These are drinks which simply dilute the various liquids of the body, without dynamically modifying its condition or functions. Water is really the only diluent; for, however it may be qualified in relation to sensible or nutritive properties by the substances added, though it may be made more grateful to the palate, and may accomplish other purposes incidentally, it is obvious that these additions do not affect the characteristic result. Nor is there any other liquid, so indifferent in its effects, as to be a fit substitute for water for this special purpose. Even water itself is not without a positive dynamic operation on the system. I have already shown that, in excess, it is directly and universally sedative, and may even be made to reduce the vital actions to a point incompatible with life. It is only when in exact correspondence with the wants of the system that it is indifferent in its operation, neither elevating, depressing, nor perverting the normal actions. As a pure and exclusive diluent, therefore, it must be given only in correspondence with these wants; but it almost always happens that, when there is an indication for dilution, there is no contraindication for a moderate sedative influence from water, locally or generally; and if it happens to be given in quantities beyond the necessities of the system, no injury results.

Aqueous drinks operate as diluents in every stage of their progress through the system. In the first place, they dilute the liquid contents vol. ii. - 52 of the stomach and bowels; secondly, they are absorbed and dilute the blood; and, lastly, they are thrown off by different emunctories, and serve to dilute the secreted liquids, as the perspiration, bile, saliva, and urine, particularly the last.

They act beneficially by rendering the different liquids less irritating, and sometimes by facilitating, in consequence of an increased tenuity imparted to these liquids, their course through their various passages. in relation to the former effect, they are useful, as a general rule, in all irritative or inflammatory affections of the surfaces over which they pass, and in cases in which the liquids themselves are morbidly irritating. Let us trace the diluent liquid through its route, and note its therapeutic effects.

The stomach may contain acrid matters, which not only irritate the gastric mucous membrane, but give rise to various morbid sympathetic phenomena, especially headache. A drink of water often affords relief by diminishing the acrimony of the offending cause, until nature shall remove it in the ordinary operations of the alimentary canal. I have repeatedly known sick-headache, dependent on gastric irritation, to be completely relieved by a tumblerful of water, without any other observable effect. Hence, too, one of the advantages of free dilution in cases of acrid poisoning. But the gastric mucous membrane may be irritated or inflamed, independently of its contents, which, nevertheless, though normal in their character, operate as an irritant to it in its more sensitive condition. Here, too, diluent drinks are often of advantage, and, if taken in small quantities, and at a temperature in accordance with the indications, may afford relief simply by diminishing the irritant action of the gastric liquids. Cold water, in small quantities, frequently administered, is not only very grateful, but may be positively useful also in gastritis. These remarks are equally applicable to irritating contents of the bowels, or an inflamed state of the intestinal mucous membrane. Diluent drinks are, therefore, serviceable in diarrhoea of irritation, enteritis, and dysentery.

Following the drinks into the blood-vessels, we find them often of great service by rendering the blood less irritating, in all fevers with thirst and a hot skin, and in all acute inflammations. in some instances, too, when the blood is thickened by loss of its serosity, the water answers a good purpose by restoring the normal fluidity. On this principle, it probably does good in cholera.

When thrown out with the secretions, we find the diluents peculiarly useful in irritative diseases of the urinary organs, and in acrid states of the urine. Hence their beneficial effects in nephritis, pyelitis, cystitis, urethritis, various forms of gravel, and strangury from acrid impregnation of the urine, as under the use of cantharides or the oil of turpentine.

As regards their effects in thinning inspissated liquids, there is reason to think they are occasionally more or less beneficial in facilitating the discharge of most of the secretions; as of the tenacious mucus from the bronchial tubes, the inspissated bile from the biliary ducts, and the thickened urine from the uriniferous tubules of the kidneys.

In the administration of these liquids regard should be had to the choice of the patient, the demands of the stomach, and various coincident indications. Sometimes pure water is preferable to any form of admixture. Generally it may be rendered more agreeable to the palate by saccharine and acidulous additions, and various flavouring substances, and may be made the vehicle of sufficient nutrition to the system, by dissolving in it some gummy or amylaceous substance. in febrile diseases, acids are not only grateful, but useful as refrigerants. in irritable states of the stomach, carbonic acid water is often a very appropriate and useful adjuvant. in debility, the diluent may be rendered somewhat stimulant by wine or spirit.

As examples of drinks of this kind, of which the practitioner cannot have too many at his command, to meet the wants and caprices of the patients, or the various calls of disease, may be mentioned, molasses and water; sugared water; toast-water; barley-water; solutions of gum arabic, arrow-root, tapioca, and sago; infusions of flaxseed, slippery-elm, benne leaves, and sassafras pith; lemonade; orangeade; apple-water; tamarinds and water; currant or blackberry jelly diffused in water, and carbonic acid water; and not a few others might be mentioned. As a general rule, they should be administered cool or cold, and in small quantities at a time; though conditions sometimes exist, in which both these directions may be contravened with propriety; as for example in sick-headache, in which a tumblerful of warm water, swallowed at once, is more useful than an equal quantity taken cold, and in repeated draughts.