160 CHEMISTRY OF THE IMMUNITY REACTIONS 



ANTIGENS- 



This term includes those substances which, when 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.^ Concerning 

 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 anti- 

 gen, and, as yet, it has not been finally established that any colloids 

 other than proteins can act as antigens. The exception is the race- 

 mized protein of Dakin, which Ten Broeck^ found to be entirely 

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

 present in the egg albumin used in preparing it. Solubility is an es- 

 sential character for antigenic action, for proteins that have been coagu- 

 lated by heat lose their antigenic capacity, while proteins that are not 

 coagulated (e. gf., casein, ovomucoid) retain their antigenic properties 

 after boiling.^ A tj^pical incomplete protein, gelatin, is devoid of 

 antigenic power (Starin).^ The same is true of the protamines and 

 histones.'' Hemocyanin, however, is antigenic (Schmidt)."" 



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

 amino-acids and simple polypeptids can act as antigens, and even such 

 large complexes as the proteoses are antigenic to but a slight degree if 

 at all.* Whether the entire protein molecule, or onh' groups thereof, 

 determine the characteristics of the antigen, is not known, there being 

 evidence which can be interpreted in favor of either view, but Wells and 

 Osborne^ have submitted evidence which indicates that a single pure 

 protein can act with and engender more than one antibody; this is 

 supported by Klein's demonstration of the production of two distinct 

 antibodies by immunizing with casein.''' * 



There seems to be no very definite relation between the amount of 

 antigen injected and the amount of antibody produced." Neverthe- 

 less Herzfeld and Klinger'- have advanced the hypothesis that the 

 antibodies are really fragments of the antigen molecules which have 



^ See the Review on Antigens by E. P. Pick, Kolle and Wassermann's Handbuch 

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



' Attempts to influence the capacity to produce antibodies by modifying diet 

 have not produced striking results. (See Zilva, Biochem. Jour.. 1919 (13), 172.) 



* Jour. Biol. Chem., 1914 (17), 369; also Schmidt, Proc. Soc. Exp. Biol. Med., 

 1917 (14), 104; Kahn and McNeil." 



^ See Wells, Jour. Infect. Dis., 1908 (o), 449; Jour. Biol. Chem., 1916 (28), 11. 



" Jour. Infect. Dis., 1918 (23), 139; corroborated by Kahn and McNeil, Jour. 

 Immunol., 1918 (3), 277. 



' Wells, Zeit. Immunitiit., 1913 (19), 599; Schmidt, Jour. Infect. Dis., 1919 

 (2.5), 207. 



'"Proc. Soc. Biol. Chem., 1919 (14) Ixix; Jour. Biol. Chem., 1920 (41). 



' See Fink, ,Jour. Infect. Dis., 1919 (25), 97; full review on proteoses as antigens. 



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



'» Folia Microbiol. 1912 (1), 101. 



" See Tsen, .Jour. Med. lies., 1918 (37), 381. 



'2 Biochem. Zeit, 1918 (85), 1. 



