That a typical diuresis follows the ingestion of large amounts of water has been known for some time, but the mechanism by which the water is conveyed from the intestine to the kidneys and the factors stimulating the kidneys to action, whether they are hormone, vascular, nervous, or physicochemical, are not yet proved beyond question. Engel and Scharl,1 using the refractive index of the serum, Macallum and Benson,2 using the red blood cell count, Haldane and Priestley,3 and Adolf,4 using hemoglobin determinations, found that no dilution of the blood is measurable by these methods when large amounts of water are drunk, although a marked diuresis is produced. Priestley5 did not find any dilution of the hemoglobin, but a decrease of from 2 to 5 per cent in the conductivity of the serum, indicating a proportionate dilution of the plasma electrolytes. He also found that when an almost istonic salt solution