RECEPTORS 



155 



arid a defect is again created (Fig. 28). Once more the 

 cell responds, and a fresh series of receptors is developed 

 (Fig. 29). But by this continual stimulation, as it were, 

 the cell commences to form the particular receptors in 

 excess of that needed to repair the defect created, and ultimately 

 these receptors are reproduced in such numbers that 

 they no longer all remain attached to the cell but some be- 

 come free in the plasma (Fig. 30). 

 These receptor sidechains, detached 

 from the cell and floating free in 

 the blood-stream, constitute the anti- 

 toxin. This excessive production 

 of side-chains after stimulation by 

 repeated injections of toxin is not 

 a phenomenon confined to anti- 

 toxin formation, but is a general 

 physiological law enunciated by 

 Weigert ; as a result of repeated 

 stimulation, over-production or 

 hyper-compensation is the rule 

 and is met with in various 



pathological processes. Ehrlich has termed the diverse 

 free receptors which occur in the body fluids in various 

 circumstances " haptines." 



The existence of both haptophore and toxophore groups 

 in the toxin molecule is suggested by the following experi- 

 ments. Tetanus toxin injected into the blood-stream of 

 an animal rapidly disappears, within a few seconds of 

 the injection, and even if the animal be at once bled, 

 the blood withdrawn being replaced by fresh blood, 

 tetanus ensues, but not until after the lapse of an in- 

 cubation period of some hours. The tetanus toxin, 

 therefore, immediately becomes fixed or anchored to the 

 tissues of the central nervous system. Evidently the 

 toxin molecules enter at once into combination with the 



FIG. 30. Fourth stage in 

 antitoxin formation. 

 Side-chain, i.e. antitoxin, 

 free in the blood. (After 

 Ehrlich.) 



