444 bacterioloOtICal chemistry 



If, however, oiie-tliird of the toxin is added to the anti- 

 toxin, the mixture allowed to stand for some time, then 

 another third of the toxin added, and after a further 

 interval the last third of toxin added, the mixture is not 

 non-toxic, as would be expected, l)ut quite strongly toxic. 

 Ehrlich explained this by assuming that crude toxin 

 contained a non-toxic fraction, epitoxonoid, which com- 

 bined only slowly with the antitoxin. If toxin and 

 antitoxin were mixed rapidly all the antitoxin com.bined 

 with the toxin and none wath the epitoxonoid. When only 

 part of the toxin was added and sufficient time allowed, 

 part of the epitoxonoid combined with the excess of 

 antitoxin until finally, after adding all the toxin, an 

 excess of toxin remained corresponding to the quantity 

 of antitoxin which had combined with epitoxonoid. 



Other explanations than Ehrlich's of the toxin-anti- 

 toxin reactions have been proposed. Arrhenius and 

 Madsen, for instance, claimed that the reactions followed 

 the Law of Mass Action just as any ordinary chemical 

 reaction. Assuming that w^hen one molecule of toxin 

 and one molecule of antitoxin combine two molecules of 

 the toxin-antitoxin complex are formed, 



A+T r— ^ 2at, 



they carried out experiments in which the amount of free 

 toxin was measured after the addition of various amounts 

 of antitoxin. From the Law of Mass Action equation : — 



[T] [A] = k [at]^ 



they calculated the dissociation constant, k, to be 0-0093, 

 and used this value to calculate the a,moimts of free 

 toxin which should be present for different concentrations 

 of antitoxin. The agreement between the observed and 

 calculated values was very close, as may be seen from 

 Table 31 :— 



