Abstract
The growth of Bacillus stearo-thermophilus was inhibited by raw or mildly heated milks; however, the growth of Bacillus subtilis was not inhibited under the same conditions. A microbiological assay for the determination of inhibitor concentrations was developed. After fractionation of the milk, the major portion of the total inhibitory activity remained with the acid-insoluble (pH 4.6) fraction, indicating that the milk component (s) which inhibits B. stearothermophilus is. or is associated with, the casein fraction.