422 University of California Piiblicaiions in Zoology [Vol.20 



Certain experimental studies cited in this paper, together with the 

 results of this investigation, lead to the conclusion that transfer is 

 possible at least in certain instances or under given conditions. With 

 reference to E. dysenteriae, all attempts prior to 1915 to infect rats 

 with this species of amoeba failed. In 1915 Lynch appears to have 

 succeeded in infecting rats with E. dysenteriae. Since 1915 four 

 other attempts have been made to infect rats and mice with this same 

 species of amoeba, but, prior to the present investigation, only one 

 has been successful, and that with one rat only. It seems likely that 

 the failures have been due to using an insufficient number of animals, 

 especially of young, amoebae-free individuals. 



In the present investigation successful infection of rodents with 

 E. dysenteriae has been accomplished in thirteen rats and one mouse, 

 with E. coli in seventeen rats, with Council mania lafleuri in twenty- 

 three rats and one mouse, with EndoUmax nana in two rats, and with 

 lodamoeba hiitschlii in two rats (pis. 38-39). 



This successful transference to rodent hosts of the amoebae com- 

 monly parasitic in the digestive tract of man is evidence in favor of 

 a certain degree of promiscuity of infection of a given species of 

 parasite in several species of host, provided the conditions for suc- 

 cessful infection are met. 



II. Factors Involved in Establishment of Parasitic Infection 

 BY Amoebae 



The varj'ing factors in establishing an infection of amoebiasis 

 in the rodent host appear to be (1) the viability of the cysts used 

 in feeding, and (2) the age of the rodent host, together with (3) 

 its active resistance to an amoebic infection. 



In some cases large numbers of living amoebic cysts were fed 

 to young rats without successful infection, e.g., Rats 1, 2, 3, and 4 

 in table 1, while in other cases small numbers of amoebic cysts 

 were fed to a series of rats one time only and successful infection 

 resulted, e.g.. Rats 49, 54, and 62. It seem.s probable that the cysts 

 in the second case were more viable than those in the first case. 



Young amoeba-free rodents have acquired an amoebic infection 

 in 80 per cent of the cases fed, while young rodents known to harbor 

 an amoebic infection of amoebae normal to rats and mice have 

 acquired a further amoebic infection in only 15 per cent of the cases. 

 Thus, young amoeba-free rodents are more susceptible to amoebic 

 infection than voung rodents with a known amoebic infection. 



