CHAPTER XXVII. 

 RECEPTORS OF THE FIRST ORDER. 



ANTITOXINS -ANTIENZYMES. 



The general characteristics of toxins have been described 

 (Chapter XII). It has been stated that they are more or 

 less specific in their action on cells. In order to affect a cell 

 it is evident that a toxin must enter into chemical combina- 

 tion with it. This implies that the toxin molecule possesses 

 a chemical group which can combine with a receptor of the 

 cell. This group is called the haptophore or combining 

 group. The toxic or injurious portion of the toxin molecule 

 is spoken of as the toxophore group. When a toxin is intro- 

 duced into the body its haptophore group combines with 

 suitable receptors in different cells of the body. If not 

 too much of the toxin is given, instead of injuring, it acts as 

 a chemical stimulus to the cell in the manner already de- 

 scribed. The cell in response produces more of the specific 

 thing, which in this instance is more receptors which can 

 combine with the toxin, i. e., with its haptophore group. 

 If the stimulus is kept up, more and more of these receptors 

 .are produced until an excess for the cell accumulates, which 

 excess is excreted from the individual cell and becomes free 

 in the blood. These free receptors have, of course, the 

 capacity to combine with toxin through its haptophore 

 group. When the toxin is combined with these free receptors, 

 it can not combine with any other receptors, e. g., those in 

 another cell and hence cannot injure another cell. These 

 free receptors constitute, in this case, antitoxin, so-called 

 because they can combine with toxin and hence neutralize 

 it. Antitoxins are specific— that is, an antitoxin which will 

 combine with the toxin of Clostridium tetani will not com- 

 bine with that of Corynebacterium diphtherioe, or of Clostri- 

 dium hotulinum, or of any other toxin, vegetable or animal. 

 17 ( 257 ) 



