A Combination Simple Manometer and Constant Volume Differential Manometer for Studies in Metabolism

The purpose of this article is to describe a manometer which we have developed during the past year for studies in metabolism and which appears to include a number of features of wide-spread use and interest. It is a combination manometer, offering in a single apparatus the possibilities of either direct or differential manometric measurements. For direct measurements it is the equivalent of two single manometers of the conventional Barcroft-Warburg type in which one limb of the manometer is open to atmospheric pressure. As a differential manometer it operates at constant volume, with the attendant simplification of differential measurement made possible by the use of constant volume vessel constants. The differential readings are equally significant at high or low vessel pressures, and a sensitive manometer fluid may be used, since only pressure differences are allowed to influence the manometer. It is adaptable for use with a variety of vessel types, and has proved equally suitable for the study of metabolism in Ringer-phosphate solution or in those solutions which must be maintained under physiological conditions of gas tension, such as Ringer-bicarbonate solution, blood serum, and other physiological fluids. Construction-The chief characteristics of the manometer are shown in Fig. 1, which is a drawing of the front and side views of the apparatus.’ It can be seen that the manometer is essentially