—The fetus and infant under one year have two organs in the retroperitoneal space on each side of the aorta, a little below the inferior mesenteric artery. They are about 11 mm. in length, and correspond in structure to the medullary substance of the suprarenals. They are abundantly supplied with blood vessels, and consist of a close network of capillaries with large polymorphous cells which stain yellow with the chromin salts. Biedl has found that an extract of these organs has the same effect in intravenous injection as suprarenal extract. This indicates that the action of suprarenal extract is due exclusively to the medullary substance and is the property of all chromophilous cells.