The Specific Gravity of Synthetic Solutions of Serum Albumin and Serum Globulin

Moore and Van Slyke (1) find the specific gravity of plasma to be a more useful measure of total plasma protein in nephritis than the refractive index, the physical property previously most widely employed in this connection. The effects of varying salt, glucose, and non-protein nitrogen contents presumably prevent accurate protein determinations by the specific gravity method, but are not sufficient to interfere with obtaining valuable practical results. With regard to the future application of the method, the question arises as to how nearly the albumin and globulin fractions exert equivalent influences upon the specific gravity of plasma, since, if these are not nearly the same, the indicated total protein content in any case will depend upon the albumin-globulin ratio. The first step in an answer to this question should be obtainable from the results of measurements of the specific gravities of synthetic solutions of serum albumin, serum globulin, and their mixtures, which have accordingly been carried out. Fresh beef blood was allowed to clot, and the globulin fraction precipitated from the resulting serum by half saturation with ammonium sulfate. The albumin was precipitated from the globulin filtrate by saturation with ammonium sulfate. Both fractions were then dialyzed in cellophane sacks until negligible tests for sulfate were obtained. During the dialysis and in subsequent procedures, the solutions were protected from bacterial action by the presence of crystals of thymol. Precipitated globulin was put back in solution by the addition of a minimum quantity of sodium chloride. Both solutions were adjusted to approximately 12 per cent protein content by evaporation in a current of warm air, and their total protein contents then determined by drying weighed portions to constant weight at 105’