10 EXPERIMENTAL RESEARCHES 



in their case, too, it has been found to be a 

 fruitful heuristic principle to formulate for them 

 similar relations between their constitution and 

 their action. Thus I designate that group of 

 the toxin molecule which is the cause of its 

 peculiar poisonous action as its toxophoric 

 group ; but the presence of this toxophoric 

 group is not of itself sufficient to bring about 

 the poisonous action for whilst the guinea-pig 

 is exceedingly sensitive to the tetanus toxin, 

 the rabbit possesses a relative immunity. The 

 cause of such difference we must therefore 

 attribute to the distribution or localisation of 

 the toxin. 



When the poison and the organs sensitive to 

 it do not come in contact, or when sensitiveness 

 of the organs does not exist, the action remains 

 absent. 



If we assume those peculiarities of the toxins 

 which cause their distribution to be localised in 

 a special group of the toxin molecule, and the 

 power of the organs and tissues to react with 

 the toxin to be localised in special atom groups 

 of the protoplasm, we arrive at the basis of my 

 side-chain theory. The distributive group of 

 the toxins I call the " haptophoric group," and 

 the corresponding chemical organs of the proto- 



