NUCLEAR SEGREGATION AND THE DELAYED APPEARANCE OF INDUCED MUTANTS IN ESCHERICHIA COLI

The existence of a cytologically demonstrable nucleus in the bacterial cell is no longer seriously in question. There is, however, no direct evidence that the Feulgen-positive staining bodies generally considered to represent the nuclear or chromosomic elements of the bacterium are actually carriers of genetic material. The chromosome theory of heredity has yet to be established for bacteria. Current acceptance of the bacterial nucleus as a cytological entity stems largely from the work of investigators who demonstrated bodies having typically nuclear reactions to stains and enzymes (Stille, 1937; Piekarski, 1940; Robinow, 1945; Tulasne and Vendrely, 1947, among others). Although there is no general agreement among bacterial cytologists as to the finer organization and structure of the nuclear body, and as to its pattern of division (see Delaporte, 1950; Bisset, 1950; Knaysi, 1951), the observation that serves as the starting point of this investigation is, I believe, sufficiently conservative to find general acceptance: namely, that the number of visibly distinct nuclear bodies (or chromosomes, or nuclear elements) is larger in logarithmically dividing cells of Escherichia coli than in resting cells.