CHAPTER VII 



CHEMISTRY OF THE IMMUNITY REACTIONS— ANTIGENS, 

 SPECIFICITY, ANTITOXINS, AGGLUTININS, PRECIPI- 

 TINS, OPSONINS, AND RELATED SUBJECTS 



Although immunitj^ was first investigated in relation to bacterial 

 infection, it was soon learned that the reactions by which the animal 

 body defends itself against bacteria have not been developed as 

 specific means of defense against bacteria alone, but are reactions 

 against foreign substances of similar chemical nature, whether bac- 

 terial, animal, vegetable or artificially synthetic in origin. Further- 

 more, these reactions are chemical reactions, and the problems of 

 immunity are chemical problems, although as yet most of the react- 

 ing substances are not accessible to chemical investigation. In this 

 place, where our concern is with the chemical aspects of pathological 

 processes, the subject of immunity will be discussed only from the 

 standpoint of the chemistry of the processes and substances involved, 

 leaving to other works the clinical and bacteriological aspects of the 

 subject.' 



The reactions of immunity are, we find, reactions to chemical sub- 

 stances entering the body from without, or abnormally developed 

 within the body by invading organisms or by changes in the chemi- 

 cal processes of the body. Furthermore, there seems to be an essential 

 difference between the reactions incited by simple chemical compounds 

 to which the animal body can develop a certain degree of resistance 

 (such as morphine, alcohol, and arsenic), and the reactions against 

 more complex substances such as bacterial toxins, foreign proteins, 

 venoms, etc. The complex substances of the latter group incite 

 reactions which are to a greater or less degree specific, and usually 

 very highly augment the defense of the body against the foreign sub- 

 stances; with the simple poisons the reactions are largely or altogether 

 non-specific, and the resulting resistance is relatively slight. Sub- 

 stances of the first class we refer to as antigens. 



' Especially to be recommended for a discussion of the scientific problems of 

 immunology is Zinsser's "Infection and Resistance," Macmillan, New York, 1914; 

 and for methods and applications see Kolmer's "Infection, Immunity and Specific 

 Therapy," W. B. Saunders, Philadelphia, 1918. Also see Kolle and Wassermann, 

 "Handbuch der path. Mikroorganismen;" Weichardt " Jahresbericht der Immuni- 

 tatsforschung." 



159 



