A Diuretic effect is very frequently occasioned by substances which act on the stomach and _primæ viæ_, producing a peculiar state of these organs, which _sympathetically_ affects the whole body, and more particularly the absorbent system, and the vessels concerned in the secretion of urine from the blood. As this primary influence upon the stomach, and the effects to which it gives rise in remote parts, are very different in their character, according to the nature of the remedy employed, and the state of the system at the time of its administration; the present attempt to investigate and generalize these relations, and to adopt them as the basis of a classification, may ultimately lead the practitioner to some distinctions of practical utility. 1. _By diminishing Arterial Action, and increasing that of Absorption._ It would appear that the action of the vessels employed in the circulation of the blood, and the energy of the absorbents are, to a certain extent, antagonist powers; the experiments of Majendie demonstrate that the absorption of a poisonous substance is retarded by a plethoric, and accelerated by a depleted state of the sanguineous system; the fact is practically established by numerous phenomena in pathology. Dr. Blackall has very satisfactorily shewn the existence which subsists between increased arterial action and diminished absorption. Hence it follows that remedies capable of controlling the circulation may affect the activity of absorption, increase diuresis, and cure dropsy; in this manner the _Digitalis Purpurea_ acts as a sorbefacient, and it may be remarked that it seldom or never produces its diuretic effects, without a concomitant reduction of the frequency of the pulse; its power too appears only when it is administered in dropsy; in a state of health it will reduce the pulse, but not increase the discharge of urine. Tobacco has also somewhat analogous powers in promoting absorption, and its operation is accompanied with a corresponding depression of vascular action. Venesection, upon the same principle, may occasion, in certain cases of dropsy, a discharge of the accumulated fluid. 2. _By increasing the tone of the Body in general, and that of the Absorbent System in particular._