TRICHOMONAS VAGINALIS 



large sucking disc bordered by anterior and posterior 

 peristomal fibers. Beneath the sucking disc are two oval 

 nuclei. A pair of slender axostyles extend through the 

 center of the body and four pairs of flagella arise as 

 shown in the figure. The posterior peristomal fibers and 

 the posterior lateral flagella delimit on either side a thick- 

 ened area, the lateral shields, between which is a diamond- 

 shaped region that thins out into a "tail." The cysts 

 (Fig. 13b) are oval in shape and average lo.yij, in length 

 and 7.47M in breadth. Cysts with 2, 4, 8 and 16 nuclei 

 occur ; they are spherical and are usually distributed two 

 near the anterior end, two near either end, four near 

 the anterior end or four near either end. Axostyles and 

 many of the fibrils present in the trophozoite persist in 

 the cyst. Frontal longitudinal division of the trophozoite 

 has been described (Kofoid and Swezy, 1922b) and 

 multiple fission has been reported (Noc, 1909). Excysta- 

 tion has recently been described (Hegner, 1927a). 



III. Host-Parasite Relations between Man and His 

 Intestinal Flagellates 



I. TRICHOMONAS VAGINALIS 



As in the case of intestinal amoebae there is no other 

 conceivable method of infection of the human host with 

 intestinal flagellates but by the ingestion of living tropho- 

 zoites and cysts. However, Trichomonas vaginalis and 

 T. huccalis, which are usually included with the intestinal 

 flagellates proper, must reach their primary sites of infec- 

 tion in some other way. These two species will be con- 

 sidered first, and then the other species described above. 



135 



