Catalase scores of fat and cell-free milk were 25 ± 9% of the total catalase scores of whole milk. Relatively more free catalase was present in mastitic than in normal milk. Addition of H2O2 caused death and disintegration of leucocytes and addition of surfactants increased the rate of death of leucocytes and rate of O2 release from H2O2. Disruption of milk leucocytes by insonation released catalase without appreciable loss of activity. From these results it was concluded that, in the catalase test the H2O2 caused death and disintegration of leucocytes, thus liberating catalase which released O2 from H2O2. Enzyme activity of beef liver catalase was greater in the presence of heat-labile whey proteins of milk than in buffer. Presence of more than 2 × 105/ml of high catalase producing bacteria in milk contributed significantly to the catalase score of the sample.

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Author notes

1Paper No. N.S. 459. Supported by a grant (EF-00370) from the Division of Environmental Engineering and Food Protection of the Department of Health, Education and Welfare, and by the Research Committee of the Graduate School from funds supplied by the Wisconsin Alumni Research Foundation. Published with the approval of the Director of the Wisconsin Agricultural Experiment Station.

2Present address–Endocrine Laboratories, Madison, Wis. 53701.

3Visiting Professor from the Agricultural Research Council, Institute for Research on Animal Diseases, Compton, England.