450 BACTERIOLOGICAL CHEMISTRY 



nor with a pseiidoglol)iilin-aiit-ipseu*ioglobuIiii precipitate. 

 These authors suggested that the change in composition 

 of the precipitate with the change in proportion of antigen 

 and antibody in the reacting mixture might be due to the 

 formation of a series of compounds of the general formula 

 AniGn, due to the presence of several combining groups 

 in the antigen and antibody. 



Heidelberger and Kendall developed this idea further, 

 and applying the Law of Mass Action were able to give 

 a series of equations which could be used to predict the 

 behaviour of antigen-antibody mixtures over a wide 

 range of proportions. They used the nitrogen-free Type 

 III pneumococcus specific polysaccharide as hapten and 

 purified antibody preparations consisting of euglobulin 

 as the antibody. They allowed varying proportions of 

 the reagents to react, separated the precipitate by centri- 

 fugalisation and analysed it for nitrogen to determine the 

 amount of antibody it contained. They showed that the 

 addition of increasing amounts of the polysaccharide to a 

 constant amount of antibody caused progressive removal 

 of antibody from solution until the optimum proportion 

 (or, as they name it, the equivalence point) was reached, 

 when neither antibody (A) nor polysaccharide (S) could 

 be detected in solution. On further addition of S it was 

 taken up by the precipitate until the end of the zone of 

 precipitation was reached. Actually the equivalence point 

 was a zone due to a certain amount of dissociation of the 

 precipitate, giving traces of A and S in solution. The 

 extent of the zone depended on the particular specimen 

 of antiserum which was used and on such factors as tem- 

 perature, but it was fairly constant for any one system. 

 The zone may be approached from either the hapten excess 

 or the antibody excess side, giving limiting values. For 

 the Type III polysacchari de-antibody system the values 

 for the nitrogen : polysaccharide ratio were 13-5 for the 

 antibody excess side and 8-6 for the liapten excess end of 



