have been recorded from man, can be considered 

 a true human parasite; Bodo and Cercomonas, as found in freshly 

 passed faeces, are probably free-living forms which have been 

 ingested accidentally as cysts with water or food. Wenyon 

 states that all three genera grow readily in cultures a«id form 

 small round cysts, two to eight fi (yj—^ to ^^^^ of an inch) in 

 diameter. They probably all pass through an ameboid stage in 

 which they are indistinguishable from the small amebse of the 

 " Umax " group. 



Multi-flagellate Intestinal Protozoa 



Trichomonas intestinalis. — Of the several flagellates which 

 have been found in the human digestive tract and fseces, Tricho- 

 monas is the commonest. It makes its home in the upper 



