CHAPTER VIII. 



ANTIGENS AND THE TECHNIC OF SERUM 

 REACTIONS. 



NATURE OF ANTIGENS AND ANTIBODIES. 

 AGGLUTININS AND PRECIPITINS. 

 LYSINS. 



Hemolysis and the Complement Fixa- 

 tion Reaction. 



AGGRESSINS. 



OPSONINS, TROPINS. BACTERIAL VAC- 

 CINES. 



NATURE OF ANTIGENS AND ANTIBODIES. 



THOSE substances which cause specific antibody formation when 

 they are introduced into the tissues or the body fluids of the host are 

 called antigens. Their chemistry is as yet unknown, but available 

 evidence would indicate that they are protein in nature and highly 

 organized chemically. Degradation products of proteins, as albu- 

 moses and peptones and carbohydrates and fats, are not ordinarily 

 antigenic, that is, they do not lead to antibody formation when they 

 are introduced into the animal body. 1 The antigenic properties of 

 lipoids are still a subject of controversy: lipoids appear to play a 

 prominent part in certain types of immunological reactions, but their 

 ability to stimulate specific antibody formation cannot be regarded 

 as proven at the present time. 2 



The function of antibodies as specific offensive weapons of the 

 host against alien organisms or their products has long been recog- 

 nized in bacteriology, and most important laboratory diagnostic 

 methods have been elaborated through a study of the reactions 

 between specific antigens and their respective antibodies. Antibodies 

 are soluble and are found in various concentrations in blood serum 

 derived from immunized animals. Many attempts have been made 

 to determine changes in the chemical composition or physical proper- 

 ties of immune sera from those of normal serum. Atkinson, 3 Gibson, 



1 The injection of carbohydrates and fats may, however, lead to specific enzyme 

 formation. See Rohmann, Antigene Wirkung der Kohlenhydrate, Deutsch. med. 

 Wchnschr., 1914, xl, 204. 



2 See Pick, Kolle, and Wassermann, Handbuch der pathogenen Mikroorganismen, 

 2d ed., Bd. I, for discussion of the chemistry of antigens. 



3 Jour. Exp. Med., 1899, iii, 649. 



