4,: 



time of treatment in min. 



Fig. 17A. The induction of reverse mutations. Reversion induction of BU induced 

 mutants by nitrous acid (see E. B. Freese and E. Freese, 1961). 



Fig. 17B. The induction of reverse mutations. Reversion induction of an EES- 

 iuduced mutant (66) by EES and low pH. This mutant does not respond to nitrous 

 acid (NA) or to hydroxylamine (HA) (see E. B. Freese, 1961). 



259 



