SUSCEPTIBILITY AND IMMUNITY. 271 



be established by the injection of certain other bacilli, or of ster- 

 ilized cultures of bacillus X." 



This corresponds with facts subsequently developed by Issaeff 

 (1894) in his* experiments with reference to immunity in guinea- 

 pigs against cholera cultures injected into the cavity of the abdomen. 

 He found that a certain degree of immunity was established by the 

 previous injection of blood-serum from normal individuals', and 'also 

 of various acids, alkalies, and neutral liquids. The immunity pro- 

 duced in this way was, . however, feeble and temporary, and could 

 not properly be considered as identical with that produced by inocula- 

 tions with attenuated cultures which give rise to a mild attack of a 

 specific disease. 



Cesaris-Demel and Orlandi have reported (1894) their success in 

 immunizing animals against infection by the typhoid bacillus by 

 means of sterilized cultures of Bacillus coli communis, and the 

 reverse. 



While this chapter relates especially to acquired immunity from 

 infectious diseases, and this immunity has been shown to depend, in 

 a number of these diseases at least, upon the development of anti- 

 toxins in the body of the immune animal, it may be worth while to 

 refer briefly, before closing, to some examples of acquired immunity 

 of a different order, We refer to the tolerance to extremes of heat 

 and cold which may be established by habitual exposure, and, more 

 especially, to the tolerance to narcotics and irritant poisons, which is 

 very remarkable and has never been explained in a satisfactory 

 manner. Samuel (1*92) has presented experimental evidence which 

 shows that the local inflammation which results from the application 

 of croton-oil to the ear of a rabbit does not occur when a second ap- 

 plication is made to the same ear after recovery from the effects of 

 the first. That a tolerance may be acquired to comparatively large 

 doses of arsenic is well known, and the tolerance which the victims 

 of drug habits acquire to enormous doses of narcotics is a matter of 

 daily observation. In the writer's paper on acquired immunity, pub- 

 lished in 1881, an attempt was made to account for acquired im- 

 munity in infectious diseases as analogous to the immunity to drugs 

 just referred to ; but the experimental evidence presented in the pres- 

 ent chapter shows that the analogy has no scientific foundation in 

 the absence of any evidence that there is an antitoxin of morphia, of 

 cocaine, of narcotin, etc., in the blood of the habitues of. these drugs. 



