216 MICROBES AND TOXINS 



the haptophorous and toxophorous groups has been conceived, 

 and that in toxin the toxones and toxoids have been postu- 

 lated. But the complexity is also due to the necessity of 

 making the facts conform to the idea of the chemical nature 

 of these actions, and especially to the law of multiply which 

 demands that the same quantity of toxin should always be 

 neutralized by the same quantity of antitoxin. The theory 

 flatters itself also on its capacity to explain the specificity of 

 the antibodies ; for the complexity of the groups is supposed 

 to be sufficiently great to permit a haemolysin against goat 

 corpuscles to differ from a hsemolysin against rabbit corpuscles. 

 Even for the fairly numerous cases in which specificity is not 

 rigorous an explanation is forthcoming: different receptors 

 possess certain elements in common, and it is possible that a 

 serum which precipitates horse serum may also precipitate the 

 serum of the ass. 



The side-chain theory has been of great service ; it has, its 

 supporters say, a great " heuristic " value, /.., it has been the 

 means of discovering many interesting phenomena, and has led 

 Ehrlich on to his chemotherapeutic studies, in which he has 

 gained such magnificent successes. 



Nevertheless, it cannot be said that these fortunate results 

 prove the truth of the theory : the discovery of " 606," for 

 example, proves neither the existence of the side-chains nor the 

 truth of the chemical theory of immunity, 



Theory of Chemical Equilibria. Again to explain the 

 action of toxin and antitoxin, Arrhenius, Madsen and Walbum 

 have proposed another chemical theory. They criticize the 

 complexity of the theory of Ehrlich, they do not admit the com- 

 plex nature of the diphtheria toxin, and they attach great im- 

 portance to the experiment of Danysz-Dungern on partial 

 saturation. The facts can be explained by conceiving the 

 toxin + antitoxin reaction as a chemical interaction, not 

 between a strong acid and a strong base, but between a weak 

 acid and a weak base, for example, ammonia and boric acid. 

 The reaction toxin and antitoxin is comparable with those 

 reactions known as reversible and is governed by the law of 



