116 THE SIDE CHAIN THEORY 



with the botulismus toxin, which, like the tetanus toxin, possesses 

 a specific affinity for the nervous system, and we have already seen 

 that it is possible to remove hemolytic and bacteriolytic amboceptors 

 from the respective sera by mixing these with their corresponding 

 antigens. 



The next question which Ehrlich's theory would suggest has 

 reference to the experimental basis for the idea that the antibodies 

 are actually formed by the cells which possess suitable receptors for 

 the various antigens. Two possibilities present themselves in this 

 connection. We can conceive, on the one hand, that the antibodies 

 might be formed only by those cells whose functional nucleus can be 

 deleteriously influenced by the antigen, while on the other hand, the 

 possibility exists that any cell may produce antibodies to a given 

 antigen, providing only that it possesses a haptophoric group which 

 is capable of uniting with the antigen. Investigations in this direc- 

 tion have led to the conclusion that a mere union between antigen 

 and cell receptor is not always sufficient to call forth antibody libera- 

 tion, but that a special " Bindungsreiz," or stimulus, must also be 

 operative. Bruck thus found that on immunizing guinea-pigs with 

 two separate solutions of tetanus toxin which were several years old, 

 and of which one was still slightly toxic, while the other had lost its 

 toxicity altogether, antitoxin production could only be elicited with 

 the first. With the non-toxic specimen this was impossible, even 

 though it could be shown that this still had the power of binding 

 antitoxin, which means, of course, that its haptophoric group was 

 still intact. 



Bruck then argued as follows: If the nerve cell receptors of the 

 animal that has been treated with the non-toxic product, i. e., with 

 so-called toxoid, actually combine with this, then the subsequent 

 injection of a dose of active toxin of such amount as would be just 

 sufficient to cause death in a normal control, should now prove non- 

 fatal. As a matter of fact this is exactly what occurs, if the injection 

 of the toxin follows that of the toxoid immediately. If, on the other 

 hand, an interval of twenty-four hours is allowed to elapse between 

 the first and the second injection the latter will prove fatal, and it 

 may further be shown that after such an interval a dose which would 

 be subfatal for the control is now fatal for the toxoid animal. 



The interpretation, of course, is that the toxoid which was first 

 injected has not only combined with the nerve cell receptors, but 



