The presence in normal human γ-globulin of molecules with an S20,w = 19 S in addition to those with an S20,w = 7 S is again demonstrated. Antigenic differences between these molecules are shown by agar diffusion studies. Quantitative precipitin studies confirm these differences and demonstrate that the "7" and "19" components partially cross react and are antigenically related. The possibility is raised that the larger molecules are polymers of a smaller unit similar to 7 S γ-globulin but

more »

... in carbohydrate and that antigenic differences may be due to the higher carbohydrate content as well as differences in size and shape.