The more rapidly the blood is carried through a secreting structure, the greater of course is the amount which comes, within a given time, in contact with that surface, and the more copious must be the secretion. Whatever stimulates the circulatory system, should circumstances prevent a free action of the skin, and especially should they favour a tendency to the kidneys, will produce diuresis. Heat does not, because it favours perspiration. Neither does active exercise, as a general rule; because, though it accelerates the action of the heart, it also has a disposition specially to affect the skin. But stimulation, with coldness, and especially with vascular fulness, greatly promotes the function. Every wine drinker knows the effects of indulgence in that beverage at table. So is it with the other forms of alcoholic drinks, especially the spirituous liquors, and beyond all others gin, which contains a special diuretic ingredient in the oil of juniper. The ethereal liquids have the same effect; and I have often known even the salts of morphia, notwithstanding their ordinary effect in diminishing the secretions, to act as an energetic diuretic. it is not, however, the pure arterial stimulation in these cases that operates; for the stimulant substance itself, on entering the blood-vessels, often excites the kidneys directly, as well as the heart.

This, like the two preceding influences, may, if carried too far, produce an excitement in the kidneys beyond the point at which they are disposed to secrete, thus obeying one of the universal laws of irritation.