1. The preparation and purification of paracasein was described and certain criteria for the absence of free enzyme provided for.

2. The solubility of purified paracasein in water at low temperature was studied, and found practically identical with the solubility of casein.

3. The capacity of paracasein to bind base was investigated by means of its solubility in NaOH at 5° and at 23° ± 2°C., and found to be distinctly different from that of casein.

4. At these two temperature levels paracasein had a 1.5 greater capacity to bind base than casein. The equivalent combining weights of paracasein and casein were found to stand each to the other, apapproximately, as 2 to 3.

5. This relationship suggested that the temperature coefficients of the solubility of paracasein and casein in NaOH are identical.

6. This evidence indicates that paracasein is a modification of casein, distinguishable by physicochemical means.

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