Modification of Germinal Constitution of Organisms 265 



changes immediately before and during maturation. This 

 period is known to be a critical one in the life of the germ cell, 

 and is a time when many processes are in progress, and when 

 there exists a delicate balance susceptible of being per- 

 manently upset. There is evidence hi some of my experi- 

 ments to show that earlier periods in the life-history of the 

 egg are susceptible to stimuli and produce at these earlier 

 periods more profound modifications than are produced 

 later, but are more difficult to induce. During the growth 

 period there is a constantly increasing elaboration of poten- 

 tialities, with an increasing array of substances and sym- 

 metries, and a slight change in this primary constitution 

 might result in large end results. 



It is evident that the problem of germinal change is one 

 of difficulty, and involves more of indirect than of direct 

 methods of investigation. There is little reason to expect 

 that present biochemical methods can give a solution, but 

 they may give valuable suggestions for further indirect 

 investigation. It seems not improbable, however, that 

 this problem, like so many others in biology, must await the 

 solution of the larger question of what life is before it will 

 be possible to express in exact terms the nature of germinal 

 changes. Our present status, with several methods of pro- 

 duction and much knowledge of the behavior of induced 

 germinal changes available, is a basis from which great 

 advances in knowledge and in operation may reasonably be 

 expected. 



