The Solubility of the Plasma Proteins I. Dependence on Salt and Plasma Concentrations in Concentrated Solutions of Potassium Phosphate*

Since Panum (1) in 1851 found that protein separated from serum on dilution and the addition of acid, the most widely used means of defining the plasma proteins has been by describing their solubility behavior. Between 1859 and 1902 the work of Denis (2), Hammarsten (3), Burckhardt (4), Marcus (5), Kauder (6), Pick (7), and others established the definitions of these proteins as commonly used today. These definitions are based on studies of the solubilities of so called protein fractions separated from plasma or serum by .repeated precipitations and re-solution under specified conditions. The terms fibrinogen, euglobulin, pseudoglobulin, and albumin, if strictly used, should, therefore, designate the proteins separated by such procedures. Between 1890 and 1905 various attempts were made to measure the concentration of the individual proteins of serum by so called single fractional precipitation; that is, by determinations carried out on precipitates or filtrates from the first precipitation at specified salt concentrations. In 1901 Pinkus (8) published a method for estimating the serum prot’eins by such fractional precipitation with sodium sulfate at 37”. His method assumed no overlapping of the precipitation