a1 From the Institute of Physiology, University of Uppsala, Uppsala, Sweden
The quantitative theory for the interaction between antigen and antibody presented in the previous paper has been compared with some experimental precipitin reactions published in the literature. These reactions include Type VIII pneumococcus polysaccharide-homologous (horse) antibody, egg albumin-(rabbit) anti-egg albumin and diphtheria toxin-(horse) antitoxin.
1. The general course of the experimental precipitation curves (total amount of precipitate, amounts of precipitated antigen and antibody) corresponded well to the theoretical type curves. Hence it may be concluded that the precipitates may be composed of mixtures of compounds of the types AG, A2G, A3G, …, ANG in accordance with the law of mass action. In the cases with ‘inhibition zones’, however, AG, or ANG, or both (and perhaps several more compounds) retain the same solubility as the free antigen (G) and free antibody (A).
2. With regard to the location of the ‘equivalence zones’, experiment and theory also showed a satisfactory agreement.
3. A hypothesis on the velocity of flocculation in the precipitin reaction is presented and compared with some recent results. The relation between the immunological concepts ‘equivalence (neutral) point’, ‘optimum point’ and ‘maximum precipitation point’ is also discussed.
(Received January 03 1945)