1924] Kessel: Amoihac of Culture Rais diid Mice 517 



The nuclei in the resting stage simulate very closelj- the typical 

 nuclei of E. coll (pi. 48, figs. 58-62). The nuclear membrane is dis- 

 tinct and may or may not be encrusted with chromatin granules. The 

 karyosome is in the form of a small but distinct excentrie sphere. The 

 diffuse, excentrie karyosome and the heavy, peripheral chromatin blobs 

 found in C. decumani have not been seen in this species. The binu- 

 cleate cysts (pi. 48, fig. 59) have a large glycogen vacuole similar to 

 the type found in E. coli, but the chromatoidal bodies (fig. 60) are 

 more massed than in the type usually found in E. coli. 



No evidence of budding has been found in the cysts thus far 

 encountered. 



The average diameter of the cysts in this species is 14.6/*. This 

 is much smaller than the average diameter of the cysts of E. coli which 

 is 17.3ja. 



The conclusions to be drawn at the present time from the study of 

 this species is that it differs from E. coli with respect to size, and in 

 the massing of the chromatoidal bodies. 



Endamoeha coli that have passed through rats during this investi- 

 gation maintain the structural and size differences mentioned above 

 and it is on this basis that E. ratti is differentiated from E. coli. 



EXPERIMENTS IN CROSS-INFECTION 



While careful study of the stained material at hand indicates 

 decisively that Councilmania mwis and C. decumani are distinct 

 species, in the light of the successful infection of rats with the amoebae 

 of the human intestinal tract (Kessel, 19236) in which transfer the 

 amoebae underwent no visible morphological change during the period 

 of the experiment, cross-infection of C. muris and C. decumani was 

 attempted from rats to rats, from rats to mice, from mice to mice, and 

 from mice to rats. The results are tabulated in the accompanying 

 tables. 



In this experimental work the amoeba-free rats and mice were 

 chosen by the epsom salt method as in the other infection experiments 

 carried on in this investigation. As very young amoeba-free mice 

 were not always on hand, it was necessary in most ca.ses to use old mice. 

 It has been found throughout this investigation that old rats and mice 

 are less susceptible to infection than young stock. This suggests that 

 the older animals are able to establish an active immunity against 

 infection. In the series of experiments in attempting to transfer C. 



