Having now examined the general nature of baths, and enumerated the most important varieties, we pro ' ceed to describe the effects which they produce on the human body, in its ordinary state of health and vigour ; and to point out how these effects may be ad vantageously employed in the prevention or the cure of disease.
The effects of bathing will depend, partly on the quality and composition of the water employed, and partly on the quantity and mode of application ; but more especially on the temperature of the bath.
Immersion even in simple water, of such a tempe rature as to affect the body with no striking sensa tion either of heat or cold, * is attended with seve ral advantages. The surface of the skin is freed from that scaly sorties, which always collects more or less in the healthiest persons ; and hence the pores of the skin are opened and relaxed, and the natural perspi ration is promoted ; the limbs are rendered supple, and any stiffness which may have been produced by great exertion or fatigue is removed. Such an immersion has also been found to alleviate thirst ; a clear proof, in the opinion of most physiologists, that a quantity of the water is absorbed, or enters through the skim into the circulation.
If, instead of immersion in tepid water, affusion be employed, the general result is much the same, ex cept that, if the body continue exposed to the air after the affusion, a sensation of coldness is produced, and this in proportion as the air is more favourable to evaporation, and, consequently, to the generation of cold on the moistened surface.
When water of the same medium temperature, but impregnated with some mineral substance, is employ ed, it is generally supposed, that the impregnating matters produce on the system effects, similar to those which would follow their internal exhibition. . That this is the case in some instances we shall not deny, but, in most cases, the effect is very trifling, and in some scarcely perceptible. Immersion in sulphureous tepid waters commonly produces an increased perspi ration ; and a similar use of chalybeate waters, espe cially if these contain any aluminous impregnation, is followed by a corrugation of the skin, and an increa sed action of the vessels. These effects we can rea dily explain, from the absorption of the sulphureous gas in the former instance, and the corrugating effect of the alum and chalybeate acting as an astringent on the skin, and thus producing pressure, and conse quent contraction, or acceleration of the fluids, in the vessels near the surface ; but that alkaline, or earthy salts, should produce any remarkable effect when ap plied in solution in the way of bathing, is not to be expected, as these salts cannot, we conceive, thus enter the absorbents of the skin. Indeed, that they are
not absorbed, is evident from the circumstance, that even sea-water will allay thirst, merely by wetting with it the surface of the body. We are therefore disposed to think, that the advantages of sea-water over fresh, as a bath, used rather for health than for exercise and recreation, have been much exaggerated. In some cases, the salt may certainly act as a gentle stimulus on the surface ; and this effect will be in creased by heat, friction, or a long immersion ; but ih cases where the immersion is only momentary, or where affusion is employed, and where the body is im mediately dried, salt water can little more ad vantage than that of convenience.
In describing the effects and uses of baths of diffe rent temperatures, we shall begin with the cold bath, whose temperature does not exceed 65°, as that. which has, in this country, been most universally, em ployed.
When a person, in the ordinary state of health, is immersed in the cold bath, he first experiences a ge neral sensation of cold, which is almost succeeded by as general a sensation. of warmth ; the, latter rapidly increasing, so as to cause the surround ' ing water to feel of an agreeable temperature. If the immersion have been sudden and momentary, and the body be immediately dried and covered from the air, the sensation of warmth continues, the whole body feels refreshed and invigorated, and, under favourable circumstances; the natural perspiration is increased. If, however, the immersion be continued for a considerable time, and the water he not near the highest range of the temperature which we have as signed to the cold bath, the sensation of warmth goes off, and is followed by numbness and shivering ; the skin becomes pale and contracted ; the vessels near the surface are evidently diminished in diameter, and their contents are either lessened in volume, or pro pelled with greater force towards the internal parts. The person feels drowsy and inactive ; his joints be come rigid and inflexihle ; his limbs are affected with pains and cramps ; his respiration becomes quick and irregular ; his pulse slow and small, but for a time firm and regular ; his perspiration is suppressed ; and generally a copious discharge of urine takes place. If the immersion be still continued, or if the water be very cold, the pulse gradually ceases at the wrist ; the action of the heart becomes weak and languid ; a sensation of faintness and coldness of the stomach is experienced, followed by a rapid diminution of the whole animal heat. At length delirium and torpor come on, and the person is carried off by a fatal apo plexy.