HOST-PARASITE RELATIONS I INTESTINAL PROTOZOA 



hominis to be 49° C. These temperatures are higher than 

 any the flagellates would ordinarily encounter in nature. 



Favorable conditions for transmission. Although Tri- 

 chomonas hominis reaches new hosts in the trophozoite 

 stage the locomotor powers of the flagellates play no 

 part in transmission ; that is, the flagellates are passively 

 conveyed to new hosts in various ways but not by their 

 own activities. A moist climate is particularly favorable 

 since fecal material does not dry as rapidly and rains 

 may dilute the feces or wash the flagellates into ponds 

 or streams that are sources of drinking water. It is prob- 

 able that T. hominis will live longer in diluted than in 

 raw feces as is true of the cysts of certain other intestinal 

 protozoa (Boeck, 1921b). Insanitary conditions are also 

 conducive to transmission. Flies and possibly other in- 

 sects that visit both fecal material and human food and 

 drink play a role of undetermined importance in the 

 transfer of the flagellates. Wenyon and O'Connor 

 (1917) found that living, motile trichomonads were 

 present in the droppings of flies 5 minutes after being fed 

 on infected feces, which is an interval sufficiently long 

 to allow the flies to carry the organisms a considerable 

 distance. The host, therefore, brings about his own infec- 

 tion without any effort on the part of the trichomonads 

 and entirely because of insanitary habits. Cleanliness, 

 the prevention of soil pollution, the screening of fecal 

 material from flies and other insects, and the abolition of 

 infected food handlers would do much to lower the inci- 

 dence of infection. 



(2) Distribution and localization within the 

 HOST. The digestive tract. It is evident that the tropho- 



146 



