QUANTITATIVE STUDIES ON THE PRECIPITIN REACTION ANTIBODY PRODUCTION I RABBITS INJXCTED WITH AN Azo PROTEIN*

The antibody titer of a serum has usually been given in terms of the highest dilution at which it will agglutinate, hemolyze, or precipitate the antigen, in terms of the volume of toxin it will neutralize, in terms of the optimal proportion in which flocculation with antigen takes place, in terms of mouse protection-all relative and often inaccurate measures giving no idea whatsoever of the actual mass of antibody involved. The dilution methods, particularly, are subject to an error of 50 to 100 per cent in the decision as to which tube is the last positive one. For the quantitative measurement of precipitins one need no longer be dependent upon such methods. With the recognition of antibodies as mod&d serum globulins (1) and with the establishment by the writers of the conditions for their maximum precipitation (2) an absolute method for the estimation of precipitating antibodies has been worked out (3), based on the earlier use, by Wu and his coworkers (4), of the micro Rjeldahl method for the analysis of antigen-antibody precipitates. The first application of this method was in the standardization of Type I antipneumococcus horse sera (3), in which the writers, with Sia, showed a parallel between mouse protection and the maximum amount of specifically precipitable protein, a relation which was confirmed by Felton (5). A preliminary report was then made on the amounts of antibody produced following injection of a red azo