The medicinal properties of water as a diluent were well known to the ancients; and cold water, used as a drink in fevers, was the principal remedy of the father of physic in these complaints. The temperature of 60° is the proper degree, when it is intended that water should produce its diluent effects without the aid of heat. Under 45° it produces a sedative and astringent effect; above 60° and under 100°, it relaxes the fibres of the stomach, and is apt to induce nausea, particularly when bulk is added to this range of temperature; but at a higher temperature, the stimulus of heat, in the same manner as the addition of other stimulants, prevents that effect. Simple water may supersede the use of all other diluents; but animal and vegetable infusions are generally employed; or toast and water (infu-sum panis tosti), which is more agreeable to most palates, and is an excellent diluent in fevers and inflammatory diseases. The temperature of water as a diluent should be regulated by the nature of the disease; in internal haemorrhages the temperature should not exceed 45°, but it may be 60° in fevers; unless in the cold stage of the paroxysm of fever, when thirst should be allayed by tepid, or warm water, or other bland fluids; and the same precaution is necessary when the sweat has become general and profuse.

In cases in which there exists a morbid increase of bile, disturbing the functions of the stomach and irritating the bowels, the temperature of the water used as drink may be from 90° to 114°; and in some cases of dyspepsia, which are attended with the sensation of coldness at the stomach, and with cold extremities, a cupful of water, taken as hot as it can be drunk, affords very considerable relief. In cases of redundant bile, by drinking half a pint of tepid water every morning before breakfast, and taking immediately afterwards moderate exercise, the acrid bile is diluted, and its passage through the bowels assisted, without the irritation which, in its undiluted state, it always excites; and it produces the same benefit in cholera morbus in the commencement of the disease, the stomach being rendered by it more fit to receive opiates and other remedies. Some medecines, as sudorifics, diuretics, and emetics, scarcely produce their effects, unless their operation be assisted by copious dilution with water, or watery fluids.

1 The water conveyed to Hoddesdon, in Hertfordshire, rises through a fine white sand, and is so pure, that Dr. Hales affirms it left no incrustation in a boiler which had been in constant use for fifteen years. Statistical Essays, ii. 242.

2 Soap when agitated with hard water is decomposed; the alkali of the soap uniting with the acid of the earthy salts, while the oil and earths combine, and form new, nearly insoluble soaps, which swim in a curdy form on the surface of the water.

3 Percival ascrihes the glandular swellings common in Manchester to this cause. See Essays, i. 291.

Water is also an external remedy of great importance, but its effects are much modified by the degree of temperature at which it is applied.

Cold Water, or of a temperature under 70°, gives the sensation of cold to the skin, and is applied under the form of bath and of affusion-

The cold bath (balneum frigidum) is water of any temperature, from 42o to 85° of Fahrenheit. When the body is immersed in it, it first induces the sensation of cold, excites shivering, renders the skin pale, and contracts it so as to produce the appearance denominated goose skin (cutis anserinu); the respiration at the same time is quickened, rendered irregular, and sobbing occurs. The pulse is diminished in force and velocity, but is rendered firmer and more regular. If the immersion be not long continued, reaction takes place on coming out of the bath; a glow, or agreeable sensation, of heat is felt over the whole body, the tone and vigour of the muscles are increased, a buoyancy of spirit and aptitude for action succeed, and a sense of general refreshment is experienced by the bather. The protraction, however, of the immersion for a considerable space of time, particularly if the temperature of the bath be under 50°, is not followed by this reaction, but the cold water operates as a powerful sedative; the action of the heart and arteries becomes languid, the pulse ceases at the wrist, the animal heat is rapidly diminished, and a sensation of coldness at the stomach is felt, which is succeeded by faintness, delirium, torpor, and sometimes death.

These unpleasant effects are occasionally experienced in some degree, even when the immersion is not protracted, and the temperature of the bath is not under 60°; in which case cold bathing proves always hurtful, and ought not to be repeated: but when the contrary effects are experienced, it is found to be useful in many diseases of debility, particularly in scrofula, if the water be impregnated with salt, or sea-bathing be resorted to. The debilitated, however, in whom the use of sea-bathing produces these effects, when it is employed before breakfast, are not always affected in the same manner when it is used after breakfast, or when the stomach is full; but, on the contrary, they receive the same benefit from it as those with whom it agrees at all times. The use of cold water as a general bath is never employed with a view of producing its sedative effects; put for this purpose it is partially applied, either by the immersion of the affected parts, or by means of cloths dipped in very cold water, and laid over or near the parts.

It is used as a remedy in active uterine haemorrhages, burns, and scalds, and in local inflammations, even when arising from general disease, as gout and acute rheumatism, when the surface of the pained part appears red and inflamed; and in inflammation of the brain or its membrane, in which case it is either applied to the shaved scalp, or dropped upon the vertex.