496 University of California Publirafions in Zoology [Vol.20 



acid than the contents of the ileum or the colon. Determinations of 

 the pH by us in this experiment verify this conclusion and it would 

 seem that a definite chemotropism restricts the active amoebae to this 

 region. 



The degree of infection varies greatly ; in some instances as many 

 as three or four amoebae have been found in a single field of a freshly 

 prepared smear, while in other cases only a single amoeba has been 

 found in an entire smear. There is no evidence that the degree of 

 infection varies in difi'erent parts of the caecum, for if amoebae are 

 present in a smear from one region they are usually present in other 

 parts of the caecum. They may be scraped with caeeal contents from 

 the surface of the epithelium, but no visible pathological conditions 

 have been observed in the wall of the caecum. 



Food and pathogenicity. — The amoebae live normally upon food 

 procured from the contents of the caecum. They may ingest bacteria 

 (pi. 43, figs. 1, 2), yeasts, and flagellates (pi. 43, fig. 4), as shown by 

 the presence of a partly digested Chilomastix in the largest vacuole. 

 At the .suggestion of Dr. I. C. Hall of the Department of Bacteriology- 

 in the Univer.sity of California, gram stains were made of the free 

 amoebae from the caecum in order to determine the type of bacteria 

 ingested. After a number of attempts, successful results were obtained. 

 Bismark brown was found to be the most successful counterstain. The 

 cytoplasm is gram-negative while the nucleus retains the gentian violet. 

 The amoebae ingest both gram-positive and gram-negative bacteria, 

 the cases examined giving 75 per cent gram-negative rods and 25 per 

 cent gram-positive cocci. It is significant that no gram-positive rods 

 have been found ingested, though many are present on the slides in the 

 material surrounding the amoebae. Whether or not a change in the 

 .stainability of the bacteria is produced by their partial a.ssimilation 

 by the amoebae which causes them to stain gram-negative, it is as yet 

 impossible to say. Sphaerita (Dobell, 1921) has been found as a 

 parasite in the amoebae (pi. 43, fig. 1). 



Because no evidence has been encountered which indicates that 

 the free amoebae ingest normal tissue cells — the reason being that no 

 caeeal ulcers have been found in any of the rats — and because 34 per 

 cent of normal rats harbor amoebae in the caecum, it is thought that 

 no pathogenic results accompany the presence of these amoebae in 

 the rodent hosts. 



Pseudopodia and amoeboid movement. — As examination in normal 

 saline reveals no marked specific difi'erences between Counciimania 



