LATERAL CHAIN THEORY 55 



union occurs between the toxin and the anti-toxin, since, according 

 to the law of multiples, a definite amount of anti-toxin unites 

 with a definite amount of toxin. If ten times the amount of 

 anti-toxin is used it will exactly neutralize ten times the amount 

 of toxin, and the mixture becomes inert. Again, the union of 

 the two substances follows well-known chemical laws, whereby 

 chemical union takes place more rapidly in concentrated than in 

 dilute solutions, and when the solutions are warm. If the mixture 

 of toxin and anti-toxin is heated, it, instead of being neutral, 

 becomes toxic again. This toxicity can be neutralized again by 

 the addition of fresh unheated an ti- toxic serum (reactivation). 



The production of bacteriolysins, cytolysins, agglutinins, pre- 

 cipitins, and anti-toxins are manifestations of the activity of the 

 immunized organisms. To further understand this activity, 

 Ehrlich's side-chain theory of immunity must be comprehended. 

 This is known as the chemical theory. To understand it fully 

 some consideration must be given to the study of the toxin mole- 

 cule. Ehrlich believes that each molecule of toxin is made up of 

 two groups of atoms, constituting what is known in chemical 

 nomenclature as lateral chains. Many molecules are made up 

 of a central body and lateral chain of atoms which are free to 

 combine with other groups of atoms without disturbing the central 

 body. 



The benzol ring is very suitable for the demonstration of the 

 relationship of the side chain to the central body. 



H 

 I 



/ C \ 

 H C ^C H 



II I 



H ( 



H 



BENZOL. 



