ILEMOLYSINS AND ALLIED BODIES 



441 



To explain the production of this antitoxin, the side-chain 

 theory supposes that the protoplasm or biogen of the animal tissues 

 consists of a central nucleus or functionating centre (C in Fig. 21), 

 attached to which there are innumerable arms or side-chains which 

 are of various shapes at their free ends, all of them slightly 

 different (A A). These side-chains are concerned physiologically in 



FIG. 21. Receptors of First Order (Ehrlich's theory) ; 

 Mechanism of Antitoxin Formation. 



the absorption of food molecules, which must, therefore, be likewise 

 provided with side chains, some, or all of which, have mouldings 

 which fit on to some of the mouldings of the biogen side-chains. 

 It is only by becoming locked on to the functionating centre of 

 the cells, by means of side-chains, that the food molecule can be 

 incorporated with the protoplasm of the cell and the potential 

 energy which the food contains made available to the tissues. 



