HOST-PARASITE RELATIONS I INTESTINAL PROTOZOA 



resistant to yatren and emetin; they withstood 5 per 

 cent HCl for 30 minutes, but were not very resistant to 

 various disinfectants. 



Condusioiis regarding the disinfection of feces, milk, 

 and drinking water. As a result of these various experi- 

 ments we may conclude that a simple method of disinfect- 

 ing feces containing histolytica cysts is available, namely, 

 the use of cresol in a strength of i in 20, but that no 

 practical method has yet been discovered of sterilizing 

 drinking water. The pasteurization of milk probably 

 raises the temperature to a high enough point (60° C.) 

 for a sufficient time to destroy any protozoan cysts pres- 

 ent and of course the boiling of water would quickly kill 

 all cysts. 



2. Avenue of infection. How do living cysts of E. 

 histolytica reach the digestive tract of man? There is 

 only one conceivable method of entrance, in nature, and 

 that is by way of the mouth. It seems probable that they 

 usually reach the mouth in contaminated food and drink 

 but they might also find their way there on soiled hands. 

 Among the most important factors that bring about the 

 dissemination of cysts, and especially their presence in 

 food and drink, are probably the handling of food in 

 homes, restaurants, hotels and markets by infected per- 

 sons who are passing cysts; the use of night soil as 

 fertilizer in vegetable gardens ; the common use of toilet, 

 washbowl, and towel ; and the presence of insects, such as 

 flies, ants and cockroaches, and of domestic animals, such 

 as rats, mice, dogs and cats. 



The dissemination of cysts by flies. That flies may play 

 an important role in the dissemination of histolytica and 



74 



