DRUG ACTION UPON GENES I45 



suitable reagents we may expect genes to be very un- 

 stable, and it is possible that the morphogenetic evocators 

 and the more potent carcinogens are such reagents. 



If the hypothesis just formulated should prove to be 

 correct, we should have a profitable line of approach to 

 a number of biological problems. As a particularly in- 

 teresting example we may take the work of Berenblum 

 on the induction of cancer by croton oil and dimethyl 

 benzanthracene. When croton oil is applied alone to the 

 skin of a mouse hyperplasia rapidly develops, but nor- 

 mally no tumours will develop during the natural life 

 of the animal. If dimethyl benzanthracene alone is 

 applied to the skin of a mouse hyperplasia results and 

 after some period tumours commonly develop. If both 

 croton oil and dimethyl benzanthracene are applied 

 together, tumours appear significantly more rapidly than 

 when dimethyl benzanthracene is applied alone. Even 

 more striking is the fact that if just one application of 

 dimethyl benzanthracene is made, tumours appear after 

 a rather protracted period. But if, after the application 

 of dimethyl benzanthracene, croton oil is applied, tu- 

 mours develop much more rapidly and there is a strong 

 tendency for the appearance of the tumour to occur at 

 a standard time after the application of croton oil, rather 

 than after the application of dimethyl benzanthracene. 

 At present the only possible interpretation of these re- 

 sults is that dimethyl benzanthracene rather readily 

 causes an irreversible change in the cells to which it 



