VI42-18 MANUAL OF METHODS FOR PURE CULTURE STUDY 



For hemolytic streptococci, the addition of serum to the broth 

 enhances hemolysin production. 



Method III. Filtrates. The hemolysin produced by some bacteria oc- 

 curs free in the broth in which the organism has been growing. Its 

 presence can be demonstrated by adding a sterile filtrate (Berkfeld or 

 Seitz filtrate) of the 12 to 18 hour culture to a 5% suspension of the 

 sterile blood or of suitable washed erythrocytes. 



Excessive exposure to air may inhibit or destroy the hemolytic 

 activity of the filtrate. (See Shwachman, Hellerman, and Cohen, 

 1934.) 



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