A NEW SOLUTION FOR THE PRESUMPTIVE TEST 

 FOR BACILLUS COLL* 



Daniel D. Jackson. 



{From Ml. Prospect Laboratory, Brooklyn, N. F.) 



MacConkey "•'•' has pointed out that the intestinal bacteria grow 

 well on an agar medium containing o . 5 per cent of sodium tauro- 

 cholate, while the common bacteria are to a great extent excluded, 

 and he has recommended that this medium be used to distinguish 

 between B. coll and B. typhi ahdominalis and also as a test for fecal 

 contamination in water. Jordan, Russell, and Zeit,-* in experiment- 

 ing with this medium for testing water, did not obtain very favorable 

 results in that the medium failed to eliminate all of the water forms. 

 Robin^ has used MacConkey's agar to advantage in tests of filters; 

 but while the results were preferable to those obtained on the regular 

 agar, it could not be concluded that all the bacteria found, or a definite 

 percentage of them, were always of fecal origin. 



In order to determine the germicidal action of the bile salts and 

 their constituents, the author has used a standard agar medium with 

 an addition of varying amounts of these salts, and noted the effect 

 produced. The following are the results obtained with the bile salts, 

 and their constituents upon the agar growth at 37° C. of bacteria from 

 a slightly contaminated water containing two B. coli per c.c. 



TABLE I. 



Sodium taurocholate 



" glycocholate 



Taurocholic acid. . . 



Glycocholic add. . . 



Cholic acid 



Taurin 



Glycin 



Plain Agar 



20 

 20 

 20 

 20 

 20 

 20 

 20 



Agar +0.05% 



14 

 14 

 10 

 12 



14 

 20 

 19 



Agar +0.5% 



4 

 2 

 2 



S 

 2 



19 

 II 



Agar + 2.5% 



2 



2 

 o 

 o 

 o 



20 



s 



This table shows that the bile acids reduced the number of bac- 

 teria even when only o . 05 per cent was taken, and that when o . 5 

 per cent was employed, taurocholic, gylcocholic, and cholic acids, 

 sodium taurocholate, sodium glycocholate, and glycin greatly reduce 

 the bacteria present, some of those remaining giving the tests for 



* Received for publication April 12, 1906. 



292 



