Immunity Acquired by Intoxication 115 



able success for preventing the disease. Later* he applied 

 the same method, also with considerable success, for the pre- 

 vention of bubonic plague, and A. E. Wright f followed pretty 

 much the same method for the prevention of typhoid fever. 



In all these cases the immunity induced by the'experimen- 

 tal manipulations is specific in nature, and variable in inten- 

 sity, according to the method of treatment adopted and the 

 thoroughness with which it is carried out. This variability 

 in the results attained will be much better understood after 

 the subject of immunization against toxins has been discussed. 



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 bac- 

 terio-proteins. The true nature of the greater number 

 of these bodies is unknown, but study of their physio- 

 logic 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 sub- 

 stances by which they are induced have been called by 

 Deutsch antigens. I Since its introduction the precise 

 meaning given the word by Deutsch has been slightly 

 changed. As now defined, an antigen is any protein sub- 

 stance which when injected into the body of a living organism 

 is capable of producing a chemicophysiologic reaction re- 

 sulting in the appearance of a self-neutralizing, self-precipi- 

 tating, self-agglutinating, self-dissolving, or otherwise self- 

 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 



* "Brit. Med. Jour.," 1895, n, p. 1541. 

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



J Deutsch and Feistmantel, "Die Impfstoffe und Sera," 1903, Leip- 

 zig, Thieme. 



