The stimulant action of tobacco upon the heart is precisely the same as that of sunlight, which, by inciting the nervous expanse of the retina, indirectly strengthens and accelerates the pulse. So far as the circulation is concerned, there is no difference between the two. The one stimulus may indeed be popularly called "natural," while the other is called "artificial," but such a distinction is physiologically meaningless. The molecular action is the same and the consequences to the organism are the same in both cases. The heart's normal action being facilitated, the blood is poured more vigorously through every artery, every vein, and every network of capillaries. Every tissue receives with greater promptness its quota of assimilable nutriment. And, the web-like plexuses of nerve-fibres distributed throughout the tissues being simultaneously stimulated, the work of nutrition goes on with enhanced vigour and efficacy. Nor is it possible for the excreting organs to escape the influence. Lungs, skin, and kidneys must be alike incited; and the removal from the blood of noxious disintegrated matters, the products of organic waste, is thus hastened. So much is to be inferred from the stimulant action of tobacco upon the medulla. Of all this complicated benefit, the brain receives perhaps the largest share. The brain receives one-fifth, or according to some authorities one-third, of all the blood that is pumped from the heart. More than any other organ it demands for its due nutrition a prompt supply of arterial blood; and more than any other organ it partakes of the advantages resulting from vigorous circulation. The stimulant action of tobacco upon the spinal cord and the cerebral hemispheres is less conspicuous. Yet even here its familiar influence in stilling nervous tremour and allaying nocturnal wakefulness is good testimony to its essentially beneficent character. Wakefulness and tremour are alike symptoms of diminished vitality; and the agent which removes them is not to be called, as Mr. Parton in his mediæval language calls it, "hostile to the vital principle."