Diuretics, (from Diuretica 3017 by, and urine). Medicines which are suited to promote the secretion and provoke the discharge of urine, either by increasing the quantity of water in the mass of blood, or by introducing a matter that may stimulate the kidneys. When medicines are designed to pass off by urine, walking gently in a cool air will assist their action; but considerable warmth directs them to the skin, or at least restrains their efficacy.

The object of this discharge is to carry off various substances, either injurious or no longer useful to the constitution. The principal of this is the urea, or, as it is sometimes called, the uric acid. With this we find muriat of potash and soda, phosphat of soda, lime and ammonia, with an excess of phosphoric acid, and an animal extractive matter. The greater number of these are the products of the animal economy, and they arc thrown out as injurious. The animal matter has been styled effete, a word of no very distinct meaning; but, from the symptoms of disease, it appears to be that matter which is no longer adapted for the different functions of the organ of which it makes a part, but is absorbed and evacuated as excrementitious. See Urine.

The importance of this discharge is sufficiently obvious from the facts before us; and, when retained, the most violent symptoms follow. To obviate these, it is often necessary to restore it; and diuretics are medicines by which this object is effected.

From this view it appears that the mere evacuation of a watery liquid is not sufficient. In many fevers the water is sufficiently copious; but we find no portion of the necessary contents, and some febrile complaints are apparently kept up by their retention. We can often procure a mere watery discharge by frequent draughts of fluid; but it is frequently returned as pure as it is drunk; and, in dropsy, where we want only the discharge of fluid, we gain little, if only what we pour in is thus returned.

One singularity respecting this discharge has occasioned considerable surprise; we mean the very short time sometimes required for the evacuation of watery-drinks, and the little impregnation which they receive. It has led to a suspicion that some ducts lead immediately to the kidneys from the stomach: but they have been sought for in vain; and, when we reflect on different facts respecting the secretions, we shall be led to suspect that it is not the same fluid which is evacuated, but that, when a supply is at hand, nature discharges a portion of fluid to prepare for its reception. Thus, at the sight of tempting food, the secretion of the saliva, and probably of the secretions of the stomach,"are increased; and, in the opposite scale, when the child is put to the breast, the sense of thirst is immediately felt.

Watery liquids alone will not excite, in any effectual degree, the action of the kidneys; but, if impregnated with the farinacea, or sometimes only with our indigenous aromatics, so as to become subject to the digestive power, they will succeed. In general, diuretics are to be divided into cooling, sedative, and stimulant. The cooling diuretics are the alkalis, chiefly carbonated, or supercarbonated; for the diuretic power of the pure alkalis is doubtful, except in the form of soap. The carbonic acid, when combined with alkalis in various mineral waters, and sometimes alone in water, is equally effectual; and all the neutrals, with either the fixed or the volatile alkali, occasionally act in the same way: the most powerful of the latter is the acetated ammonia.

Vegetable acids, either native or the product of fermentation, are considered as diuretics, and belong to the first order. All the vegetable fruits, particularly of the senticosae, and all the oleraceous plants, are of a similar nature, though weak in their powers. To assist their action the skin must be kept cool, and every stimulus avoided; indeed, cold alone, or by means of water, applied to the skin, has a similar eftect.

The sedative diuretics are more numerous than authors have supposed. The foxglove is at the head of the list; and the squill, though referable to the following order, seems to owe, in part, its virtue to its sedative power. The tobacco, the wild lettuce, the broom, the ice plant, the winter cherry (physalis alkekengi), the wolf's bane root (doronicum pardalianches), opium, which sometimes acts powerfully in this way, the woody nightshade (solanum dulcamara), the rue and savine, if diuretic, with some others, are of this class. They act, as already explained, under the article cathartics, by the general relaxation they produce as deleterious substances. They are of doubtful efficacy, and should be always used with caution. See Digitalis.

The stimulating diuretics are chiefly vegetable. We borrow one only from the mineral kingdom, though of doubtful origin and efficacy, viz. the naphtha; and two from the chemists, nitrous ether, and oil of wine. Various are the plants arranged among the diuretics of this nature in the authors on the materia medica. Many of the umbellatae; the most effectual of which are species of apium and daucus (parsley and wild carrot roots and seeds); the stellatae; the asparagus, bardana, and seneca; the siliquosae, the alliaceae, coniferae, and liliaceae: of the siliquosae, the erysimum is most effectual; of the alliaceae, the allium and squill; of the conifers, the juniper; of the liliaceae of Murray, the colchicum.

The balsams and resins merit our notice also in this place. The former may derive, in part, their virtue from the benzoic (perhaps the vegetable) acid; but there is reason to think that the oil contributes to the effect. The various turpentines are perhaps the most powerful. The Canada balsam is from a species of pinus, and the Chio turpentine from a similar vegetable, the pistaceae terebinthus. The balsam copaiba, the gum guaiacum, the balsam of Peru, and the gum benjamin, follow in their order; though, as we advance in the list, the powers are weaker, and almost disappear. From some analogy, either botanical or therapeutical, the warm antispasmodic gums have been occasionally added to the diuretics. They may have some effect when the discharge is occasionally checked by spasm; but the olibanum, from a species of juniperus, and the sty-rax, from other analogies, have the fairest claim to our regard as diuretics. Mercury, which is so generally a stimulant, and sometimes acts on all the variety of glands, is occasionally directed to the kidneys.

The more immediate action of diuretics is connected with' the general doctrines of secretion. It is sufficient to remark at present, that the greater number, by their chemical affinity, are confined to that portion of blood from which the urine is derived, the serosity. The stimulant diuretics are said to possess what is styled a specific power on the kidneys. This we must sometimes admit, when a better reason cannot be assigned; but, in this class, the stimulus is by no means confined. Many of the diuretics, by proper management, are sudorific, which may be, in part, explained from their chemical affinity; but they are also expectorant, and occasionally cathartic. In fact, the union of a vegetable acid with a warm oil, which constitutes the balsams and the turpentines, obeys the chemical affinity of either, according to the state of the constitution, or accidental circumstances. Of the action of the sedative order we have already spoken.

Of the use of diuretics in fevers we are not prepared to speak. If the contents of the urine are retained, it will appear, at first sight, an obvious measure to restore the action of the kidneys by diuretics; but the attempt would fail. When the fever relaxes the obstruction, the proper discharge returns; but the cure of fevers is one of the arcana which we cannot yet fathom. It is sufficient if we can assist nature, and conduct them safely to their termination.

The abuse of diuretics, particularly of mineral waters, has been much insisted on. In fact, the long continuance of these medicines, when they produce the discharge, greatly relax the urinary and adjacent organs, and occasion a variety of distressing complaints.

See Hoffman's Med. Rad. Syst. Alexander's Exper. Essays, p. 149, etc.