Artificial immunity against toxins 381 



Ehrlich^ has formulated another hypothesis to explain not only 

 this specificity but the origin of antitoxins in general. This is the [400] 

 ingenious hypothesis of side-chains or of receptors, which has already 

 been considered in other chapters of this work. It is now for the 

 first time brought forward in relation to the antitoxins properly 

 so-called, that is to say substances capable of preventing intoxication 

 by microbial toxins. In order to make his hypothesis as clear as 

 possible Ehrlich begins by explaining its bearing on the concrete 

 example of tetanus antitoxin. " When we introduce into an animal a 

 small quantity of tetanus toxin, it is easy to obtain exact proof that 

 it is quickly fixed by the central nervous system, probably by the 

 motor cells of the ganglia; that the central nervous system more 

 than any other organ attracts the tetanus toxin and retains its toxic 

 molecules very firmly." There we have the side-chains of the proto- 

 plasm fulfilling this role and subjecting the living protoplasm to the 

 prolonged action of the poison. Once it is combined, the side-chain 

 becomes incapable of fulfilling its normal function, and there is 

 induced on the part of the living elements the production of new 

 chains of a similar character. Following the law that the reaction 

 is stronger than the action, there is an over-production of these 

 side-chains which finally so embarrass the cell which has developed 

 them that they are excreted by it into the blood plasma. Once 

 expelled into this plasma, they continue to manifest their affinity 

 for the tetanus toxin, an affinity which must be even greater in 

 the case where the chains are found in the blood than when they 

 were connected with the cell. Owing to this affinity, these chains, 

 now in the blood, fix the tetanus poison introduced into the animal 

 and prevent it from reaching the susceptible nerve elements. Anti- 

 toxins, according to this hypothesis are, therefore, nothing but over- 

 plus side-chains poured into the body fluids. Ehrlich extends his 

 theory to a whole series of bodies capable of causing the formation 

 of antitoxins and antidiastases. "It is probable," he says, "that all 

 analogous bodies can only become toxic to the animal on condition 

 that the animal is capable of fixing their toxophore groups in certain 

 of the organs that are important for its life " (p. 17). 



According to this theory tetanus antitoxin must pre-exist in the 

 central nervous system of the normal animal In the immunised 

 animal, the side-chains must be reproduced in very great quantity 



1 "Die Werthbemessung des Diphtherieheilsenims " (iE'/iw. Jahrh., Berlin, 1897, 

 Bd. vi), SS. 13—17 of reprint. 



