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E have undertaken a study of several mutagens to determine their usefulwness in the isolation of deletion mutations in Escherichia: coli. No systematic investigation of deletion inducing agents in E. coli has been described. A related study is that of TESSMAN (1962) who has shown that a high proportion of T4rZZ mutations induced by in uitro treatment with nitrous acid are deletions. In addi-
Schwartz et al. (Sat,) studied this question.