"The composition of tissue cells cannot, like that of blood cells, be determined by direct analysis, because these cells cannot be separated from the interstitial substance which surrounds and connects them. The existence of the latter cannot be questioned; its volume and character defy direct measurement." So writes Peters1 in a comprehensive survey of the exchange of fluids in the body of man. The question as to whether clinical edema represents an increase in the volume of cells or of interstitial tissue fluids or of both has been the subject of some controversy in the past. While the interchanges of fluid and electrolytes that take place between the red blood cells and the plasma are now well described, the limitations mentioned by Peters have prevented any such precise description of similar exchange between the blood and the tissue cells.
By an ingenious combination of analysis and calculation, Eichelberger and
THE EXCHANGE OF SALT AND WATER BETWEEN MUSCLE AND BLOOD. JAMA. 1937;108(22):1893–1894. doi:10.1001/jama.1937.02780220051014