THE CONTROL OF LIFE 109 



therefore appear that an efiFect upon the 

 body cells can be transmitted to the germ 

 cells. But it is too soon to draw any far- 

 reaching conclusions from this series of 

 experiments, especially as disturbances 

 of equilibrium sometimes appear in rats 

 which have not been subjected to treat- 

 ment. We must be the more cautious 

 in this regard as a great many experi- 

 menters have vainly sought to prove the 

 inheritance of acquired characters and 

 have reached the conclusion that such 

 inheritance is extremely doubtful. 



One of the most important problems 

 of biology is to discover how changes are 

 produced in the germ cells. One way of 

 attacking this is to observe imder what 

 conditions spontaneous changes occur in 

 germ cells which produce the so-called 

 mutations. Such mutations are now ac- 

 cessible to observation in considerable 

 numbers. Over three hundred of them 

 have been observed by Morgan and his 

 co-workers in the fruit fly {Drosophila), 

 These embrace the most diverse features. 



