THE DEFENSES OF THE BODY 301 



above) that the receptive molecules have been more or less 

 multiplied, according to the degree of immunity, through 

 bioplastic activity of similar, unimpaired atom-groups 

 surrounding those more directly influenced by the intoxicant 

 during the process of immunization; and that this excess 

 of such "receptors/' although physiologically useless, being 

 of no known service to normal function, circulates unchanged 

 in the blood, and serves, through specific combining affinity 

 for the poison against which the animal has been rendered 

 immune, to protect the normal tissues from its hurtful 

 action. 



According to the nature of the irritant from which the 

 animal has been immunized, the " receptor' ' is conceived 

 to be either of simple or complex construction, and its pro- 

 tective function to be performed in either a comparatively 

 simple and direct way, or in a more or less complicated and 

 roundabout manner. 



As a result of his studies of toxins, Ehrlich reached the 

 conclusion that they are composed of at least two function- 

 ally distinct atom-groups: the one, a "haptophore" group, 

 characterized by its combining tendencies; the other, a 

 "toxophore" group, distinguished for its intoxicating powers; 

 and that for the exhibition of its hurtful characteristics a 

 toxin molecule needs to be first anchored, so to speak, to 

 the susceptible tissue by the "haptophore" group, after 

 which its intoxicating characteristics are exhibited by the 

 "toxophore" group. He conceives the "receptors" to be 

 likewise provided with "haptophore" groups that pair with 

 the corresponding " haptophores" of the poison to which 

 the animal is susceptible or from which it has been immu- 

 nized. Where immunization has been induced against such 

 relatively simple substances as toxins, ferments, and certain 



