Spermine inhibits the multiplication of tubercle bacilli in vitro only if another tissue substance is present in the culture medium. This activating substance occurs as a chemical contaminant of the albumin in commercial bovine plasma fraction V ordinarily added to culture media; it is also found in whole bovine and sheep serum and in aqueous extracts of the guinea pig kidney. No detectable spermine activator is contained in whole human, guinea pig, or rabbit serum.
The serum constituent which renders spermine inhibitory for the growth of acid-fast bacteria has the properties of a protein of the alpha globulin classification. This protein is an enzyme which acts on spermine. Presumably, some product of the enzymatic reaction exerts a toxic effect on mammalian tubercle bacilli.