Artificial immunity against toxins 369 



nature of the intoxication, all doubt must give way before the case 

 described by Brieger 1 . One of his goats, well-immunised with tetanus 

 toxin, which, for months, had furnished a good serum and even an 

 antitetanus milk, after an injection, stronger than the preceding ones, 

 was seized with tetanic contractions. These, becoming general, 

 brought about the death of the animal with the symptoms of classic 

 tetanus. The blood, drawn off after death, exhibited strong antitoxic 

 power. 



As the result of these observations von Behring formulated the 

 theory of a hypersusceptibility acquired during immunisation. " Para- 

 doxical as it may appear," he writes 2 , "there can no longer exist 

 any doubt that horses which have acquired a high immunity as the 

 result of treatment with tetanus toxin, present a histogenic hyper- 

 susceptibility of the organs which react against the tetanus toxin." 

 In support of this thesis von Behring compares the effect produced 

 by this toxin on horses immunised with this same poison and on 

 normal horses treated with antitoxic serum from other horses. The 

 former, in spite of the fact that they contain in their blood 1 ,500 times [388] 

 more antitoxin than do the latter, are, nevertheless, less refractory 

 to tetanus toxin. This feeble resistance is due, in von Behring's 

 opinion, to the much greater susceptibility of the living elements in 

 the horses treated with repeated doses of the poison. 



Von Behring's theory of this form of acquired specific hyper- 

 susceptibility has been confirmed by several well-observed facts. 

 These show that, in the animal subjected to treatment by toxins, 

 phenomena of very diverse order are evolved simultaneously : on the 

 one hand, cell reactions which bring about the production of anti- 

 toxins ; on the other, an increase in the susceptibility of some of the 

 living elements to the specific poison. We are, however, justified 

 in asking if the great difference between the immunity of animals 

 treated with toxin, and that of others treated with antitoxic serum, 

 can be altogether attributed to this hypersusceptibility? 



Let us examine in a little more detail some examples of this 

 hypersusceptibility. We know that the guinea-pig is characterised 

 by its great natural susceptibility to the toxins of tetanus and diph- 

 theria. Small doses of these poisons are quite sufficient to produce 

 in it a fatal intoxication. But it is possible to diminish greatly this 



1 Ztschr.f. Hyg., Leipzig, 1895, Bd. xix, S. 109. 



2 "Allgemeine Therapie der Infectionskrankheiten," in Eulenburg u. Samuel's 

 "Lehrb. d. allg. Therapie," Berlin u. Wien, 1899, Bd. in. 



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