FORMATION OF ANTIBODIES 123 



it is physically absorbed, and it still remains active for this very 

 reason and because it is not chemically bound. 



A further consequence of Ehrlich's side-chain theory would be the 

 inference that it should not be possible to call forth antibody produc- 

 tion by immunizing with exactly neutralized antigen-antibody mix- 

 tures, for in such instances the haptophoric group of the antigen is 

 supposedly in combination with the corresponding group of the anti- 

 body, and it should hence not be able to combine with any receptors 

 in the body of the injected animal. Here also the facts are in accord 

 with the demands of the theory. It is thus impossible to call forth 

 any antitoxin formation with accurately neutralized toxin-antitoxin 

 mixtures. It should be added, however, that in such experiments it 

 is absolutely essential to have no free toxon present beside the toxin. 



Toxons are poisonous bodies which may be present in the diphtheria 

 bacillus cultures together with the toxins, but they differ from these 

 in being less toxic. Like the toxins, however, they possess a hapto- 

 phoric group which is capable of combining with the true antitoxin 

 though the affinity of the toxon for the antitoxin is feebler than that 

 of the toxin. Since the toxon effect is not acute, but only develops 

 after a period of two weeks or longer, it is clear that apparent neu- 

 tralization of a toxic bouillon, as tested by the non-development of 

 acute symptoms, does not imply the absence of toxons; and as the 

 latter contain the same haptophoric group as the toxins it is clear 

 that a mixture of both, which is neutralized by antitoxin only so 

 far as the toxins go, can still call forth antitoxin production. If, 

 on the other hand, both toxins and toxons are neutralized, then, as 

 I have pointed out, no antibody formation will take place. 



Analogous experiments with cellular antigens and their corre- 

 sponding antibodies have led to corresponding results, though these 

 are not so striking, as in the case of the toxin-antitoxin mixtures. 

 This, however, cannot be surprising, if it is borne in mind that con- 

 ditions here are much more complex. We have pointed out before 

 that an apparent paradox results when a constant quantity of 

 bacteria is treated with increasing quantities of agglutinin (page 111), 

 but we have shown that this finds a ready explanation on the basis 

 of the existence of so-called partial agglutinins which are "tuned" 

 to different agglutinable molecules in the bacteria, and that as a 

 consequence the apparent binding power of bacteria for their agglu- 

 tinins may be perfectly colossal. Under such circumstances one 



