SUSCEPTIBILITY AND IMMUNITY. QTL 
be established by the injection of certain other bacilli, or of ster- 
alized 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 toa 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 (1892) 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 habitués of these drugs. 
