On the Refractive Indices of Certain Proteins:

The change in the refractive indices of salt solutions which results from the addition of 1 per cent of the “pseudoglobulins” of blood serum has been measured by Reiss.l His pseudoglobulins were prepared by fractional precipitation with ammoniun sulphate and purified by prolonged dialysis. Fraction I (Pseudoglobulin I) was precipitated at 32-36 per cent saturation with ammonium sulphate, fraction II (Pseudoglobulin II) was precipitated at 36-39 per cent saturation. The change in the refractive index of the solvent due to the introduction of 1 per cent of the ‘(Pseudoglobulin I” was .00224, that due to the introduction of the (‘ Pseudoglobulin II” being .00230. Reiss adds that the difference between these determinations is not sufficient to constitute a basis for distinction between the two globulin-fractions, since it is not greater than that which might have arisen through experimental error. It appeared of some interest to ascertain whether the mode of preparation of the serum-globulin has any effect upon the change in the refractive index of a solvent which is brought about by its solution therein. There would appear to be at least, two globulins in serum, the one insoluble in distilled water, which is precipitated on dialysis of the serum or dilution and the subsequent addition of a weak acid; the other soluble in water, precipitable by saturation with magnesium sulphate after the removal of the insoluble