A Note on the Production of Acid by Pneumococci. by Glenn

The latent period of growth or "lag," first recognized by Mfiller in 1895,1 is the time interval between the inoculation of a medium and the beginning of growth at the max imum rate. Chesney concluded that the latent period in the growth of bacteria is an expression of injury which the bacterial cell has sustained from its previous environment3 This conclusion was based upon the observations that the latent period was evident only when the cultures used in inoculation were no longer growing at the maximum rate, and that pneumococci cultures at the end of the period of maximum growth contain a substance that inhibits the growth of actively growing pneumococci. In studying the nature of the influence which the products of metabolism exert upon the further activity of a microorganism it is important to investigate the changes which may have occurred in the hydrogen ion concentration of the medium. The question of the influence of hydrogen ion concentration has been reviewed exhaustively by S/~rensen, ~ by Michaelis, 4 and more recently by Clark and Lubs3 Clark and Lubs emphasize its importance as one of the factors controlling bacterial growth thus: "Just as we pay attention to the temperature of the incubator, so should we pay attention to the hydrogen ion concentration of the medium." We therefore undertook to study the hydrogen ion concentration of actively growing pneumococcus cultures. 6