THE PROTECTIVE SUBSTANCES OF THE BLOOD. 369 



bouillon still possesses the original neutralizing power but a weaker 

 toxic action. Hence toxic action on an animal arid combining power 

 for antitoxin must be two different functions, the former remaining 

 constant and the latter decreasing. 



If we regard these conditions from the chemical standpoint, we 

 shall see that they are most readily explained by assuming that the 

 toxin molecule produced by the diphtheria bacilli contains two dif- 

 ferent groups, of which one, termed the haptophore group, effects 

 the union with antitoxin, while the other, the toxophore group, 

 represents the actual cause of the toxicity. These two groups also 

 differ in their stability, for the toxophore group is very unstable 

 the haptophore group far more stable. Modified poisons in which 

 there has been a destruction of the toxophore group while the hap- 

 tophore group has been preserved, and which have therefore com- 

 pletely lost their toxic action, are called "toxoids." 



The presence of such toxoids fully explains the apparent devia- 

 tions from the Jaws of equivalence which are observed in neutralizing 

 tests with toxin and antitoxin. This furnishes new and, to my mind, 

 incontrovertible proof for the chemical view of the process of neutral- 

 ization. 



In diphtheria poison at least, for reasons into which I cannot 

 here enter, it seems that the affinity of the haptophore group of the 

 toxoid molecule for the antitoxin is exactly the same as that of the 

 unchanged toxin. This indicates that the two functionating groups 

 of the toxin molecule possess a certain degree of independence. I 

 have tried further by means of refined investigating methods, such 

 as partial neutralizations, to extend the views concerning the con- 

 stitution of the poison molecule. My observations, so far as the 

 facts are concerned, have been completely confirmed from various 

 sources. Mention should be made especially of the excellent study 

 ot Madsen on diphtheria toxin and tetanus toxin, and of the inter- 

 esting experiments recently published by Jacoby on ricin and its 

 toxoids. 



In studying the two groups of the poison molecule, we are con- 

 cerned not only with a satisfactory explanation for the process of 

 neutralization. The presence of these groups gives us an insight 

 both into the nature of the poisoning and the origin of the antitoxin. 



So far as this last point is concerned, two facts in particular 

 indicate that the haptophore group takes a leading part in the 

 immunity reaction in the organism, viz , (1) the observation that 



