This section is from the book "A Treatise On Therapeutics, And Pharmacology Or Materia Medica Vol1", by George B. Wood. Also available from Amazon: Part 1 and Part 2.
Hot Vapour Bath. In some countries there are public vapour baths, in which numbers may be collected in the same chamber; and this is occasionally so arranged, with seats rising one above another, that persons may be exposed to various temperatures; the heat of the apartment increasing from below upward, because it is the tendency of the vapour to ascend. Thus, upon the level of the floor the heat may be only 110° Fahr., while in the uppermost part of the chamber it may be as high as 160° or 180°. Of course, the patient inhales the hot moistened air, as well as feels its effects upon the surface. The vapour may be introduced into the chamber from without, or by throwing water, within, upon stones heated to redness by a furnace beneath. But, in this country, it is only the solitary vapour bath which is employed. For the various modes of preparing it, see page 71, in the first part of this work. It may be so arranged that the patient can breathe, at his pleasure, either the moistened air of the bath, or the cold external air. The heating effect of the former is greater; but its revulsive influence is less; and, as it has a tendency to suppress the pulmonary exhalation, it may sometimes act injuriously when the latter would be quite safe.
In consequence of the less conducting power of vapour than of water, the former can be borne at a much higher temperature than the latter; while, for a corresponding reason, the vapour bath may be intolerable at a temperature at which dry air could be borne without inconvenience, the latter being a slower conductor. According to Dr. Forbes, the heating effect of the hot bath, at from 98° to 106°, is equal to that of the vapour bath, when the air is breathed, at from 110° to 130°, and when it is not breathed, at from 120° to 160° (Cyc. of Pract. Med., Am. ed., i. 255); and these are the temperatures within which the methods respectively may be employed; though, in each, the heat may be raised with impunity considerably above the highest point mentioned. The effects of the vapour bath, and of the hot bath, are essentially the same in reference to stimulation and revulsion; but the former is attended with much more copious perspiration during its continuance than the latter; the contact of water with the surface having great effect in preventing extravasation from the blood. Another difference is that the relaxing or sedative effect of the vapour is less than that of the water; and that consequently the stimulation of the former, though more slowly induced, is longer sustained, and is accompanied with a less degree of soothing influence. The vapour bath may be used for the same purposes as the hot bath, but is, upon the whole, less efficient and less agreeable. In its extemporaneous form, it may be employed when circumstances may render it impossible, or extremely inconvenient to prepare and apply the bath of heated water. It is also preferable, in some instances, when the indication is to produce profuse perspiration with a stimulant effect, as in certain cases of chronic rheumatism.
Local vapour baths may be applied by exposing any part of the body to the steam escaping from boiling water, which may be readily confined by a suitable arrangement of woollen or other cloths. But they are employed more for the relief afforded to inflammatory, and other painful affections, by the copious perspiration they induce in the part, than as stimulant agents.
The same may be said of the hot vapour douche, which consists in a jet of heated vapour directed on some part of the surface. It differs from the simple application of steam only in exposing the part to successive portions of vapour, instead of continuously to the same; and the effect is consequently somewhat greater. It may be applied by causing steam to pass through a pipe from a vessel of boiling water; or, in relation to the meatus auditorius of the ear, by holding the orifice of the meatus over the small end of a funnel, the larger end of which is placed over a vessel of water boiling hot. In the latter case, the remedy may be used, as a stimulant to the ear, in cases of defective hearing from deficiency of nervous power.
Finally, healed vapour may be applied exclusively to the lungs by inhalation, and thus made to act as a stimulant to the bronchial tubes when enfeebled, and exposed to the excessive production of mucus in consequence of this relaxed state; but the measure would require to be conducted with much caution. At a lower temperature, so as to produce, not the stimulant effects of heat, but the soothing and emollient effects of mere moisture, it may often be used with benefit But this action of the remedy belongs to another section. For the modes of applying vapour by inhalation, see page 75.
Hot Water as Drink. Hot water has the same stimulant effect, when taken internally, as when applied to the surface; but it is almost never used except as a vehicle for other substances, the action of which it often very much promotes, and, even in this mode of administration, is much less employed with a view to its stimulant action, than as a diaphoretic. In cases of great prostration, it may sometimes be advisable to exhibit stimulant drinks heated rather than cool, as their effects are thus both hastened and augmented.