A certain proportion of water is essential to health and life. it is necessary, mechanically, in order to give a due mobility both to the liquids and solids, enabling the former to move from point to point as may be required by the wants of the system, and the latter to act mole-cularly, or in mass, in the performance of their several functions. it is also necessary, dynamically, in order that a proper balance may be maintained between the excitant agencies and the susceptibilities of the system; in other words, that the fluids, which serve to keep the various functions in their healthful state of action, should be neither excessively nor deficiently excitant. it is obvious that an excess of water must, in both these relations, have a sedative effect. in the first place, if in quantity more than sufficient to enable the constituent molecules of the tissues and the blood to move duly in the exercise of their offices, it must have the effect of separating them beyond the sphere best adapted for their mutual reaction, to lessen, consequently, the vital cohesion between them, and thus to occasion at once relaxation of the tissues themselves, and a failure in their functions. in the second place, a similar excess, by diluting the fluids of the body, disturbs the balance above referred to between the excitant agencies and the vital susceptibilities, diminishing the force of the former, and consequently the functions which depend upon a due excitation of the latter. it follows that a universal reduction of the vital actions must ensue from an excess of water in the system; and a similar reduction in those of any one part to which this excess may be confined. But it is not a diminutioa of function only that takes place. There is for the time being a positive reduction also of power. The tissues, of which the molecules or ultimate organic constituents are too far separated to be capable of due mutual reaction, have no longer the healthy capacity of receiving impressions, or of performing function. Their excitability and strength, as well as their action, are depressed. Hence one great difference between the sedative properties of cold and those of water. The former depresses action, but leaves the power unimpaired, while the excitability is increased by rest. it is, therefore, followed by reaction, and thus proves secondarily stimulant. The latter is purely sedative, and is followed by no reaction. The difference is highly important in a practical point of view; as it renders water often applicable as a sedative, when we might be deterred from employing cold by apprehension of the reaction which must ensue.

But there is one aspect in which an excess of water may seem to be stimulant. in order that it may be eliminated, the urine, perspiration, and pulmonary exhalation are increased; and the functions by which these effects take place may be supposed to be stimulated by the liquid. The exception, however, is merely apparent. it is not the characteristic ingredients of the urine or perspiration, nor the proper secretion of the bronchial mucous membrane that are thus increased; it is merely the proportion of water. The proper secretory function is not augmented, but simply the mechanical elimination of water consequent on the distension of the vessels. it is highly probable that the true secretory function, the result of the cell action, is diminished with all the other functions. This effect of water in apparently promoting the secretions will be noticed more particularly under the diuretics and diaphoretics; at present we are concerned only with its obvious sedative effects.

1. Effects On The System

It results, from what has been said above, that water is sedative partly by diluting the blood and other fluids of the body, and thus rendering them less capable of exciting the various functions, and partly by entering into the solid tissues, separating their ultimate organic constituents, and thereby diminishing their vital cohesion, and their power to act. it has these effects, whether swallowed, injected into the rectum, or applied to the surface of the body. I am disposed to think that it owes part of its sedative effect, when locally applied, to absorption into the blood-vessels and depreciation of the quality of the blood, not by dilution only, but by causing a swelling and rupture of the red corpuscles; an effect well known to result from the admixture of the red corpuscles with water out of the body. it has been denied that water is absorbed from baths; but the fact that it is so appears to be incontrovertibly established by the experiments of Dr. Willemin.* in estimating the effects of water, it is necessary to take into consideration its relations with caloric. When applied to the body so as to cause the sensation either of heat or cold, it is not the water only that acts, but the temperature, and the latter mainly. Hence, hot water is stimulating, and cold water directly depressing, but indirectly stimulant through reaction. The peculiar influence of the fluid is apparently lost in that of the heat or cold. To obtain the unmodified effects of water alone, we must employ it at the temperature of the surface to which it is to be applied. it must feel neither hot nor cold, but simply lukewarm when used externally, and in a slight degree warmer when taken into the stomach, so that it may have the same temperature as that organ. This is a practical rule of the utmost importance in the use of water as a sedative. By erring on either side, we fail to procure the intended effect; stimulating directly or indirectly, instead of depressing without tendency to reaction, which is the characteristic operation of water itself. it is, therefore, of warm or lukewarm water - that is, of water alone, unmodified by temperature - of which we are now to treat.

* The following conclusions, in relation to the influence of the bath, were drawn by Dr. Willemin, inspector of the Waters of Vichy, in France, from elaborate researches into the subject. 1. Water is undoubtedly absorbed. 2. The weight of the body, however, is not materially altered; but this is rather a proof of absorption than otherwise; because, in the same length of time, the body in air loses considerably in weight. 3. The cutaneous exhalation continues while the body is in the water, as proved by chemical examination. 4. The proportion of absorption does not depend on the density of the water, nor on its mineral impregnation, but apparently on the physiological condition. 5. iodide of potassium is absorbed, as proved by its existence in the urine; but a certain quantity of the salt in the bath is necessary to this result. When the bath contains 100 grammes (1543 grains), the iodide will be detected in the urine; when only 30 grammes (473 grains), it will not. 6. The urine, normally acid, generally becomes alkaline under the influence of a simple bath. After an alkaline bath, the urine is more commonly acid. 7. The density of the urine is almost always diminished, whether the bath is simple, or impregnated with mineral substances. [Archives Generales, Mai, 1864, p. 543.) - Note to the third edition.