TRICHOMONAS HOMINIS: INCIDENCE 



unharmed within an hour after being injected into the 

 stomach. 



Other investigators have recently confirmed these re- 

 sults. Thus Brumpt (1925) has reported the infection 

 of cats by the ingestion of trophozoites of Trichomonas 

 felis and Wenrich and Yanoff (1927) have shown that 

 four species of rat trichomonads and one species from 

 man may likewise be infective in the trophozoite stage. 

 The species studied were T. muris, T. parva, T. minuta, 

 and Pentatrichomonas sp. of the rat and Pentatricho- 

 monas from man. Cysts are known to occur in the life- 

 cycle of T. muris and were found also by Wenrich and 

 Yanoff in T. mimifa but the trophozoites of these species 

 are evidently infective as well as the cysts. 



Incidence of infection. The chances of the trophozoites 

 being ingested before they are killed by conditions outside 

 of the body are no doubt less than those of cysts and 

 probably account for the low incidence of infection with 

 this species reported in various surveys. Wenyon's 

 ( 1926) statement that ''Trichomonas hominis is probably 

 the commonest intestinal flagellate of man" is contrary 

 to the results reported by most investigators. The in- 

 cidence of infection is certainly much greater, however, 

 than the data available show. This is probably due to the 

 fact that most of the studies have been made with stools 

 that were many hours old. For example, Boeck and Stiles 

 (1923) report an incidence of only .07 per cent of T. 

 hominis from 8,029 individuals, but much of their mate- 

 rial was sent to them by post frorn considerable distances 

 (from 22 States). There are no cysts to reveal infection 

 143 



