458 BACTERIOLOGICAL CHEMISTRY 



In the region of antibody excess the structure of the 

 framework would be represented as in Fig. 12, in which 

 only one valence of many of the antibody molecules 



X / \ / \ / \ / \ / 



• • e e « 



/ \ / \J\ /^\ / \ / \ 



Fig. 12. 

 is involved and the precipitate has a higher proportion of 

 antibody than it has in the equivalence zone. The 

 proportion of antibody may be so high that the complex 

 is soluble and give rise to the so-called " inhibition " or 

 " pro -zone." The formation of precipitates by the 

 interaction of multivalent haptens and antibodies is 

 accounted for on the same basis, whilst monovalent 

 haptens could not give rise to such a framework. Thus 

 OH R R R 



haptens such as R<^ ^OH or H0<(^ ^ < ( ^QH, 



OH R R 



where R represents diazotised arsanilic acid, 



— N=n/ X^sOgHa , give precipitates with anti- 

 serum prepared by injection into rabbits of diazotised 

 arsanilic acid coupled to protein. Haptens like H0<^ ^r, 

 containing only one determinant group, do not give pre- 

 cipitates although they combine with the antiserum. 



Boyd suggests that antigen-antibody precipitates do 

 not arise as the result of building up aggregates by the 

 framework process but that they result from the pre- 

 vention of the lyophilic polar groups of antibodies and 

 antigens from exerting their normal " solubilising " 

 function. The comparatively large antibody molecules 

 are visualised as l)eing lield closely together by the 

 antigen or liapten molecides in such a way that the 

 uncom])ined polar groups of the antibody are " occluded " 



