Interpretation of the Ouchterlony Precipitin Test

Under ordinary test conditions specific precipitates in the agar plate do not interfere with the free diffusion of unrelated antigens and antibodies. Identical antigens always give rise to fusion of their specific precipitates. Unrelated antigens may produce complete intersection, partial intersection or fusion of their specific precipitates, depending on the relative concentration of the two precipitin systems. Comparison of several heated, formalized and urea-treated proteins with untreated controls resulted in complete fusion of their specific precipitates. Further studies are desirable in order to elucidate the precipitate patterns yielded by cross-reacting immune systems.