The Molecular Weight of Specific Poly- Saccharides*

The question of the molecular weight of the specific polysaccharides is one of great importance for an understanding of the mechanism of immune reactions. It has been found that the precipitin reaction, for example, may be accounted for as a chemical combination of antigen (or haptene) with antibody globulin in proportions depending on the relative amounts of antigen (haptene) and antibody present (1, 2). More particularly, the writers have shown (1) that in the presence of a large excess of antibody (A) the relative proportion of Type III pneumococcus specific polysaccharide (8) in the precipitate is as 1: 120, and that the proportion increases to 1:60 at the “equilibrium point,” at which the amount of X has been increased to the extent that the excess begins to appear in the supernatant fluid. The magnitude of these ratios is such that treatment of the reaction on a stoichiometric basis, or on the basis of the mass law, as was attempted by the writers, would be reasonable only if the molecular weight (formula weight) of S III were small in comparison with that of antibody globulin. Otherwise the precipitin reaction would be characterized as a colloidal, surface phenomenon, difficult of exact physicochemical analysis. The assumption of a comparatively low formula weight for S appeared reasonable, especially as Dochez and Avery (3)) the discoverers of the soluble specific substance of pneumococcus, had been impressed with its ready diffusibility through the body and its passage through the kidney. Likewise, its haptene nature,