128 A STUDY IN HEREDITY 



a power of acquiring immunity, of recovering from 

 infection. In this way a short cut is provided 

 by which the much more tedious evolution of 

 inborn immunity is avoided. Measles is an example. 

 The worst, the most death-dealing diseases are 

 those against which immunity cannot be acquired. 

 When immunity can be very quickly and easily 

 acquired the disease is seldom fatal. Death from 

 chicken-pox, for example, is very rare — so rare that 

 no evolution has resulted, wherein it is in violent 

 contrast to consumption, against which there has 

 been immense evolution. 



Alcohol is comparable to consumption in that 

 little immunity can be acquired against it by the 

 individual. The drinker does not become in- 

 different, to any great extent at least, to the 

 poisonous qualities of alcohol. It affects him 

 almost as much at the last as it did at the first. 

 He cannot consume greatly increased doses with- 

 out feeling the immediately poisonous effects — the 

 intoxication. The case is different as regards 

 tobacco. Tobacco is very poisonous to the smoker 

 at first. But, as he becomes habituated to its 

 effects, he is able to tolerate enormously increased 

 doses. He acquires immunity. He can then 

 smoke to his heart's content, generally without 

 remote injury, always without immediate injury. 

 The death-rate from tobacco is therefore extremely 



