TRICHOMONAS HOMINIS! TRANSMISSION 



Host-parasite specificity. Trichomonads have been de- 

 scribed from the mouths of lower animals by Hegner 

 and Ratcliffe (1927a, 1927b). A species, named by these 

 investigators Trichomonas canistomcB, was reported from 

 22 of 23 dogs examined. Since this report was prepared 

 the twenty-third dog and 26 other dogs examined have 

 all been found to be positive; thus 100 per cent infection 

 existed in these 49 dogs from Baltimore. Trichomonads 

 were obtained also from the mouths of 2 cats ; these have 

 been named Trichomonas feiistomce (Hegner and Rat- 

 cliffe, 1927b). 



3. TRICHOMONAS HOMINIS 



(i) Epidemiology of transmission. Transmission 

 by trophozoites. As noted above, intestinal trichomonads 

 have been recorded with three, four, and five anterior 

 flagella. These may be considered varieties of the species 

 Trichomonas hominis (Fig. 9), or separate species of the 

 genus Trichomonas or representatives of different gen- 

 era, Tritrichomonas, Trichomonas and Pentatrichomonas 

 respectively ; but at present it seems best to discuss them 

 all as members of the species Trichomonas hominis. 



The problem of the transmission of the intestinal 

 trichomonads from one human host to another is par- 

 ticularly interesting because there is no cyst stage known 

 in the life-cycle of the species that live in man and, there- 

 fore, transmission must take place by the ingestion of 

 living trophozoites, usually, no doubt, in food or drink. 

 However, the prevailing idea, as already pointed out 

 (p. 65), is that trophozoites of intestinal protozoa are 

 destroyed in the digestive tract if swallowed. Wenyon 



141 



