112 PHYSICAL CHEMISTRY IN MEDICINE. 



there exist a large number of valuable quantitative 

 investigations, of which must be mentioned in particular 

 the fundamental work of EHRLICH on diphtheria toxin. 



I may perhaps be allowed, before entering into details, 

 to touch upon those few leading points which render 

 possible a simpler and more satisfactory conception of 

 the relation of toxin to antitoxin than has until now 

 been possible. Two assumptions suffice, both of which 

 rest upon a fully established experimental basis and are 

 generally accepted without contradiction: the colloidal 

 constitution of toxins and antitoxins, and their ability 

 to neutralize each other. Through these suppositions 

 is rendered possible the extension to the dark relations 

 existing between toxin and antitoxin of our advanced 

 insight into the process of colloidal precipitation. As an 

 actual matter of fact, we are dealing in both cases with a 

 neutralization of colloids, only the criterion which exists to 

 show that such a neutralization has occurred is different in 

 the two cases. For in the first case this consists in the 

 production of macroscopically visible aggregates, in the 

 second in the formation of non-poisonous ones. The 

 similarity between the general laws governing the two 

 sets of phenomena is, in truth, striking. 



It is a well-known fact, for example, that especially diph- 

 theria toxin when kept for longer periods of time under- 

 goes changes which are attributed to the formation of 

 various complexes from the originally simple toxin. An 

 analogous phenomenon is counted among the first-observed 

 and best-known facts of colloids in general. It is de- 

 pendent upon the presence of neutralizing impurities 

 which are in the course of time able to render manifest 

 their effect in the production of aggregates. The more 



