This article is only available in the PDF format. Download the PDF to view the article, as well as its associated figures and tables. The effect on metabolism of varying degrees of hydration has received but little attention. Our metabolic laws have been assumed to apply rigidly and quantitatively, whether the body was supercharged with water or dehydrated to the point of anuria. Such an assumption is theoretically unsound. One would not expect chemical changes to occur with the same results, either quantitatively or qualitatively in solutions of different strengths. Hitherto, investigators have assumed that this was the case and water metabolism has only been studied in relation to edema, acidosis, nephritis, fevers and the general theory of flushing out or diluting toxins. The following experiments show that the problem is deeper and the varying concentration of the tissue fluids produces profound changes in what have previously been regarded as independent metabolic phenomena. The injection of equivalent amounts of insulin into animals has been expected to bring about a fall in the blood sugar