Immunity Acquired by Intoxication 103 



able success, for the prevention of bubonic plague, and A. E. Wright* 

 followed pretty much the same method for the prevention of typhoid 

 fever. 



In all these cases the immunity induced by the experimental 

 manipulations is specific in nature, and variable in intensity, ac- 

 cording to the method of treatment adopted and the thoroughness 

 with which it is carried out. 



2. Immunity Acquired by Intoxication. — Bacterio-toxins form a 

 miscellaneous group of active bodies of entirely different chemical 

 composition and physiologic activity. Some are toxalbumins, 

 some are enzymes, some are bacterio-proteins. The true nature of 

 the greater number of these bodies is unknown, but study of their 

 physiologic action has brought forth the important fact that their 

 behavior toward the body cells is in no way different from the 

 behavior of the same cells toward other chemical compounds of 

 similar constitution, and that nearly all physiologically active bodies 

 introduced into living organisms produce definite, though not 

 necessarily visible, reactions. 



Such reactions are now known as antigenic, and the substances 

 by which they are induced have been called by Deutschf antigens. 

 Since its introduction the precise meaning given the word by Deutsch 

 has been slightly changed. An antigen is any substance which 

 when injected into the body of a living organism is capable of pro- 

 ducing a chemicophysiologic reaction resulting in the appearance of 

 a neutralizing, precipitating, agglutinating, dissolving, or other- 

 wise antagonizing substance known as an antibody. 



The antigens are, so far as known, all colloidal substances. They 

 may be harmful or harmless, active or inert, living or dead, organized 

 or unorganized. The reactions are specific and the antibody has 

 specific affinity for that antigen alone by which its formation has • 

 been excited. 



All poisonous substances are not antigens, even though a certain 

 immunity — in the sense of habituation or tolerance — may follow 

 their repeated administration. One may become habituated or 

 tolerant to a certain quantity of merciury or arsenic, and to certain 

 alkaloids, such as morphin, caflfein, nicotin, cocain, etc., but he 

 does 'not react as to them as to antigens and no antibodies antago- 

 nistic to them are formed. To these various substances he really 

 acquires only a slight degree of tolerance; to the effects of injurious 

 antigens he may acquire an almost unlimited degree of immunity 

 through the formation of the antibodies. 



From remote antiquity it has been known that those who regularly 

 consume small quantities of poisons become irresponsive to their 

 action, and it is well known that Mithridates attempted this mode of 

 defending himself from his enemies. 



* Ibid., Jan. 30, 1897, i, p. 256. 



t Deutsch und Feistmantel, " Die Impfstoffe und Sera," 1903, Leipzig, Thieme. 



