PRESUMPTIVE TEST FOR BACILLUS COLI 



293 



B. coll. When 2 . 5 per cent of the salts were used the bacteria were 

 killed by the bile acids and considerably reduced by glycin, while the 

 results with the bile salts remained about the same. 



It is evident that the bile salts and especially their acids exert a 

 strong restraining action on the common bacteria which grow at blood 

 heat, and that except for glycin (which mildly restrains much as a sugar 

 retards bacterial action), the actual bactericidal effect lies in the 

 cholic acid radical of these salts. 



It is evident, therefore, that either of the bile salts or a mixture of 

 both salts may be employed, thus greatly reducing the cost and ease 

 of preparation of what would otherwise be a medium impracticable 

 for use in laboratories where much water work is carried on. In fact 

 it allows of the use of plain bile as a liquid restraining medium. 



In order to determine whether or not this restraining action is selec- 

 tive, a series of waters and solutions were made containing varying 

 numbers of intestinal bacteria. The following table gives the results 

 obtained : 



TABLE 2. 



COMPARISON OF RESULTS FROM VARIOUS BILE AGAR MEDIA. 



The media used in the experiments shown in the foregoing table 

 were made from fresh ox bile instead of the usual meat infusion with 

 peptone. The best results were obtained when the bile was not diluted. 



The figures show that a strong restraining action is exerted against 

 the growth of the common bacterial flora and to little or no extent 

 against certain of the fecal bacteria. 



The test for fecal bacteria is an important matter, especially in 

 water analysis. The method generally employed at the present time 

 for routine work was devised by Dr. Theobald Smith, 6 - 7 ' 8 and con- 



