376 BIOLOGY OF PNEUMOCOCCUS 



homologous immune horse serum, which led the authors to the con- 

 clusion that the reaction could be accounted for quantitatively by 

 assuming the chemical combination of the components in a bimo- 

 lecular reaction, followed by a series of competing bimolecular 

 reactions which depend on the relative proportions of the com- 

 ponents. From the data, Heidelberger and Kendall then developed 

 additional mathematical formulas representing the developments 

 in the mechanism of the precipitin reaction. As the authors re- 

 marked in their 1929 communication, "Of all the reactions of im- 

 munity the precipitin test is perhaps the most dramatic and strik- 

 ing; while other immune reactions are more delicate, the precipitin 

 test is among the most specific and least subject to errors and 

 technical difficulties" ; and "The isolation of bacterial polysac- 

 charides which precipitate antisera specifically and possess powers 

 of haptens has not only afforded one of the components of a pre- 

 cipitin reaction in a state of comparative purity, but has greatly 

 simplified the analytical problem." By these exact quantitative 

 methods, the precipitin reaction has conferred inestimable benefits 

 on the immunologist in understanding the nature of immunological 

 phenomena, such as the relations between antigen and antibody, 

 in judging the purity of antigen, and in estimating the antibody 

 content of antipneumococcic serum. 



The chemical study of capsular polysaccharides and pneumo- 

 coccal antibody is furnishing clues to the process which operate in 

 the union between type-specific antigen and homologous antibody. 

 By simple chemical experiments, Chow and Goebel 226 showed that 

 the immunological activity of pneumococcal antibody protein is 

 to a great extent dependent upon the presence of free amino 

 groups in the protein molecule. With the work of Landsteiner and 

 van der Scheer 782 " 3 in mind and reasoning from the results of the 

 study on synthetic antigens made by Avery and Goebel (1929), 44 

 Chow and Goebel assumed that in the case of the type-specific anti- 

 body of Pneumococcus the spatial arrangements of the polar 



