526 Univen-iti) of California Publirations in Zoohc/ij [^'ol- 20 



acteristic of the species belonging to the genus Coitncilmania found 

 in the rat. On the other hand, Endamoeha coli is not so easily affected 

 by the change of environment and may continue its activity in normal 

 saline on the warm stage for several hours (Kofoid, SM'ezy, and Kessel, 

 19236). 



Evolutionary source of infection of CouncUmania of man. — The 

 source of the infection of the parasites of man is an important prob- 

 lem. While it is impossible to state in all instances the source from 

 which man originally acquired his para.sitie infections, the evolution- 

 ary origin of certain protozoan infections is at least suspected. 

 lodamoeba biitschlii has been described as occurring in the pig and 

 it is suspected (Kofoid, 1923) that man acquired his original infection 

 from that source. The wild game in Africa is thought to be the source 

 of infection to man of the causative organisms of African sleeping 

 sickness and Reichenow (1920) has recently claimed that monkeys 

 are a dangeroas source of infection to man, of the organisms causing 

 malaria. 



Rats and mice have long since been regarded as among the most 

 annoying pests of mankind. On account of their tendency to inhabit 

 the dwelling places of the human race, they have from earliest times 

 doubtless been brought into very close proximity with the substances 

 used by man for food. It seems very likely that these rodents may 

 also have fi^mctioned in the evolutionary origin of man's parasitic 

 C ouncilmania in the past (Kofoid, 1923). 



The remarkable similarity between the species of amoebae belong- 

 ing to the genus CouncUmania found in man and the two species of 

 that genus found in rats and mice leads one to suspect that these 

 animals may be the original source of infection by the genus Council- 

 mania in man; i.e., man may have originally acquired his infection of 

 this species of amoeba from rodent hosts. This suspicion leads one to 

 the consideration of the question of the obligate specificity between 

 host and parasite which has been discussed by Kessel (19236). The 

 successful experimental transfer of C. muris and C. decumani recorded 

 in this paper affords valuable evidence against the specificity of 

 parasitic amoebae to a given host. 



Immunity. — The question of the establishment of an active immun- 

 ity to amoebiasis is a new one. No experimental work with respect to 

 this question has been done with the amoebae of man. Yet, in the 

 examination of rats during this investigation, the question of the 

 possibility of certain animals being immune to infection has presented 

 itself on several occasions. 



