ON SPECIFIC THERAPEUTICS. 9 



tion therefore necessary for such action is the 

 presence of two groups, whose chemical rela- 

 tionship is of the closest, and whose interaction 

 is therefore the condition of their union. This 

 axiom as to union is the basis of my side- chain 

 theory. 



Let us consider in the first place the action of 

 comparatively simple toxins, which differ in the 

 phenomena of intoxication to which they give 

 rise ; the action of the diphtheria-toxin, for 

 example, is absolutely different from that of the 

 tetanus-toxin. In the case of toxins, too, we are 

 justified in assuming a connection between their 

 chemical constitution and action, just as in the 

 case of poisons of known chemical constitution ; 

 this connection can in many cases be proved. 

 As an instance of this latter I would note the 

 fact that in the cocaine series it is the residue 

 of benzoyl which causes their anaesthesiophoric 

 character ; that the soporific action of certain 

 disulphons is entirely due to the presence in 

 them of ethyl groups ; and that the dulcific 

 character of certain sweet substances, e.g. t 

 phenetidin-urea, is due to a like group. In the 

 case of the toxins there is a difficulty in our 

 way, due to the fact that, up till now, they have 

 not lent themselves to chemical analysis ; but 



