GENE MUTATIONS 53 



duced a lot of gene mutations, to which are due the inherited 

 abnormalities, weaknesses and other aberrations. The number 

 of visible mutations produced under the action of radiation is 

 about seventy-five times as great as occurs without radiation. 



This effect of radiations in producing mutations was con- 

 firmed by others and extended to other organisms. Radiations 

 from radium have the same sort of effect as X-rays; they 

 greatly increase the number of gene mutations. Gene muta- 

 tions have been produced by radiations in maize, barley, 

 tobacco, cotton, various animals, and many other organisms. 



By radiation the same types of mutations are produced as 

 occur spontaneously. In many cases the mutations due to the 

 radiations are identical with others that had occurred without 

 radiation. Others induced by radiation differ from any before 

 observed. The same gene may be caused by radiation to pro- 

 duce repeatedly in different individuals the same mutation. 

 Since all kinds of mutations are induced by radiation, it is 

 clear that there is here no relation between the kind of muta- 

 tion produced and the kind of environmental agent that 

 induces them. The mutations induced by radiation are inher- 

 ited in later generations, as are those that occur spontaneously. 



The number of mutations produced in a given number of 

 individuals is found to increase in proportion to the energy of 

 the radiation; that is, to its intensity and duration, up to an 

 energy that causes injury so great that the radiated germ cells 

 do not develop. 



The question arises as to whether the "spontaneous" muta- 

 tions are not partly or wholly the result of radiations occur- 

 ring under natural conditions. It was found that fruit flies 

 kept in a mining shaft in which natural radiation from the 

 minerals present was abundant gave a larger proportion of 

 mutations than those kept under usual conditions, indicating 



