1. Clean milk has been “flash” pasteurised at 165°F. Portions of the same raw milk have been treated with small amounts respectively of starter culture and lactic acid, so as to raise the acidity, before being similarly pasteurised.

2. Comparison of the whey obtained by rennetting the three raw portions has shown that those from the acidified milk contained more soluble protein than the original.

3. The differences between the raw and pasteurised milk in their coagulation time with rennin have been found to be proportionately much greater in the acidified portions.

4. These differences in coagulation time have been shown to be correlated with decreases in the amount of soluble protein found in. the whey separated from the coagulum.

5. These experimental results, together with those of other investigators, have been made the basis of a suggestion that the decreased coagulability of heated milk with rennin is partly due to flocculation of soluble milk protein upon the casein micelles.