»Tuberculin conforms to the regulations of the FDAconcerning biologics (650.10to 650.15)(see
Biologics á1041ñ).It is a sterile solution derived from the concentrated,soluble products of growth of the tubercle bacillus (
Mycobacterium tuberculosisor
Mycobacterium bovis)prepared in a special medium.It is provided either as Old Tuberculin,a culture filtrate adjusted to the standard potency based on the U.S.Standard Tuberculin,Old,by addition of glycerin and isotonic sodium chloride solution,or as Purified Protein Derivative (PPD),a further purified protein fraction standardized with the U.S.Standard Tuberculin,Purified Protein Derivative.It has a potency,tested by comparison with the corresponding U.S.Standard Tuberculin,on intradermal injection of sensitized guinea pigs,of between 80percent and 120percent of that stated on the label.It is free from viable
Mycobacteriaas shown by injection into guinea pigs.