OF THE ALIMENTARY TRACT 23 



hosts and the opportunity to be swallowed by an- 

 other person. The failure of an intestinal species 

 to encyst indicates that it is able to survive this period 

 of external exposure in the vegetative form, and, also, 

 to pass down the alimentary tract to its natural 

 habitat unharmed by secretions above. This pas- 

 sage of the stomach by Trichomonas in active form 

 we know takes place. 



The non-encysting must necessarily be transferred 

 in liquid or moist medium, consequently we may sus- 

 pect the commonly ingested liquids or moist foods 

 which are not heated in preparation. The observa- 

 tion (Lynch, 1926) that Trichomo7ias is a common 

 parasite of warm regions and rural populations and 

 uncommon in colder climates and urban and institu- 

 tional inhabitants is in support of this belief. 



It seems readily appreciable that the prevention 

 of contamination of water and other liquids and fresh 

 moist foods, or sufficient refrigeration, or, on the con- 

 trary, the heating of them to a degree sufficient to 

 kill vegetative forms w^ould bring about the elimina- 

 tion of unencysting intestinal protozoa as human 

 parasites. Modern measures of sanitation, sewerage 

 disposal, control of drinking water and milk, seem to 

 be sufficient for the purpose and to be responsible for 

 the low incidence of Trichomonas in people of such 

 hygienic environment. 



The species which are transmitted in the encysted 

 state offer a different problem. Certain institutional 

 surveys, notably by Thomas and Baumgartner 



