THEORIES OF THE PRECIPITIN REACTION.

Various theories for the precipitin reaction have been advanced for thirty odd years. The general feature of most of them is that univalent and bivalent antibody and multivalent antigen form large aggregates when there is an excess of neither antibody or antigen. In this region precipitates sometimes occur, presumably because the hydrophilic groups are, in these structures, masked. In this paper a probabilistic discussion is given of the more general model and formulae derived for the critical point and the antibody antigen ratio. It is assumed that large appregates of antigen and precipitation are associated.