Physiological Youth as an Important Factor in Adaptive Enzyme Formation.

It has been known for many years that bacteria, cultivated upon a specific substrate, may not ferment other materials unless cell multiplication occurs. Karstrdm (1930) observed that cells grown in the presence of one sugar, then suspended in solutions of other sugars under conditions preventing multiplication, could not ferment the new sugars for long periods of time, if at all. Stephenson and Strickland (1933) showed that there was no natural selection in the case of formate adaptation by Escherichia coli and that the formation of the enzyme can occur while no cell division is taking place. Stephenson and Yudkin (1936) observed that top yeasts can adaptively ferment galactose without cell multiplication but no adaptation could be obtained with cultures incapable of growth. They state, however, that a study of their total and viable counts suggests that it is not the viable cells alone which are capable of adaptation. Stephenson and Gale (1937) found that the galactozymase of Escherichia coli was formed only when growth occurred in the presence of the specific substrate. This adaptation was proportional to the number of cells which had divided in the presence of the galactose. The following experiments are the result of a search for the factors controlling the mechanism of adaptation. Old cells adapt themselves slowly if at all (Karstrom 1930) and young, growing cultures produce the new enzyme easily. Therefore, experiments were designed to test cells of various ages and to determine