Excess of liquid in the blood-vessels is an abnormal condition, which seeks relief either through the skin or kidneys. if one outlet is closed, the other must in some degree supply its place. Therefore, fulness of the blood-vessels acts as a diuretic, whenever circumstances interfere with the diaphoretic function. Cold has been already stated to have this effect, and to operate as a diuretic even without special fulness of the circulation. But its effect is much increased when this latter condition exists. The drinking largely of cool liquids produces the condition through the rapid absorption of the water. Hence, cool drinks are often powerfully diuretic. The same effect, to some extent, is produced by the injection of water into the bowels. immersion in a bath often also disposes to diuresis, while the body is still immersed, and afterwards, if its temperature has not been such as to produce diaphoresis upon exit from it.

It was formerly thought that drinks should be curtailed as far as possible, in the treatment of dropsy, under the apprehension that they might increase the effusion. But any effect of this kind is at present believed to be far overbalanced by their influence in favouring the action of the kidneys, especially when taken cold, and accompanied with diuretics.

It has been supposed that some medicines act as diuretics by promoting the absorption of effused fluid, and thus distending the bloodvessels. But it is clear that they have, in consequence of this property alone, no special influence on the kidneys; for it depends altogether on circumstances, whether the effect of this fulness shall be directed to the skin, the kidneys, or, perhaps we might say, the bowels. Should they, however, combine a real affinity for the kidneys, with the property of promoting absorption, they might act with peculiar energy; and this may possibly be one cause of the extraordinary efficiency of digitalis.

It does not necessarily follow that fulness of the blood-vessels should increase the secretion of urine, even when favoured by an unperspiring state of the surface. if the blood is rich as well as abundant, it becomes too stimulant to the kidneys, and may excite an irritation beyond the point of secretion.