90 THE REALISATION OF THE NUCLEAR FACTORS 



used up in the course of development. For that reason, the 

 neutral term "gene substance" is nowadays preferred. 



Recent experiments by Beadle and coworkers on mutants of 

 the fungus Neurospora give strong support to the hypothesis 

 that the primary action of genes consists of the production of 

 certain enzymes. Their results indicate that each gene gives 

 rise to one definite enzyme, so that mutation of the gene causes 

 a link in the metabolic processes to fall out. It is conceivable 

 that genes generally exert their influence on development in 

 this way. However, we must await further data on this point 

 before a final conclusion can be drawn. 



