122 THE SIDE-CHAIN THEORY 



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 dif- 

 ferent. Intracerebral injection of tiny doses readily leads to fatal 

 tetanus, while much larger amounts can be administered sub- 

 cutaneously without causing a fatal result, particularly if the larger 

 nerve trunks in the district in which the injection is made are 

 previously cut. As abundant antitoxin formation then takes place 

 notwithstanding the fact that the access of the toxin to the brain 

 has been excluded so far as possible, the inference, of course, is 

 perfectly warrantable that the antitoxin in question is largely 

 produced by cells which are not susceptible to the toxic action 

 of the poison. 



The same point is also well illustrated in the case of the alligator. 

 This animal is not at all susceptible to the action of tetanus poison. 

 But notwithstanding this fact the toxin rapidly disappears from its 

 blood after injection, and in its place large amounts of antitoxin 

 appear. Were the toxin only physically stored away in the tissues, 

 but not chemically bound, then we should not expect antitoxin for- 

 mation, and the toxin should still be demonstrable in the tissues. 

 This is what actually happens in scorpions. Metschnikoff injected 

 such animals with a thousandfold quantity of the toxin as compared 

 with that which is necessary to kill mice. The animals in this case 

 were likewise not rendered ill and the toxin here also disappeared from 

 the blood. But on testing for the presence of antitoxin none could 

 be found, and even after months it could be shown that unchanged 

 toxin was present in the liver. The interpretation of these findings 

 upon the basis of Ehrlich's side-chain theory is very simple. Neither 

 the alligator nor the scorpion are rendered ill by the toxin, because 

 neither animal possesses cells that could be deleteriously influenced 

 by the toxin. The alligator, however, produces antitoxin, because 

 its cells are nevertheless able to enter into chemical union with 

 the toxin, and it is for this reason that the toxin disappears from 

 the circulation. The scorpion, on the other hand, has no cells at its 

 disposal which could unite chemically with the toxin and it can hence 

 produce no antitoxin. The poison here simply disappears because 



