By the aid of glass electrodes changes of medium pH were determined during glucose metabolism according to the combinations of various concentrations of phosphate buffer, glucose, and bacteria, using such resting cells as E. coli, Aerobacter aerogenes, Sal. typhi 57S and 57R, Sal. paratyphi A and B, Staphylococcus aureus, albus and citreus, and further the volumes of more important acids produced at differnet time measured. Next, the relationships between these volumes and “time-pH” curve were studied; and the following are the conclusions arrived at. 1. "Time-pH" curves in the case of E. coli present moderate descent on the whole whereas in the case of A. aerogenes they were steep; and the production of acetoin and lactic acid is very much but that of α-ketoglutaric acid lesser in the case of the latter. 2. In the cases of Sal. typhi 57S and 57R, the fall of pH in the former is steeper than that of the latter, and the production of lactic acid has been alomst twice that of the latter. 3. Of the bacteria tested, Sal. paratyphi A and Sal. paratyphi B was steep in the fall of pH and the production of lactic acid was greater though that of pyruvic acid is small. 4. The rates of fall of pH are greater in the order of St. aureus, St. albus and St. citreus; and St. aureus is influenced quite sensitively by the concentrations of phosphate buffer and glucose. Moreover, these changes in concentrations alter the order mentioned above. 5. Main cause of the fall of pH in the case of the test bacteria seems to be lactic acid followed by pyruvic acid.