Changes were studied in the standard solubility curve of fresh serum proteins by alterations in pH, temperature, concentration of protein, and nature of the salt used for precipitation.

The principal factor affecting the precipitation of protein fractions was a change in temperature. In order to investigate the proteins in their original states low temperatures are necessary.

Protein fraction A is altered by a change in pH and with the use of (NH4)2SO4 as a precipitant, fraction B by a change in pH and temperature, and use of (NH4)2SO4, C by a change in temperature and concentration of the protein, and D by a change in temperature and pH.

The solubility of D is independent of the amount of protein in solution in high concentrations of salt.

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