96 THE CONTROL OF LIFE 



nutritional, and (c) environmental modifications. It is 

 usual to include the food as one of the environmental 

 influences, but to the ordinary layman this often seems 

 quaint. 



Frequent Misunderstandings. — As every thoughtful 

 inquirer has to make up his mind in regard to the import- 

 ance of modifications or ' nurture-effects ' for the indi- 

 vidual and for the race, a few explanations may be of 

 use to obviate misunderstandings which are of tedious 

 recurrence. 



(a) A temporary change which does not persist after 

 the inducing conditions have ceased to operate may be 

 called an ' adjustment ' or ' accommodation,' and use- 

 fully distinguished from a modification, which lasts. 

 It is not pretended, however, that any hard and fast 

 line can be drawn. 



(6) A modification is a ' nurture-effect,' but that is 

 not precise enough, since normal development always 

 means an interaction between the hereditary nature and 

 the appropriate nurture. A modification is a structural 

 change directly due to a peculiarity or change in nurture. 



(c) In continuation of what has just been said, it 

 should be noted that the list of modifications in the 

 strict sense should include only the direct new results 

 of peculiarities of nurture. A change in nurture often 

 serves as the liberating stimulus of a character or quality 

 which remains unexpressed in the ordinary environment. 

 For many organisms have, as we have seen, alternative 

 possibilities in their constitution, the expression of the 

 one or the other depending on the available nurture. 



