HYPERSUSCEPTIBILITY 353 



ceptibility under the general term of allergy, which means altered 

 reaction. Under this heading he classifies, A, those forms of hyper- 

 susceptibility in which the inciting substance is, as far as we know 

 at the present time, non-antigenic, and, B, that form of allergy in 

 which the inciting substance is a known antigen. 



We ourselves would rather define these subdivisions as, A, those 

 forms of allergy in which the mechanism of the hypersusceptibility 

 cannot be shown to be due to an antigen-antibody union, and, B, those 

 forms in which an antigen-antibody union within the body can be 

 proved to be responsible. 



The difference is a slight one, but may, in the future, perhaps 

 become a fundamental one, for our recent studies on the tuberculin 

 reaction make us believe that the conception of the word "antigen" 

 will necessarily change in the course of the next few years of in- 

 vestigation. 



We do not see any particular purpose in altering the Doerr 

 classification to one suggested by Coca 2 in which the general term 

 * * hypersensitiveness ' ' is subdivided into true anaphylaxis and allergy, 

 the term "allergy" here being confined to the reactions in which 

 no true antigen-antibody reaction can be determined. In fact, we 

 believe that this would be harmful, in that Coca thereby implies 

 that there is a general identity of mechanism underlying the mani- 

 festations which he classifies together as "allergy," some of which 

 are certainly open to justified differences of opinion. 



We will first deal with those forms of hypersusceptibility in 

 which truly antigenic substances are involved, and, for this form, 

 we may reserve the term of True Anaphylaxis. 



Anaphylaxis. As early as 1893, Behring 3 and his pupils 4 had noticed 

 that animals, highly immunized against diphtheria toxin, with high antitoxin 

 content of the blood, would occasionally show marked susceptibility to injec- 

 tions of small doses of the toxin. 



The phenomena observed by them was interpreted as an increased tissue 

 susceptibility to the toxin, and Wassermann, reasoning on the basis of 

 Ehrlich's side-chain theory, formulated the conception that the increased 

 susceptibility was due to toxin receptors, increased in number by immuniza- 



2 Coca, Tice ; s System of Medicine, Vol. 3, 1920. 

 3 Behring, Deut. med. Woch., 1893. 



4 Knorr, Dissert., Marburg, 1895 ; Behring und Kitashina, Bert, klin, Woch., 

 1901, 



