SIDE-CHAIN THEORY 



153 



different toxins on the remote chance that some one of these 

 may at some time or other come within the particular 

 sphere of action of one of those groups. Moreover, small 

 amounts of anti-bodies, such as antitoxin, bacteriolysin, 

 agglutinin, etc., are met with in normal untreated animals 

 and in man. While some have supposed that the small 

 amount of diphtheria antitoxin (equivalent to half a unit 



FIG. 26. Diagram to represent 

 the cell with its various com- 

 bining groups or side-chains. 

 (After Ehrlich.) 



FIG. 27. First stage in anti- 

 toxin formation. (Black = 

 toxin molecule. (After Ehr- 

 lich.) 



or so) present in human blood-serum is due to an infection 

 with the diphtheria bacillus (not necessarily an attack of 

 diphtheria), it seems more rational to suppose that this 

 antitoxin is due to a natural liberation of such side- chains 

 from the protoplasm and that artificial antitoxin pro- 

 duction is merely a very great stimulation of this natural 

 process. 



The toxin molecule, according to Ehrlich, possesses at 

 least two fixative atomic groups or side-chains. One 

 of these, the " haptophore group," conditions the union 

 of the toxin molecule with cell-protoplasm ; the other, 

 the " toxophore group," conditions its toxic action. 

 Similarly, in order that the cell may suffer the full effect 

 of the action of the toxin, it also must possess two receptive 



