THEORIES OF IMMUNITY. 



The explanation offered by Ehrlich of this loss 

 of toxic power with no loss of combining power 

 is this: he supposes that in the ultimate toxine 

 molecule there exist two chemical affinities (sets 

 of atom-groups), one of which has the power to 

 bind the molecule to a corresponding affinity in 

 the antitoxine molecule, and to which he gives 

 the name of 'haptophorous' 1 affinity; but he 

 supposes that there also exists another set of 

 atom-groups, which exert the toxic power of the 

 toxine molecule when the haptophorous group 

 has bound the molecule to another, and this he 

 calls the " toxophorous " affinity or atom-group. 

 In the case of the loss of toxicity observed in 

 toxine that has been kept for some time, he sup- 

 poses that it is this toxophorous group that has 

 been altered, whilst the haptophorous group has 

 remained unchanged. This supposition, if cor- 

 rect, would account for the condition seen — the 

 loss of toxic property, and the retention of the 

 combining property in as high a degree as it 

 existed at first. 



Applying this supposition to actual facts ob- 

 served, the action of the toxines in diphtheria 



47 



