146 RESPONSES OF CELLS ON THE BIOLOGICAL LEVEL 



is applied, which remains latent until the damage is 

 revealed by an irritant such as croton oil. We could read- 

 ily understand these results if the irreversible damage 

 caused by the dimethyl benzanthracene is a mutation. 



The Relationship between Hormones and Evocators 



At present it is supposed that hormones are usually in 

 some way connected with the activities of enzymes, and 

 exercise their physiological effect through this connection. 

 The hormones may be prosthetic groups, coenzymes or 

 inhibitors etc. of the enzymes concerned. We also sus- 

 pect that genes consist of a specific array of enzymes. 

 This being so, we are inclined to suspect that hormones 

 and genes may have some fairly direct relationships. 

 A possible source of the relationship between the evocator 

 action and the physiological hormone action of a given 

 substance can be traced if we consider the circumstances 

 of gene reproduction. 



One of the most striking characteristics of genes is 

 their ability to reproduce themselves. We do not know 

 a great deal about the conditions which are necessary for 

 the control of reproduction of genes. But two possible 

 extreme cases can be distinguished. Some genes are 

 perhaps in a cell quite intact at all times, and reproduce 

 themselves in the general environment provided by the 

 cell. Other genes may need additional specific substan- 

 ces present, which may be called primer substances. 



