SPECIFICITY OF IMMVyF h'FACTIOXS 171 



foreign proteins whicli tiic alimentary digestive apparatus has not 

 had the opportunity to destroy. This conception of the nature of im- 

 mune reactions to antigens has been especially advanced and in- 

 vestigated by Victor C. Vaughan ^^"^ and his co-workers, and l)y Kmil 

 Abderhalden, who has demonstrated in various ways an increased 

 proteolytic power in the blood of animals which have received pa- 

 renteral injections of foreign proteins.'"'' Thus, if the antiserum re- 

 acts on the specific protein within a dialyzing sac, the products of 

 proteolysis diffuse into the surrounding medium, where they can 

 be detected by simple chemical reactions. Also, changes in the spe- 

 cific rotation of the protein or peptid solution can be observed by 

 the polariscopic reading before and after the action of the antiserum. 

 A particularly important corroboration of Vaughan 's theory is fur- 

 nished by tlie behavior of the racemized i)rotein of Dakin. Although 

 soluble, this protein cannot be attacked by the digestive proteolytic 

 enzymes, presumably because of its altered configuration ; and it" is 

 non-antigenic, presumably because it cannot be attacked by the pro- 

 teases of the blood and tissues. Likewise it cannot be nietabolized, 

 w^hether fed or injected subcutaneously.^"^ Here we have good evi- 

 dence of the fundamental identity of the three processes, digestion, 

 metabolism, antigenic activity. 



As immunity reactions manifest themselves, however, there are many 

 steps in the process besides simple hydrolysis of proteins, even if 

 This be the ultimate goal of them all. 



SPECIFICITY OF IMMUNE REACTIONS 



The many attempts to explain the various reactions of immunity 

 solely on the basis of known physico-chemical properties of colloids 

 all flatten out when the striking, characteristic, and often extreme 

 specificity of these reactions is considered. Chemical explanations 

 are but little more satisfactory. In enzyme action we find many com- 

 parable examples of specificity, — but this does not help, as the enzymes 

 are as mysterious as the antibodies. But no proposed explanation of 

 any of the reactions incited by antigens can be of value if it fails to 

 take into account the specificity of the reactions. We lack the space 

 here to consider the many ideas and the items of evidence which have 

 been advanced concerning this all-important chemical problem, but 

 refer the reader to the excellent discussion by E. P. Pick-^^"* The main 

 facts at present available are the following: Specificity was at first 

 supposed to depend solely upon biological relationships, for it was 

 found easy to distinguish the serum of animals of unlike nature by 

 n cans of the precipitin and other reactions, but the more closely re- 



-6a See Vaiiglmn, "Protein Split Products," Pliiladelpliia, 1913. 

 3" Abderhalden, "Abwehrferniento dos tierisclicn Oriranismus," Perlin. 10] 3. 

 "a See Ten Broeck, Jour. Biol. Cliem., 1014 (17). 3(1!). 



3S Kolle and Wassermann's Ilandhuch d. path. ^Mikroor^ranismen, 1012 (1), 

 685 ; full bibliography. 



