with various concentrations of the bril- 

 liant green. Four cultures of B. aero- 

 genes and five of B. coll were employed 

 with the following results : 



With a dilution of 1-100,000 of bril- 

 liant green, none of the B. coli grew at 

 all. All of the B. aerogencs grew, but 

 the colonies were only half as large as 

 the controls indicating a marked inhibi- 

 tion. With 1-200,000 dilution, B. coli 

 still failed to grow whereas B. aerogenes 

 grew reasonably well, but not as lux- 

 uriantly as the controls. With 1-300,000 

 of the dye, three of the B. coli still failed 

 to show any evidence of growth and two 

 others grew very poorly. All the aero- 

 genes showed a very heavy growth. With 



1-400,000 brilliant green, the growths of 

 B. aerogenes were as luxuriant as the 

 controls, whereas 2 cultures of B. coli 

 failed to grow and the three others 

 showed very small, stunted non-char- 

 acteristic colonies. 



In conclusion, it may be said that these 

 preliminary studies indicate that the con- 

 centration of peptone exerts a marked 

 influence on the inhibitory action of dyes 

 in culture media, and that it appears 

 feasible to devise both liquid and solid 

 media which will inhibit B. coli. but not 

 B. aerogenes. The most promising in- 

 hibitory agent which we have as yet en- 

 countered for this purpose is 'brilliant 

 green. 



