154 A MANUAL OF BACTERIOLOGY 



groups or side-chains having a maximum affinity for the 

 haptophore and toxophore groups of the toxin ; these 

 may be termed the " receptor " and " toxophile " groups 

 respectively (see Fig. 31). The relationship of each 

 fixative group of the corresponding groups viz. that of 

 the toxin and that of the side-chain of the cell must be 

 most intimate, and analogous to the relations to each 



FIG. 28. Second stage in anti- FIG. 29. Third stage in anti- 

 toxin formation. (After Ehr- toxin formation. Side-chains 

 lich.) beginning to be produced in 



excess. (After Ehrlich.) 



other of a male and a female screw (Pasteur) or of a lock 

 and its key (E. Fisher). 



The genesis of antitoxin on the " side- chain theory " 

 takes place in the following manner : Toxin being intro- 

 duced, the haptophore groups of the toxin molecules unite 

 with the particular receptor side-chains of the proto- 

 plasm for which they have an affinity (Fig. 27). By this 

 combination the physiological activities of the cell are 

 interfered with, a defect is created, the cell is damaged 

 (it is only necessary to consider the case of one cell, or, 

 more strictly of one molecular group of the cell-protoplasm). 

 But through its recuperative powers the cell soon recovers 

 by the formation of new receptor side- chains to take the 

 place of those which have been put out of action. On 

 injecting more toxin, this combines with these new receptors 



