METHODS OF PURE CULTURE STUDY 



123 



Milk. Acid production in milk can be detected by adding 

 brom cresol purple to the culture and comparing with the color 

 obtained by adding the same proportionate quantity of indica- 



TABLE 1 



Degrees of acidity easily recognized in clear inedia 



* Use a 0.04 per cent alcoholic solution. 

 t Use a 0.02 per cent alcoholic solution. 



TABLE 2 



Degrees of acidity easily recognized in milk 



* Use a 0.04 per cent alcoholic solution. 



tor to sterile milk. (Brom thymol blue does not give satisfac- 

 tory results in milk.) Four degrees of acidity that can be simply 

 recognized in milk are hsted in table 2. They correspond 

 closely to those Usted in table 1, differing only in that brom 



