212 IMMTJNOLOGY 



the immune serum was more concentrated, they found that while 

 the same amount of bacteria actually adsorbed more agglutinin 

 than from the higher dilutions, yet the amount adsorbed was a 

 smaller percentage of the total amount present than in the latter. 



Effect of Fractional Addition of Antigen. — In 1905, Craw 

 showed that the way bacteria were added to immune serum in- 

 fluenced the amount of agglutinin adsorbed He found that if tlie 

 bacteria w^ere added all at once to the immune serum they adsorbed 

 more agglutinin than if added in fractional amounts with appre- 

 ciable time intervals between. This is similar to tlie Danysz phe- 

 nomenon where more toxin is neutralized by a given amount of 

 antitoxin added all at once than when added in fractional amounts 

 with some time intervening. Bordet's experiment of dye adsorp- 

 tion with filter paper illiLstrates this. 



Bordet's Experiment Explaining Danysz Phenomenon. — If a 

 dilute solution of a dye is prepared and a definite sized square of 

 filter paper is added, in small pieces at considerable time intervals, 

 the first pieces added will be intensely dyed while the last added 

 may not be colored at all. These results suggest that the adsorp- 

 tion of agglutinin by bacteria is in accordance with the law of 

 adsorption. It appears that the union does not follow any law of 

 simple proportions. 



Heidelberger and Kendall's Theory of Reaction Mecha- 

 nism. — Since it is thought that the mechanism involved in the 

 formation of immune precipitates is identical with the one involved 

 in the agglutination of bacteria by immune serum, the recent 

 theory of Heidelberger and Kendall* (1935, 1937) relative to the 

 mechanism involved in a bacterial precipitin reaction is of interest. 

 In the summary of their paper (1935) they say that ''the pre- 

 cipitin reaction between the specific polysaccharide of Type III 

 pneumococcus and homologous antibody found in the horse can be 

 accounted for quantitatively by assuming the chemical combination 

 of the components in a bimolecular reaction, followed by a series 

 of competing bimolecular reactions which depend upon the relative 

 proportions of the components. These reactions would lead to the 

 formation of larger and larger aggregates until precipitation ulti- 

 mately occurred. The mathematical formulation of this theory on 



♦Heidelberger and Kendall: J. Exper. Med. 61: 563, 1935. 



