490 University of Califoniia Publications in Zoology [Vol.20 



INTRODUCTION 



The present investigation was begun in order that, later, we might 

 attempt the experimental infection of rats and mice with the common 

 intestinal amoebae found in man. For it was early realized that, before 

 such critical experimental infections could be carried out satisfactorily, 

 a detailed study of the amoebae normal to the rat and mouse was 

 essential. 



Our attempts to culture in rats and mice most of the common intes- 

 tinal amoebae of man have met with success (Kessel, 19236), and it is 

 our purpose in the present paper to describe the distinguishing char- 

 acteristics of the amoebae normally occurring in culture rats and mice. 



HISTORICAL 



Grassi (1881) found in both the rat and the mouse an amoeba which 

 he named Amoeba muris. He published no figures and described no 

 cysts but stated that the motile forms resembled Amoeba coli (Losch) 

 in man. He distinguished the amoeba of the mouse from E. coli largely 

 on the basis of size, and stated that the maximum size of the species 

 found in the mouse slightlj' exceeds the minimum size of the species 

 found in man. 



Wenyon (1907) in connection with his work on the intestinal 

 Protozoa of mice made a careful study of an amoeba found in the 

 mouse, and concluded that the free forms and cysts bore a very striking 

 resemblance to Endamoeha coli. When the genus Councilmania was 

 later described (Kofoid and Swezj^, 1921), resemblances were at once 

 apparent between this new genus and the amoeba described by 

 Wenyon. These are also very well shown in Wenyon 's figures. 



Wenyon 's work is excellent as a pioneer investigation, but certain 

 structures, such as the chromatoidal body, were not then regarded as 

 important diagnostic characters and were described (his pi. 10, figs. 

 13, 20) as being remains of food products that had been thrown out of 

 the cyst. It is now generally accepted that solid food products are 

 extruded in the precystic stage. His account of autogamj^ in the 

 amoeba of the mouse, as previously described by Schaudinn for Enda- 

 moeha coli, cannot be upheld in the light of our present knowledge of 

 nuclear phenomena in cysts. 



