HMMOLYSINS. 19 



teria, sensitizing these to the action of the alexin 

 (complement). According to Ehrlich, however, the 

 process is not analogous to a staining process, 

 but follows definite laws of chemical combination, 

 there being, in fact, no affinity whatever between 

 the complement and the blood-cells or bacteria. 

 Furthermore, according to this authority, the com- 

 plement always acts only through the mediation 

 of the immune body, which possesses two combining 

 groups; one, the cytophile group, combining with 

 the cell and another, the complementophile group, 

 combining with the complement. Both observers 

 have devised a series of ingenious experiments to 

 support their views. But as these can interest 

 only the specialist, I shall omit their discussion 

 here. For such details the original articles may 

 be consulted. 



Ehrlich's Side-chain Theory. The results of the 

 experiments made by Ehrlich to determine the rela- 

 tion of immune body, complement, and cell to one 

 another served as a further support for his so- 

 called Side-chain Theory. This he had formulated 

 several years before in order to explain the pro- 

 duction of antitoxin and other specific anti-bodies. 

 Because of the great importance of this theory, 

 which laid the foundation for much of this work 

 and which to-day occupies an important place in 

 our literature, and also because it will serve to 

 make the following more readily comprehensible, 

 it will be well to devote a little time to its study. 



