As the pigmentation of the skin and mucous membrane is not invariable, and since it may occur without disease of the capsules, it is not improbable that it is due to disease of the abdominal sympathetic ganglia, which are usually affected at the same time as the capsules. The suprarenal capsules are composed of columns of epithelial cells, which radiate from a large vein in their centre. They are abundantly supplied with blood and with nerves. The cells near the vein are much larger than those in the peripheral portions of the columns. Amongst them are nerve-cells resembling those of the sympathetic system. The history of the suprarenal capsules is almost as obscure as that of the thyroid gland. In the embryo they are relatively very large—larger at one period than the kidney. At this period bloodvessels are formed in them with great rapidity by a curious process of boring through and channelling out of their cells. There are other facts connected with their development in the individual and their varying form in different classes of vertebrate animals which point to a “previous existence,” but there is nothing to indicate that they were ever open glands. In all vertebrates they are closed masses of cells, the only function of which, so far as we know, is to produce an internal secretion; but the importance of this chemical messenger in bringing about the proper working of other organs is almost startlingly evidenced by the collapse which follows disease, or removal of the organ which produces it. The suprarenal capsules yield a substance which has been termed “adrenalin.” It contains nitrogen, is crystallizable and dialysable; but its chemical relationships have not been made out as yet. It is not destroyed by boiling, nor by digestion with gastric juice. Injected into a vein, it causes, amongst other effects, an immense rise in blood-pressure, even though the amount injected be extraordinarily small. Applied locally as a wash or spray, a solution of 1 part in 10,000 produces marked blanching of the surface; and it is useful, in consequence, as a means of checking bleeding in small operations, especially those on the eye or the nose. It is a most energetic poison. Even ¼ milligramme is sufficient to kill a rabbit. In short, adrenalin acts like the most powerful drugs known to physicians; and this drug, manufactured by the suprarenal capsules, is constantly added to the blood. Disastrous consequences follow a failure in the regular supply.