RELATIONSHIP BETWEEN HORMONES AND EVOCATORS 147 



before they can reproduce. Now if a gene combines with 

 a hormone it is no longer exactly the same body as it was 

 before that combination took place, and it is obvious 

 that it may be unable to reproduce itself during the pe- 

 riod in which it is changed by combination with the hor- 

 mone. Another possibility is that if it does reproduce, it 

 will not reproduce exactly as it was before combination 

 with the hormone, but as a new body: i.e. it may repro- 

 duce as a mutant of the original gene. With these points 

 is mind we can see that the nature of the action of a 

 hormone upon a gene may depend upon the fraction 

 of time with which gene is combined with hormone. 

 If the concentration of hormone is less than a roughly 

 defined concentration, the hormone will affect only the 

 physiological activity of the gene. But if the concen- 

 tration of the hormone exceeds this rough level, the 

 gene may be unable to reproduce, or may reproduce a 

 mutant gene. The possibility of a hormone producing 

 a mutation of a gene by combination with it is itself very 

 interesting. When we consider the case of a primer sub- 

 stance also being required for gene reproduction a num- 

 ber of related alternative mechanisms for the production 

 of mutant genes appear. 



Similarly, if the action of the hormone is directly or 

 indirectly to prevent gene reproduction, then at least 

 two possibilities emerge. One is that the gene or primer 

 may be destroyed in the cell during the period in which 

 it is unable to reproduce. In this case it is treated virtu- 



