114 THE SIDE-CHAIN THEORY 



concluded that the peculiar relationship between the amount of agglu- 

 tinin present in the free state and that taken up by the bacteria 

 could be readily accounted for on the basis of the law of distribution, 

 and he developed for this particular case the equation 



(Quantity of bound agglutinin) 3 



(Quantity of free agglutinin)* ' = * < constaQt ) 



The figures actually observed in the experiment and those theo- 

 retically expected are, indeed, so nearly alike that it would seem 

 unnecessary to seek for any further explanation of the Eisenberg 

 phenomenon (see accompanying table). But even though we 

 admit that the manifest antigen-antibody reaction can thus be satis- 

 factorily accounted for on the basis of purely physical absorption, 

 this in itself does not preclude the possibility of a subsequent 

 chemical interaction between the two substances. 



No. of agglutinin No. of units absorbed according No. of units absorbed according 



units added. to observation. to calculation. 



2 2 1 . 98 



20 20 19.3 



40 40 37.9 



200 180 180.3 



400 340 347.1 



2000 1500 1522.0 



10000 6500 6110.0 



20000 11000 10840.0 



Formation of Antibodies. If now we pass on to a consideration of 

 the question how the introduction into the body of a given antigen 

 can lead to the formation of corresponding antibodies, we do so 

 upon the basis that, even though physical laws may be operative 

 during the interaction between the two classes of substances, actual 

 chemical union must invariably occur. This, indeed, constitutes 

 the very key-stone of Ehrlich's side-chain theory, a study of which 

 must now engage out attention. According to Ehrlich's doctrine, 

 we must look upon every cell, stereochemically speaking, as being 

 composed of a central molecular complex upon the integrity of 

 which the life and activity of the cell depends, and of a variable 

 number of subsidiary molecular groups which serve the purely vege- 

 tative functions of the cell. The former Ehrlich appropriately 

 designates as the " Leistungskern," or functional nucleus of the cell, 

 and the latter as the so-called " Setienketten" or side chains. 



