Estimation of the Size of Antigens by Gel Diffusion Methods

Abstract

ANALYSIS of the pattern of precipitation lines formed when antigens and antibodies diffuse towards one another in an agar gel is established as a valuable qualitative technique in immunology. In the systems commonly used, diffusion occurs either in a tube¹ or in a flat sheet of gel². Several theoretical treatments of the tube-diffusion system have been presented³. In the latest, and most satisfactory, by Augustin et al. ⁴, a formula is given for calculation of the approximate diffusion coefficients of antigens from accurate measurements of the position of the precipitin lines at various intervals of time. Great accuracy is not claimed for the method, however, and it is difficult to apply when several antigens are present. Korngold and van Leeuwen⁵ have given a theoretical treatment for systems where diffusion occurs in a flat sheet, which enabled them to deduce that the precipitation line would be convex towards the well containing the reacting material with the greater diffusion constant. Although this conclusion is valid, the equations derived are not suitable for calculation of accurate diffusion coefficients because they depend on the assumption, which we have found to be invalid, that free diffusion continues after precipitation has begun.