94 Immunity 



Wright* followed pretty much the same method for the 

 prevention of typhoid fever and thought that much success 

 was achieved, though others were not convinced of its 

 benefit. 



In all these cases the immunity induced by the experimen- 

 tal manipulations was specific in nature, and variable in 

 intensity according to the method of treatment adopted 

 and thoroughness with which it was carried out. This vari- 

 ability in the results attained will be much better under- 

 stood 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 dif- 

 ferent chemical composition and physiological activity. 

 Some are toxalbumins, some are enzymes, some are 

 bacterio-proteids. The true nature of the greater number 

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

 logical 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 bodies 

 produce definite, though not necessarily visible reactions. 



Some of the facts that bear upon immunity have long been 

 known though only recently correlated with it. Thus from 

 remote antiquity it has been known that those who regularly 

 consumed small quantities of poisons become irresponsive 

 to their action, and it is well known that Mithridates adopted 

 this mode of defending himself from his enemies. The im- 

 munity of opium and arsenic eaters, and the pleasurable 

 instead of poisonous effects of tobacco, are too well known 

 to require further mention. 



It was, however, only by beginning with the metabolic 

 products of bacteria, studying their activities, and comparing 

 them with other toxic and active substances that the present 

 state of knowledge has been attained. 



The work seems to have been begun by Chauveau, f who 

 believed that the immunity conferred by bacteria was due 

 to the presence of their soluble products, but the first direct 

 demonstration was given by Salmon and Smith, J who, as 



* " Brit. Med. Jour.," Jan. 30, 1897, p. 256. 

 f'Ann. de 1'Inst. Pasteur," 1888, 2. 

 t " Centralbl. f. Bakt," etc., n, No. 18. 



