ON SPECIFIC THERAPEUTICS. 11 



plasm the " receptors." The relations between 

 the receptors and the haptophoric groups repre- 

 sent the conditions under which distribution takes 

 place. The toxic action can occur only when 

 receptors fitted to anchor the toxins are present. 



The existence of receptors can be proved 

 experimentally. For, if to a solution of toxin 

 there be added receptors suitable for anchoring 

 the toxin, the solution becomes non-poisonous ; 

 this " binding experiment " plays a great part 

 in the study of immunity, since Wassermann, 

 working on the basis of the conclusions to be 

 drawn from the side-chain theory, first showed 

 that those cells of the central nervous system, 

 which were known to be affected by the action 

 of tetanus-toxin, anchored the toxin. 



In order that the poisonous action may take 

 place, we must presume not only the presence 

 of receptors, but that they should be present in 

 positions favourable to the toxin action being 

 brought about. When both the receptors and 

 the organs sensitive to the action of the poison 

 are present, the conditions for infection are 

 naturally most favourable ; then distribution 

 takes place at once, the poison circulating until 

 it reaches the sensitive cell. The action of the 

 tetanus-toxin, in the case of the guinea-pig, is 



