166 CHEMISTRY OF THE IMMUXITY REACTIOXS 



ANTIGENS ■' 



This term includes those substances which, Avhen introduced into 

 the blood or tissues' of an animal, in proper amounts and under 

 suitable conditions, cause the generation and appearance in the blood 

 of specific antibodies capable of reacting with the antigen. Con- 

 cerning the chemistry of antigens we can say that all antigens, so 

 far as now known, are colloids. Furthermore, with one exception, 

 every known soluble, complete protein may act at least to some degree 

 as an antigen, and, as yet, it has not been finally established that any 

 colloids other than proteins can act as antigens. The exception is 

 the racemized protein of Dakin, which Ten Broeck -"^ found to be en- 

 tirely non-antigenic although soluble and possessed of all the amino- 

 acids present in the egg albumin used in preparing it. Solubility is 

 an essential character for antigenic action, for proteins that have been 

 coagulated by heat lose their antigenic capacity, while proteins that 

 are not coagulated (e. g., casein, ovomucoid) retain their antigenic 

 properties after boiling.-'' 



Of the cleavage products of proteins it is certain that none of the 

 amino-acids and simple polypeptids can act as antigens, and it is 

 not yet fully established that even such large complexes as the pro- 

 teoses are antigenic, although there is some evidence in favor of this 

 view. AYhether the entire protein molecule, or only groups thereof, 

 determine the characteristics of the antigen, is not known, there be- 

 ing evidence w^hich can be interpreted in favor of either view, but 

 TVells and Osborne ^ have submitted evidence which indicates that a 

 single protein molecule can act with and engender more than one 

 antibody; this is supported by Kliein's demonstration of the produc- 

 tion of two distinct antibodies by immunizing with casein.^'' 



It has been shown by Gay and Robertson,* moreover, that if the non- 

 antigenic cleavage products of casein are resynthesized by the re- 

 A^erse action of pepsin, into a protein resembling paranuclein, this 

 synthetic protein is capable of acting as an antigen. Protamins and 

 globin, they found, were not antigenic,^ although globin when com- 

 bined with casein forms a compound wliicli engenders an antibody that 

 gives complement fixation reactions witli globin. Schmidt also found 

 that protomain edestinate is antigenic for edestin and for itself, but 

 not for protamins, whereas a compound protein, both elements of 

 which were non-antigenic (globin-albumose), was not antigenic. °''- 



2 See the Tlevicw on Antifrens by E. P. Pick, Kolle ami Wassorinaiin's ITaiullnicli 

 d. path. Mikroorpanismcn, 1912 (1), G85. 



-2aJour. Biol. Chem., 1914 (17), 369. 

 2b See Wells, Jour. Infect. Dis., 1908 (5), 449; Jour. Biol. Clicm.. 1910 (28), 11. 



3 Jour. Infec. Dis., 1913 (12), 341. 

 -3a Folia Microbiol., 1912 (1), 101. 



, 4 Jour. Biol, f'lioni., 1912 (12), 233. 

 ■ 5 Jour. Exp. Mod.. 1912 (IG), 479: 1913 (17). 535. 

 5a Univ. of Calif. Puld., Pathol.. 1910 (2). l.-i7. Koviow and biblioirrajiliy on 

 specificity. 



