THE VOLUME OF THE EXTRACELLULAR FLUIDS OF THE BODY 1

Changes in the volume of extracellular fluids of the body can be calculated from the exchanges of sodium (1) or of chloride (2), appropriate corrections being made when necessary for changes of concentration of these ions in the fluids (2). Such studies are technically difficult and time-consuming and yield no absolute values for volume of extracellular fluids. A diffusible, non-metabolized substance not normally present in the body but which, like sodium and chloride, is restricted to extracellular-fluids would afford a convenient measure of the absolute volume of these fluids at any time. The experiments which follow represent an attempt to find such a sub-stance. Sucrose injected intravenously was tried first because it was known that this substance tra-verses capillary membranes with ease and yet does not enter red blood corpuscles. Later, the results of experiments of Crandall and Anderson (3) on the distribution of sulfocyanate suggested that this substance might be of use. Still later, the distribution of sulfate was studied when it was noted from the data of earlier experiments fol-lowing the intravenous administration of Na2SO4 to dogs (4) that sulfate apparently distributes it-self through only about 20 per cent of the body by weight