520 University of California Publications in Zoology [^'oi.. 20 



It is much more difficult to force mice to take epsom salt than it 

 is to induce rats to take it. Because of this fact, one is not always 

 certain that the experimental animal is amoeba-free, as is the case 

 with the experimental rats. Further, the salt method of obtaining 

 amoeba-free animals has not been conclusively tested with mice, as it 

 has with rats. Attempts to infect mice with the amoebae of the human 

 digestive tract have not met with the success that attended similar 

 infection experiments with rats. It is thus easily understood that 

 mice are much more difficult to work with than rats. The mixed 

 infection of the third attempt to tran.sfer C. muris from rat to mouse 

 may be therefore attributable to a probable previous infection of 

 C. decumani that had been overlooked in determining the amoeba-free 

 mice. 



Culture. — No success has attended our attempts to culture para- 

 sitic amoebae in artificial media. Although instances have been 

 recorded in the earlier works in which E. coli and E. dysenteriae are 

 supposed to have been cultured, it is now generally recognized that 

 the workers were dealing in their culture amoebae with non-parasitic 

 species (Dobell, 1919). In this investigation it was impossible to 

 engage in extensive attempts to culture amoebae from the rat, but 

 several brief endeavors were made. 



The first medium used was that recommended by Musgrave and 

 Clegg (1904), for E. coli. Attempts were made with an alkaline 

 medium in an anaerobic environment only and were unsuccessful. 

 Wenyon (1907) had previously tried this medium both aerobically 

 and anaerobically, but without success. 



In order to simulate more closely the environmental conditions of 

 the caecum in which the amoebae live in greatest numbers, at the sug- 

 gestion of Dr. T. D. Beckwith of the Department of Bacteriology of 

 this University, the hydrogen ion concentration of the caeca of several 

 rats was taken. The caeca of eight rats non-infected with amoebae, 

 and of eight rats that showed amoebic infection, were tested. The 

 average pH of the caeeal contents of both amoebae-free rats and of 

 rats with positive amoebic infection was 6.35. 



Rettger and Cheplin (1921) showed that the pH of the faecal 

 material from the caecum and colon ranged from 5.5 to 6.7 in the 

 various rats they tested. They failed to differentiate between the pll 

 of the caecum and other parts of the digestive tract. Furthermore, 

 their work was carried on in connection with the intestinal flora of 

 rats and no record was given of the presence or absence of amoebae. 



