338 EVOLUTION, GENETICS, AND EUGENICS 



ment. However, it is still a question whether the material used may 

 not be heterogeneous as regards the germinal factors that condition 

 certain physiological characters. 



Stockard's investigations on the effect of alcohol on the progeny 

 of guinea pigs have shown that the germ cells as well as the somatic 

 tissues of the alcohohzed animals are injured. 



On the whole it must be admitted that the experimental induction 

 of heritable variations is still largely an un worked field. The complex 

 conditions to be considered and consequent obstacles to be overcome 

 are appreciated by no one more fully than by those who have at- 

 tempted such investigations. For, as Tower has said: "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 

 httle 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 production 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." 



