air at 75 is perhaps too warm for the feelings of many people, a continued bath at that temperature is felt to be cold and depressing. Again, a bath of 98 to 102 acts far more excitingly than air of the same temperature, both because, being a better conductor, water brings more heat to the body, and because it suppresses the perspiration, which is greatly augmented by air of that temperature. Further, a temperature a few degrees below blood heat is that of indifferent baths, which can be borne longest
without natural disturbance of the system.
Cold baths act by refrigeration, and their effects vary according to the degree of temperature. The effects of a cold bath, the temperature not being below 50, are these : there is a diminution of the temperature of the skin and of the subjacent tissues; the blood at first rises in temperature nearly 4, but soon subsides again, this diminution of temperature of the blood usually not taking place in the bath, but shortly after leaving it. There is a certain feeling of shock diffused over the whole surface, and if the cold is intense it induces a slight feeling of numbness in the skin. It becomes pale and its capillaries contract. The further action of a cold bath reaches the central nervous system, the heart and the lungs, as manifested by the tremor of the limbs it produces, along with a certain degree of oppression of the chest and a gasping for air, while the pulse becomes small and sinks. After a time reaction takes place, and brings redness to the skin and an increase of temperature.
The colder the water is, and the more powerful and depressing its effects, the quicker and more" active is the reaction. Very cold baths, anything below 50, cannot bo borne long. Lowering of the temperature of the skin may be borne down to 9, but a further reduction may prove fatal. The diminution of temperature is much more rapid when the water is in motion, or when the bather moves about ; because, if the water is still, the layer of it in immediate contact with the body gets warmed to a certain dsgree.
The effects of hydropathy depend on the power of abstracting heat from the body, and of stimulating it by the application of cold water. The action is depressing or exciting, according as the withdrawal of heat or the stimu lation predominates.
A great deal depends on the form of the bath ; thus one may have (1.) Its depressing operation, with a loss of heat, retardation of the circulation, and feeling of weari ness, when the same water remains in contact with the skin, and there is continuous withdrawal of heat without fresh stimulation. This occurs with full or sitz baths, with partial or complete wrapping up the body in a wet sheet which remains unchanged, and with frictions practised without removing the wet sheets. (2.) Its exciting operation, with quickening of the action of the heart and lungs, and feeling of glow and of nervous excitement and of increased muscular power. These sensations are produced when the layer of water next the body and heated by it is removed, and fresh cold water causes fresh stimulus. These effects are produced by full baths with the water in motion used only for a short time, by frictions when the wet sheet is removed from the body, by douches, shower baths, bathing in rivers, &c. ..The depressing operation comes on much earlier in very cold water than in warmer ; and in the same way the exciting operation comes on faster with the colder than with the warmer water. The short duration of the bath makes both its depressing and its exciting action less ; its longer duration increases them ; and if the baths be con tinued too long, the protracted abstraction of animal beat may prove very depressing.
We shall not attempt to give more than those few hints about hydropathic processes, and shall merely remark that, under them the system is subjected to alternate periods of excitement and of rest. There is persistent lowering of the temperature of the body, with contraction of the capillaries and local amemia. This is succeeded by the reverse, or by local hyperamiia. There is powerful excite ment of the vascular and nervous systems. The processes of absorption and of excretion are stimulated. There is a great increase of perspiration. The transformation of tissue is materially quickened.
We must next consider the operation of warm baths of different temperatures.
Tepid, 85° to 95°.—The effects of a bath of this tem perature are confined to the peripheral extremities of the nerves, and are so slight that they do not reach the central system. There is no reaction, and the animal temperature remains unchanged. Baths of this kind can be borne for hours with impunity.
Warm baths from 96° to 104°.—In these the action of the heat on the peripheral surface is propagated to the central system, and causes reaction, which manifests itself in moderately increased flow of the circulating fluids to the surface, and in an increased frequency of pulse. It appears to supply a slight stimulus to the renewal of tissue.
With a hot bath from 102° up to 110° the central nervous and circulating systems are more affected. The frequency of the pulse increases rapidly, the respiration becomes quickened, and is interrupted by deep inspirations. The skin is congested, and the retained animal heat bursts out, causing a profuse perspiration.
Very hot bath.—Everything above 110 feels very hot ; anything above 120 almost scalding. Baths of from 119 to 126 have caused a rise of 2 to 4 in the temperature of the blood. Such a bath can only be borne for a few minutes. It causes violent reflex action on the heart and the arterial system, excessive congestion of the skin, and violent perspiration.
In the use of hot baths a certain amount of vapour reaches the parts of the body not covered, by the water, and is also inhaled.
Vapour baths produce profuse perspiration, and act in cleansing the skin, as powerful hot water baths do. Vapour, owing to its smaller specific heat, does not act so fast as water on the body. A vapour bath can be borne for a much longer time when the vapour is not inhaled. Vapour baths can be borne hotter than water baths, but can not be continued so long, as vapour, being a bad con ductor, prevents radiation of heat from the body. A higher heat than 122 is not borne comfortably. The vapour bath, though falling considerably short of the temperature of the hot air bath, heats the blood considerably more.
Hot air baths differ from vapour baths in not impeding the respiration as the latter do, by depositing moisture in the bronchial tubes. The lungs, instead of having to heat the inspired air, are subjected to a temperature above their own. Hot air baths, say of 135, produce more profuse perspiration than vapour baths. If very hot, they raise the temperature of the body by several degrees.
Vapour baths, hot air baths, and many hydropathic processes agree in producing violent sudation, and also fre quently in subjecting the body, while in a state of perspiration, to the action of water of a comparatively low temperature. Of perspiration we shall only say, that it is sensible and insensible : 30 oz. may be considered to be about its average amount in the twenty-four hours ; of this, which is chiefly water, about
