258 RECEPTORS OF THE FIRST ORDER 



When a toxin is kept in solution for some time or when it 

 is heated above a certain temperature (different for each 

 toxin) it loses its poisonous character. It may be shown, 

 however, that it is still capable of uniting with antitoxin, 

 and preventing the latter from uniting with a fresh toxin. 

 This confirms the hypothesis that a toxin molecule has at 

 least two groups: A combining or hwptophore, and a poison- 

 ous or toxophore group. A toxin which has lost its poisonous 

 property, its toxophore group, is spoken of as a toxoid. The 

 theory of antitoxin formation is further supported by the 

 fact that the proper introduction of toxoid, the haptophore 

 group, and hence the real stimulus, can cause the production 

 of antitoxin to a certain extent at least.* 



The close relationship between toxins and enzymes has 

 already been pointed out. This is still further illustrated 

 by the fact that when enzymes are properly introduced into 

 the tissues of an animal there is formed in the animal an 

 antienzyme specific for the enzyme in question which can 

 prevent its action. The structure of enzymes, as composed 

 of a haptophore, or uniting, and a zymophore or digesting 

 (or other activity) group, is similar to that of toxins, and 

 enzymoids or enzymes which can combine with the substance 

 acted on but not affect it further, have been demonstrated . 



These free cell receptors, antitoxins or antienzymes, which 

 are produced in the body by the proper introduction of 

 toxins or enzymes, respectively, have the function of com- 

 bining with these bodies hut no other action. As w^as pointed 

 out above, this is sufficient to neutralize the toxin or enzyme 

 and prevent any injurious effect since they can unite with 

 nothing else. Since these receptors are the simplest type 

 which has been studied as yet, they are spoken of by Ehrlich 

 as receptors or haptins of the first order. Other antibodies 

 which are likewise free receptors of the first order and have the 

 function of combining only have been prepared and will be 

 referred to in their proper connection. They are mainly of 

 theoretical interest. 



Ehrlich did a large part of his work on toxins and anti- 

 toxins with ricin, the toxin of the castor-oil bean, abrin, 

 from the jequirity bean, rohin from the locust tree, and with 

 the toxins and antitoxins for diphtheria and tetanus. Anti- 



