THE TOXONE EFFECT 163 



equilibrium, a fraction of toxin and also of antitoxin 

 remains free, this fraction of toxin producing the " toxone 

 effect " (see p. 165). If equivalent quantities of acetic 

 acid and alcohol are mixed, the reaction is never complete ; 

 the acid and alcohol never entirely disappear, because the 

 water formed reacts with the ethyl acetate, re-converting 

 it into acid and alcohol. Such a reaction is termed rever- 

 sible, and this particular case could be thus represented : 



CH.COOH + CH.OHCH.COOCH H0. 



Bordet has suggested that the fixation of toxin by 

 antitoxin is an adsorption phenomenon, similar to the 

 fixation of a dye by a tissue. 



These hypotheses may now be examined more in detail. 

 Ehrlich's experiments l on diphtheria toxin seemed to 

 show that the neutralisation of toxin by antitoxin follows 

 the laws of simple chemical combinations, such as the 

 neutralisation of a strong base (NaOH) by a strong acid 

 (HC1). If so, it would be expected that antitoxin would 

 neutralise proportionate amounts of toxin ; but this is 

 not so, and Ehrlich was forced to the conclusion that toxin 

 is a complex mixture of proto-, deutero-, and trito- toxin, 

 and toxone, with different toxicities and different avidities 

 for antitoxin. Moreover, when toxin is kept it decreases 

 in toxicity, though still retaining much of its avidity for 

 antitoxin. Ehrlich assumed, therefore, that the toxin 

 becomes transformed into substances termed toxoids, 

 which are non-toxic but retain their affinity for antitoxin 

 (see also section on the standardisation of diphtheria anti- 

 toxin). This he explained as due to destruction of the 

 unstable toxophore groups, with the retention of the 

 more stable haptophore groups. That the neutralisation 

 of toxin by antitoxin is due to some sort of union between 



1 l-'w Trans. Jcnncr Inst. Prcv. Mcd., vol. ii, p. 1 ; Croonian Led., 

 Roy. tioc. Lond., 1900 ; and p. 293. 



