INFECTION AND IMMUNITY 367 



tremely useful in enabling the student to think clearly 

 upon the genesis and operation of the antibodies, and 

 therefore has been exceedingly' popular for a decade or 

 more. 



The investigations began with a study of the chemical 

 constitution of the diphtheria toxin, and it is important 

 to remember that the experiments were made with toxic 

 antigens before other antigens and antibodies were well 

 known. Ehrlich found that the diphtheria toxin was 

 not stable, but lost its toxic properties with the lapse 

 of time. This did not, however, prevent it from com- 

 bining with the antibody in the usual proportions, so 

 that it seemed as though the molecules of the toxin were 

 possessed of dual qualities which might be described as 

 poisoning and combining, respectively. To the poi- 

 soning qualities he applied the term toxophores, to the 

 combining qualities, haptophores. In Ehrlich's imagina- 

 tion a toxin molecule (its chemical composition being 

 unknown and therefore impossible to represent by chem- 

 ical symbols) is pictured thus: 



Toxophore 

 groufr 8roup, t 



TZwwtt, Ce< 



FIG. 133. FIG. 134. 



He conceives that the toxin molecules attach them- 

 selves to the cell protoplasm by virtue of receptors or 

 hypothetical processes possessing adaptations to such 

 molecular combinations as are utilized by the cells in 

 their nutrition and function, and incidentally to the 



