50 PROTOZOAN PARASITISM 



rats a natural intestinal infection with an amoeba 

 agreeing very closely in its morphology with End- 

 amoeba histolytica of human origin. These three, 

 as well as Kessel (1923), also infected rats by feeding 

 human feces containing the cysts. The rat is an 

 omniverous animal and will eat human feces even 

 when other food is available. In many places this 

 animal has access to human excreta and opportunity 

 to contaminate human food and eating utensils with 

 its own excreta. These opportunities are uncommon 

 under modern housing and sanitary conditions, but 

 there are many places where they are not uncommon 

 and these are the places where intestinal amoebiasis 

 is usually most common and important. Until 

 studies are made in such regions and it is shown that 

 the rat does not transmit the infection in nature, this 

 animal must be under suspicion as a possible carrier. 



Under similar suspicion is the domestic pig, since 

 Kessel (1928) has reported that this animal may 

 naturally and experimentally harbor this amoeba for 

 about six weeks. In some quarters the pig is in close 

 contact with human beings and is allowed access 

 to human excrement. 



Using the culture method to prove the viability of 

 cysts, Yorke and Adams (1926) found that Endam- 

 oeba histolytica cysts commence to die fairly rapidly 

 in feces at laboratory temperature (16-20°C.) for 

 three or four days and that all died within ten days. 

 This was also the case at 0°C. They found, also, 

 that the cysts survive a temperature of 45 °C. for 



