The Relative Precipitating Capacity of Certain Salts When Applied to Blood Serum or Plasma and the Influence of the Cation in the Precipitation of Proteins.* by Paul

Evidence has been presented (1) indicating the occurrence of critical zones in the precipitation of the proteins of blood, Cpon the addition of increasing amounts of sodium sulfate at these zones there is not a marked increase in the quantity of protein precipitated for a given increase in salt concentration. The eones occur in the neighborhood of the following concentrations of sodium sulfate at 37°C.: 10.6 per cent (2), 14.2 per cent, 17.7 per cent, 21.5 per cent, or expressed in volume-molar concentrations, 0.75, 1.00, 1.25, and 1.50 molar, respectively. Comparison with certain existing procedures for separating proteins has shown that (a) the 0.75 molar solution precipitates the same amount of protein from plasma as that obtained by the addition of calcium chloride to oxalated plasma (2) ; (5) the 1.00 molar solution precip itates essentially the same amount of protein as that obtained by dilution and acidificat.ion of serum or plasma with CO* (1) ; (c) the 1.25 molar solution does not produce an appreciable precipitate in new-born calf blood, but does give a precipitate in adult blood or in the serum of the new-born calf within a few hours after the absorption of the proteins of colostrum or of blood (3) ; (cl) the 1.50 molar solution gives results which approximate the results obtained with saturated magnesium sulfate or one-half saturated ammonium sulfate (1). If we accept the quantity of