The growth of a culture of pneumococcus was followed together with the time relations of some of the phenomena incident thereto. There were, roughly speaking, three periods of growth: first, the period of maximum rate, or logarithmic period; second, a brief stationary period; and third, the period of decline, during which actual death of individual organisms in the culture occurred. It has been pointed out that the usual preliminary latent period was avoided by the use of relatively large inoculum, obtained from a culture which was itself in the logarithmic period of growth.

During the height of growth activity of the culture certain changes in the substrate became demonstrable. Between the 7th and 10th hours the reaction of the medium was changed by the production of acid and the soluble specific substance was detected. At a somewhat later time in the logarithmic period of the culture peroxide was demonstrable and, simultaneously with the appearance of this substance, the substrate acquired the ability to change catalase-free crystalline hemoglobin to methemoglobin. Moreover, changes then occurred in the cultural fluid, such that, after the removal of the parent organisms by filtration, it no longer supported growth when seeded with either the pneumococcus or staphylococcus. These changes occurred early in the logarithmic period of growth of the culture.

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