Abstract
1. 1. The quantitative microprecipitin technique of Heidelberger and MacPherson has been employed in the analysis of factors influencing precipitation of ragweed extracts and rabbit antiragweed serum. 2. 2. Refrigeration for forty-eight hours carried the precipitation to completion. There was least avidity of ragweed extract for rabbit antiragweed antibody in the region of considerable antibody excess. 3. 3. Striking differences were noted for two ragweed extracts in the relation between their protein nitrogen content and the total nitrogen precipitated from a single rabbit serum. 4. 4. The precipitinogenic activity of ragweed extracts diminished progressively during storage in the frozen state. 5. 5. A few preliminary experiments described the effect of “blocking” antibody upon this precipitating system. Normal serums were found to posses some inhibitory activity but much less than that observed with sera from treated ragweed subjects. The degree of inhibition by normal serum was unaffected by altering the conditions of precipitation in a manner which increased the effect of serum from treated ragweed subjects. 6. 6. A given amount of serum containing “blocking” antibody appeared to “neutralize” a fixed amount of antigen independently of the antigen-antibody ratio of the precipitating mixture. 7. 7. The significance of these observations is discussed.
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