The adaptation of Bact. lactis aerogenes to high concentrations of proflavine

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Abstract
When trained by successive subculture in the presence of proflavine at a given initial conc. up to 200 mg. per liter, Bact. lactis aerogenes acquires the ability to grow without lag at concs. up to, but very little exceeding, the initial conc. After adaptation to higher concns., however, considerable adaptation may result; cells trained at 1500 mg. per liter, for example, growing immediately (provided they are of suitable age) at any conc. up to 3000 mg. per liter. The complete adaptation is not initially stable. Cells trained to grow at 2000 mg. per liter pass through the following stages: adaptation incomplete; adaptation complete (that is, cells grow without lag) but unstable; and adaptation both complete and stable. In the unstable phase reversion occurs to a lower state of adaptation. The stable state is only reached after very prolonged training. An induced loss of adaptation occurs when the cells are grown under appropriate conditions in the presence of phenols. The selection of resistant types is considered to be an inadequate explanation of these facts. The authors prefer a theory of enzyme expansion and modification, although the superposed operation of selection on the other changes provides an explanation of certain quantitative facts about the phenol-induced reversion.

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