IMMUNITY 217 



mass-action of Guldberg and Waage, if one supposes a state 

 of unstable equilibrium to exist among the combinations.^ 



The combination toxin + antitoxin must therefore be dis- 

 sociable ; Arrhenius and Madsen are of the opinion that they 

 have demonstrated this by their experiments on the diffusion 

 of the mixture in a column of solidified gelatine and by their 

 distribution experiments {e.g., distribution of agglutinin between 

 bacteria and the immersing fluid). Many facts which led 

 Ehrlich to his hypothesis on the toxins are explained by 

 Arrhenius in terms of these dissociations, and in general by 

 the fact that antibodies and antigens have only a feeble affinity 

 for each other. 



To the diffusion experiments it has been urged in reply that 

 the dissociation only takes place because the mixture poured 

 on the gelatin has not had time to form the final combination ; 

 while to the hypothesis that a quantity of free toxin is present 

 in the mixture, it has been replied that if this were the case 

 antitoxin would never act in the body ; the body would fix 

 the free toxin, the toxin-antitoxin equilibrium would be dis- 

 turbed, a new quantity of toxin would be set free, and 

 so on. 



Physical chemists regard the dominant idea of Arrhenius's 

 theory with great reserve ; they doubt the justice of employing 

 the laws of chemical equilibrium and rates of reaction in 

 speculations as to the reactions which go on between bodies of 

 which nothing is known from the chemical point of view. 

 Nernst has verified the use made of the laws of reversible 

 actions, and he denies the possibility of applying to colloidal 

 substances laws established only for homogeneous liquids. 



This does not mean that there is anything odd in attempting 



' When a substance in solution of a molecular concentration m reacts 

 with another substance in solution in concentration «, the mass of the 

 substance formed by their combination is in a given time proportional to 

 the product mn. 



For example, when in a given volume 3 molecules of alcohol react with 

 2 molecules of acetic acid, the quantity uf acetic ether formed in a given 

 time is 3x2 =6; if $ molecules of alcohol react with 3 molecules of 

 acetic acid the quantity of acetic ether formed in the same time is expressed 

 L-y S X 3 = IS- 



