6 EXPERIMENTAL RESEARCHES 



fundamental in itself, has opened to pharmaco- 

 logy and therapeutics this new field in which the 

 principle of distribution is exemplified in an 

 ideal manner : for antitoxins and antibacterial 

 substances are, so to speak, charmed bullets 

 which strike only those objects for whose 

 destruction they have been produced by the 

 organism. I call these substances monotropic ; 

 the monotropism of these antibodies is charac- 

 terised by the fact that they are bacteriotropic or 

 generally speaking aetiotropic, i.e., they are di- 

 rected against bacteria or against those products 

 of their metabolism (toxins) which cause disease. 

 The definition of monotropism is, therefore, here 

 overlapped by that of specificity, which, in the 

 language of the study of immunity, is the cha- 

 racteristic of monotropic action. As the cause 

 of this specificity we must note, in my opinion, 

 only the effect of chemical relations which exist 

 between the agents of infection, or their products, 

 and the antibodies. From the very beginning 

 my standpoint has been, that all those sub- 

 stances which have the power to bring about 

 the creation of antibodies, I mean the antigens, 

 must be distinguished, as a matter of princi- 

 ple, from the other pharmaco-dynamical and 

 poisonous substances. That distinction I con- 



