ANTIGEN-AXTJBODY REACTIONS 451 



the zone, vntli a mean value corresponding to an equiva- 

 lence point of 10- 8. The ratio of nitrogen to polysaccharide 

 in the precipitates depended on the ratio of hapten and 

 antibody reacting and not on the absolute concentrations. 

 Tlie range of antibody to hapten ratios in the precipitates 

 was 40 : 1 at the antibody excess end and 5 : 1 at the 

 hapten excess end of the zone. The soluble compound 

 which was formed in the inhibition zone of hapten excess 

 was shown to contain one more molecule of polysaccharide 

 than the imm.ediately preceding precipitate. They sug- 

 gested that at the equivalence point a compound AS was 

 formed. In the region of antibody excess compounds 

 AgS, A3S, A4S to AmS were formed progressively depend- 

 ing on the relative excess of antibody. In the region of 

 hapten excess iVSg was formed as the insoluble precipitate, 

 which yielded AS3 as the soluble compound occurring in 

 the inhibition zone. It was found, however, that this 

 formulation would not fit the requirements of the Law of 

 Mass Action, and later they suggested that the precipita- 

 tion resulted from a series of bimolecular reactions. The 

 first stage they considered to be the formation of the 

 compound AS, 



A + S ^=i AS 



having a composition corresponding to the equivalence 

 point ratio of antibody to polysaccharide. Since both 

 hapten and antibody are multivalent with respect to each 

 other as a result of possessing a number of reactive 

 groups, made up of repeated units of aldobionic acid and 

 amino -acids respectively, the compound AS is capable of 

 combining with more antibody or polysaccharide, which- 

 ever is in excess in the solution. In the region of antibody 

 excess the following reactions can occur as a second 

 step : — 



AS+A ^-=^ AS. A. 

 AS+AS ^=i AS. AS. 



