NEUTRALISATION OF TOXIN 157 



the toxophore groups have been destroyed while the 

 haptophore groups remain unaffected. It is the presence 

 of the haptophore group which conditions the union of 

 toxin with antitoxin. Thus, if toxin be injected into 

 blood containing antitoxin, the haptophore groups of 

 the toxin unite with the free receptor groups, i.e. with 

 the antitoxin (Fig. 32), and therefore the toxophore groups 

 cannot exert their influence 

 because the toxin is now 

 unable to unite with the pro- 

 toplasm, its haptophore or 

 binding groups being already 

 occupied. 



In a poisonous toxin, such 

 as diphtheria or tetanus toxin, 

 the toxophore group is more 

 readily destroyed than the FIG. 32. Neutralisation of toxin 

 haptophore group, and by ^~ h , in the "^ 

 heating a toxin for some 



time to 60-70 C. its toxicity is destroyed, but it still 

 retains an affinity for antitoxin. If some antitoxin be 

 mixed with such heated toxin it will be found that the 

 capacity of the former for neutralising active toxin is 

 much diminished in other words, although the toxophore 

 groups of the heated toxin have been destroyed, the 

 binding or haptophore groups still remain. Toxin which 

 has been kept for some time decreases in toxicity, but 

 retains the power of combining with antitoxin, again 

 showing that haptophore or binding groups are present 

 (such derivatives of toxin possessing haptophore groups 

 are termed " toxoids "). Wassermann and Bruck have 

 obtained presumptive evidence of the existence of the 

 second stage in antitoxin formation, viz. the increased 

 production of receptors by the cells. Using tetanus toxin 

 which had been kept for some time and had lost its 



