1. The optimum hydrogen ion concentration for the growth of the various types of pneumococcus is a pH of about 7.8.

2. The limiting hydrogen ion concentrations for the growth of pneumococcus are a pH of 7.0 and a pH of 8.3.

3. Phosphates used in adjusting reactions of media retard growth if present in a concentration greater than 0.1 molecular.

4. Culture media for pneumococci should, therefore, have an initial reaction between a pH of 7.8 and 8.0 and a total salt concentration not exceeding 0.1 M.

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