REFERENCES I49 



gene upon which diniethyl benzanthracene has its effect. 

 There are many other problems which might well be 

 investigated from points of view analogous to that which 

 we have been discussing. For example, some types of 

 leukemia respond well to treatment with urethan for a 

 period, but after that period become resistant to ure- 

 than. Is some phenomenon of mutation or deletion in- 

 volved here ? Then we might, for example, ask whether 

 a sulphonamide-induced agranulocytosis is an instance 

 of gene deletion ? But space does not permit of going into 

 further details in such matters. 



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