THE SIDE CHAIN THEORY 117 



has actually called forth an increased production of new receptors of 

 the same order, so that there is now present in the nervous system 

 a larger number with which the toxin molecules can combine. The 

 same experiment also shows that even though the toxoid has called 

 forth such an increased production of receptors this was not followed 

 by their liberation; for, if this had occurred, the toxin molecules 

 would have met these in the circulation, union would have taken 

 place there and the animal would have remained alive. We are thus 

 forced to the conclusion that within certain limitations, antigens, of 

 the toxin type at least, can call forth antibody liberation providing 

 that the toxophoric group has not been entirely destroyed. 



As regards the question whether antibody production can be 

 effected only in those cells upon which the toxophoric group can 

 exert a deleterious effect, or whether the same result can be reached 

 with other cells, it is clear from the experiment cited above, to show 

 that the toxins are actually bound by those cells which are susceptible 

 to their toxic influence, that the antitoxins are also formed by these 

 cells. This is further supported by an experiment of Roemer. This 

 investigator rapidly immunized the right conjunctiva of a rabbit 

 with abrin and then killed the animal. If now the right conjunctiva 

 was triturated with a single fatal dose of abrin and the mixture 

 was injected into an animal, no deleterious result followed. If, 

 however, the same was done with the left conjunctiva the animal 

 died. Roemer accordingly concludes that in the right conjunctiva 

 locally formed antitoxin must have been present. 



While the evidence is thus quite conclusive that cells which are 

 susceptible to the toxic action of the toxin molecule can also produce 

 antitoxins, there are other facts to show that this can also occur in 

 non-sensitive cells. If, however, by any chance the sensitive cells 

 are the only ones which possess the necessary combining group for 

 the toxin, they will of necessity be the only ones from which anti- 

 toxin formation can proceed. We have seen already that in the 

 case of the guinea-pig the nerve tissue is the only tissue which can 

 exercise a detoxifying action. In the case of the rabbit, on the other 

 hand, such an effect can be produced not only by the cells of the 

 nervous system, but also by the liver and the spleen. If, moreover, 

 a guinea-pig is injected with tetanus toxin the fatal dose is the 

 same, no matter whether the poison is injected intracerebrally, 

 intravenously, or subcutaneously. In the rabbit the result is 



