METHOD OF OPERATION 135 



cations were to be expected. One set of conditions produces 

 (if it acts for a sufficiently long period) the original charac- 

 teristics; another set (by long-continued action) produces the 

 modified characters. The striking feature of these changes in 

 characteristics is that they lag far behind the conditions that 

 finally induce them. When the organisms are cultivated in 

 such a chemical as arsenic, it may be many generations before 

 their resistance to this chemical is increased ; when they are re- 

 turned to "normal" conditions, it may again be many gener- 

 ations before the "normal" resistance is again produced. In 

 either case, the characteristics shown by the organism depend 

 largely on the conditions in which its ancestors of long past 

 generations have lived. 



How are to be explained the adaptive features of the genetic 

 variations induced by environment ? How is to be explained 

 the acquirement, under the action of particular agents, of 

 inherited acclimatization or immunity; increased powers of 

 resistance to these agents ? To attribute such results to a gen- 

 eral quality of adaptiveness does help, for in each example of 

 adaptation the result is always a specific relation between a 

 particular organism and a particular situation or condition; 

 and the question for answer is: How is this specific relation 

 brought about? How is to be explained the acquirement, 

 under the action of a particular chemical, of increased powers 

 of resistance to that particular chemical ? When the organisms 

 are placed in contact with nutritive material which they can- 

 not use, how is to be explained the acquirement of a changed 

 method of metabolism, enabling them to use precisely that 

 material ? 



These questions are identical with those that arise with 

 relation to the powers of direct acclimatization or immuniza- 

 tion that are found in the somatic tissues of higher organisms. 

 There is as yet no assured answer to the questions. In an 



