Realizing that the optical density of phosphate buffer suspensions of E. coli and Aerobacter aerogenes, Sal. typhi 57S and 57R, Staphylococcus aureus and albus at the wave length of 537 mμ changes at the time of glucose metabolism, changes of viscosity, viable counts, and the changes in the volumes of proteins, ribonucleic acid, desoxyribonucleic acid composing bacteria have been pursued and the results are as follows. 1. During the glucose metabolism of buffer suspensions using the bacteria mentioned above a rise of optical density can be observsd and the rise has usually a parallel concern with time incubated. 2. Accompanying the rise of the optical density the increase in the relative viscosity and increase of ribonucleic acid and proteins can be recognized. Assimilation and synthetic action can also be seen during the glucose metabolism. Changes of optical density have been found to be inhibited by antibiotics and thus this factor has been utilized in simple examination of antibiotics.