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.