Oxygen uptake by whole cells or lysed cells ofA.xylinumat pH 8.0 is only 3% of that of the same preparation at pH 6.0. Because the amount of cellulose synthesized by both types of preparation is the same at pH 6.0 and pH 8.0, not more than 3% of the oxygen uptake of cells ofA.xylinumat pH 6.0 is directly linked to cellulose formation. When tomato supernatant is used as a substrate at pH 6.0 an increase in cellulose synthesis is accompanied by a decrease in oxygen uptake by whole cells. Even at constant pH, oxygen consumption is therefore a poor measure of cellulose synthesis. In spite of the large fractions of available glucose incorporated into cellulose, only a very small part of the total metabolism of the organism is devoted to synthesis of cellulose.