THE SIDE CHAIN THEORY 119 



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 neutrali- 

 zation 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 condi- 

 tions 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 106), 

 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 

 could hardly expect to throw out of action all the agglutinable groups 

 in a given quantity of bacteria by treating these with a corresponding 

 agglutinin, even in very large amount. But notwithstanding this 

 difficulty Neisser and Lubowski obtained some sera by immunizing 

 with such mixtures, which contained no agglutinins at all. This, 

 to be sure, was exceptional; but they could show, nevertheless, that 



