28 BIOLOGICAL LECTURES. 



of daily observation. In the writer's paper on acquired immu- 

 nity, published in 1881, an attempt is made to account for 

 acquired immunity in infectious diseases as analogous to the 

 immunity to drugs just referred to. But it is evident that in 

 the present state of science the analogy is incomplete, and 

 possibly delusive, in the absence of any experimental evidence 

 of the presence of specific antitoxins in the blood of those who, 

 as a result of habit, tolerate excessive doses of morphia, cocaine, 

 narcotin, etc. 



