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H. R. BAKER 



and incubated at 37°C. for forty-eight hours to render the medium 

 sugar-free. Then the medium was sterilized in the Arnold for 

 twenty minutes; 10 grams of peptone and 5 grams of sodium 

 chloride were added; the reaction was adjusted to pH 7.0 with 

 brom-thymol-blue; the medium was again steamed for twenty 

 minutes, the reaction readjusted, and the medium filtered. 



To determine the amount of brom-thymol-blue which would 

 inhibit acid production by microorganisms, fifty cubic centi- 

 meters of sugar free broth were placed in each of fifteen flasks. 



TABLE 1 



The influence of brom-lhymol-hlue upon acid production by Bad. coli-communis. 

 Using 1 per cent glucose broth, initial pH 7.0, increasing amounts of a 0.2 per cent 

 alcoholic solution of brom-thymol-blue inoculated u^lh 0.1 cc. of an eighteen hour 

 broth culture 



— = No acid production; + = moderate acid production; ++ = strong acid 

 production. 



To each flask was added sufficient 0.2 per cent alcoholic solution 

 of brom-thymol-blue to give the concentrations as shown in the 

 tables. Equal amounts of the media were placed in five test 

 tubes of similar size, and the tubed media were sterilized in the 

 autoclave at 18 pounds pressure for twenty minutes. 



When the tubes were cold, one cubic centimeter of a sterile 

 20 per cent glucose solution was added, under aseptic conditions, 

 to each tube. The tubes were incubated at 37°C. for forty-eight 

 hours, in order to make certain that none of them became con- 

 taminated during the process of adding the glucose solution. 



