424 Vniversiiy of California Puhlications in Zoology [Vol. 20 



in appearance. As ovir rats have carried the infection of E. dysen- 

 teriae for five months, it seems highly probable that amoebiasis in 

 rats is inclined to become chronic, as it is in man. 



IV. Morphological Constancy of Parasites in Cross-Infection 



Experiments 



While many protozoologists hold to the theory that the different 

 species of amoebae common to the digestive tract of man are constant 

 in their morphological characters, respectively, yet there is an idea 

 among certain pathologists that the morphological characteristics of 

 amoebae may alter as the amoebae are transferred from one environ- 

 ment to another. 



During this investigation Endamoeha dysenteriae, Endamoeha 

 coli, Councilmania lafleuri, Eyidolimax nana, and lodamoeba butschlii 

 have been successfully transferred from man to rodents. During the 

 period of infection, which was five months in the case of E. dysenteriae 

 and four months in the case of the other species of amoebae, no 

 perceptible morphological change was noted in any of the species 

 used in the experiments. These facts afford valuable evidence in 

 favor of the morphological constancy of given species of amoebae, 

 at least of the failure of immediate change through transfer. 



D. SUMMARY 



1. Infections of five species of human intestinal amoebae, End- 

 amoeha dysenteriae, Endamoeha coli, Councilmania lafleuri, Endo- 

 limax nana, and lodamoeha biitschlii have been experimentally 

 transferred to rats by feeding them human faeces containing cysts 

 of these amoebae. 



2. Infections of E. dysenteriae and C. lafleuri have been experi- 

 mentally transferred to mice by feeding them human faeces containing 

 cysts of these amoebae. 



3. The percentage of rodents that have become infected with these 

 five amoebae common to man, is greater among young amoeba-free 

 animals than among old amoeba-free animals, or among young animals 

 known to possess an infection of amoeba common to the rat and 

 mouse. 



