It is well known that glutamic acid, as well as aspartic acid, plays an important role in the metabolism of microorganisms. The author performed many experiments in order to study the physiological aspects of E. coli communis from the stand point of glutamic acid metabolism, and to apply it to the analysis of glutamic acid. The results were as follows: 1) E. coli can grow at any pH within the range from 5.4 to 8.0, but the growth is the best at pH 6.8 to 7.0. 2) The more remote from the optimum the cultural pH is, the nearer it comes to the optimum after the growth. This phenomenon is particularly remarkable on the acid side. 3) Using glutamic acid as substrate, the decarboxylation is chiefly carried out on the acid side, the deamination on the neutral or slightly alkaline side, and these two reactions are carried out simultaneously at pH 5.5 to 6.5. As for the optimum pH, pH 5.0 for decarboxylation and 7.0 for deamination. 4) The lower the cultural pH is, the higher the glutamic decarboxylase activity of the cultured organism becomes. The optimum reaction pH is, however, never shifted. 5) The E. coli, which was cultured in the pyridoxin-containing semi-synthetic medium, shows a very high activity to glutamic acid, but not to α-ketoglutaric acid, aspartic acid, alanine and pyruvic acid. 6) The aceton powder of the E. coli, which was cultured in the pyridoxin-containing semi-synthetic medium, still has the high glutamic decaboxylase activity. The optimum pH is from 4.4 to 5.1, where carbon dioxide is evolved quantitatively.