Next to the alimentary canal, the skin is most frequently resorted to for the application of medicines. The object may be either to affect the system or some unconnected part through absorption, sympathy, depletion, revulsion, etc., or to act exclusively on the skin itself. The modes of application are various, both in relation to the state of the skin and the substance employed. Thus, the skin may remain undisturbed, the medicine being merely brought into contact with it; or the epidermic scales may be disturbed by friction at the time of application; or the epidermis may be removed, and the medicine placed upon the denuded cutis. The substance employed may be solid, semiliquid, liquid, or aeriform, and, if solid, may be of different degrees of consistence.

1. Simple Application to the Sound Skin

Of such application we have examples, with reference to solids, in cataplasms, cerates, and plasters; with reference to liquids, in lotions, fomentations, general baths, local baths, the douche, affusion, and sponging; and, with reference to aeriform substances, in the hot air bath, the general and local vapour bath, and the vapour douche. Of the different solid forms mentioned, as well as of lotions, enough has been already said. Fomentations or stoups are heated liquids, applied by means of flannels or other cloths saturated with, or wrung out of them. They are usually employed to obtain the effects of water and heat, but sometimes also for the specific effects of medicines, as when the decoction of poppy-heads, or infusion of tobacco is applied.

Baths consist in the direct application of water, either pure or medicinally impregnated, more or less extensively to the surface; the general hath being applied to the whole surface, the head perhaps excepted; the semicupium or half-bath, to the lower half of the body; the coxaeluviuvi or hip-bath, to the pelvis and upper part of the thighs; the pediluvium or foot-bath, to the feet and legs; and the maniluvium or hand-bath, to the hands and forearms.* When the water is made to fall upon the body generally from above, in minute currents or streams, as through a colander, the application is called a shower bath; when a single stream of greater or less size is directed upon one part with more or less force, it is named, from the French, the douche. In all these, the water may be cold, warm, or hot; and we thus have the cold bath, the warm bath, and the hot bath, which are very different in their effects, and employed for a great diversity of purposes. Of the principles of operation, and of the applications of the different forms of baths, I shall have occasion to treat. at some length, under the different classes of remedies to which they respectively belong. It is sufficient here to state that the bath, when below 75°, may be called a cold bath.; when between 85° and 98°, a warm bath : and from 98° to 112°, a hot bath. Some make a distinction between the tepid and warm baths, the former being of a somewhat lower temperature than the latter.

* The means of employing the varieties of local bathing mentioned in the text are well known; but the application of water to other limited parts than those referred to may be indicated, and some ingenuity would be requisite to fashion apparatus suitable for the purpose. The reader may find it useful to consult, upon this subject, a paper on the "Localization of Baths" by Dr. Conrad Mayor, contained in the New York Journal of Medicine (3d ser., ii. 182). - Note to the second edition.

Water may also be applied to the surface more or less extensively by means of wet sheets, or cloths, which may be wrapped around the whole body, so as to obtain in some degree the effect of the general bath, or folded and applied around the waist like a belt, with a view to local effect.

The douche acts not only by the temperature of the water, but also by the shock and pressure, consequent upon the force with which the liquid falls. When continued long, or from a considerable height, say ten or twelve feet, it becomes after a time extremely painful, so as to be quite intolerable; and, on this account, has been employed as an instrument of fear or punishment to criminals and maniacs. So far as it acts mechanically, it is primarily excitant, and secondarily depressing.

Liquid in the form of spray, or pulverized by minute division in a current of air, has been of late used in the mode of a douche, and produces analogous, but milder effects. Independently of the mechanical results of percussion, and the peculiar local effects of the medicine, it is asserted that substances applied to the surface in this way are sometimes absorbed, and act characteristically on the system. Directed to the conjunctiva, they are said to enter the lachrymal passages and even to reach the nostrils. (Archives Gen., Juin, 1866, p. 725.) When the liquid employed is very volatile, an intense degree of cold may be produced by its rapid volatilization, which has recently been applied to important practical purposes, as will be more fully stated hereafter.

Affusion consists in the pouring of water, at various temperatures, from pitchers, buckets, etc., more or less extensively over the body. It differs from the douche in being more diffused, and in falling with less force upon the surface. It has been highly recommended in certain febrile and inflammatory diseases, but requires caution in its use. of which more will be said hereafter.

Sponging is a term sufficiently expressive without definition. It may be employed locally or generally, with water, spirit, or other liquid, at different temperatures. It is often extremely useful.

Heated atmospheric air has been employed as a remedial agent, in the form of a warm or hot air bath. When the object is that the patient shall breathe the heated air, as well as experience its effects externally, it may be most conveniently accomplished by simply placing him naked in a confined apartment, raised by the introduction of hot air to the required temperature, which may vary from 90° to 150°. More frequently the application is made to the external surface alone, while the patient is allowed to breathe air at ordinary temperatures. This may be done by inclosing the body in a cell, box, or closet of suitable dimensions-arranged that the head shall project through an opening, which is accurately closed around the neck, while the confined air is heated by any convenient plan. An extemporaneous bath of this kind may be prepared, by supporting the bed-coverings, over the patient in bed, upon two or three pairs of crossed half-hoops, so as to form a vacant space around him; and then either introducing heated air, by means of a tube. from some exterior source, or heating that around the patient by hot bricks, bottles filled with hot water, or bags filled with heated salt, oats, or other suitable material.

Medicated hot air baths may be applied, in the same way, by impregnating the air with gaseous bodies, as chlorine and sulphurous acid, or with the vapours of volatile solids, as cinnabar, iodine, etc.

The vapour bath, like the hot air bath, may be so employed that the patient shall or shall not breathe the vapour. In the former case, the heating effect upon the body is greater from a certain temperature of the bath than in the latter; for the natural refrigerating effect of the pulmonary exhalation is prevented. The bath is much more frequently employed in reference to the external surface alone. Various modes of obtaining the effects of the vapour bath have been practised. One of the most simple is to make a space around the patient in bed, by elevating the coverings by means of crossed half-hoops, in the manner above mentioned, and tucking them well in at the sides of the bed or mattress, and then to introduce into this space bricks previously heated, immersed in water, and covered with flannel, taking care that they do not touch the body of the patient. The vapour from* the heated bricks soon fills the empty space. Another mode of introducing vapour is by means of Jennings' apparatus, which consists of a tin tube, much broader at one extremity than the other, curved so that the smaller end may be inserted into the space around the patient, while the larger end may be supported on a stool without the bed. A lighted spirit lamp is placed within the broad end of the tube in the side of which an opening is left for the entrance of air. As the spirit burns, a current of heated air, with the aqueous vapour and carbonic acid resulting from the combustion, passes through the tube, and envelopes the body. A different mode of accomplishing the same end, is to seat the patient on a stool or in a chair, placed either over or in a tub or bucket containing hot water, and then, by blankets descending from his shoulders to the floor, to enclose together his body and the whole apparatus. The heat of the water may be increased by introducing into the tub or bucket heated bricks, as they may be required. Caution, however, is requisite not to scald the patient. A case occurred in Philadelphia, under the care of an empiric, in which a child, subjected to a vapour bath of this kind, was scalded to death.

Where convenience permits, a better vapour bath may be arranged, by making a frame of wood-work, and covering this with cloth impervious to vapour, so as to enclose a space within which the patient may conveniently sit upon a stool or chair, while the vapour is introduced into the lower part of the enclosure, by means of a tube proceeding from a kettle of boiling water. The heat of the vapour may vary from 100° to 150°, and has been increased with impunity beyond the latter temperature; but it is better, in this respect, to err on the side of caution.

Medicated vapour baths may be formed by introducing volatile substances into the water evaporated, so that their vapour may rise with that of the water.

The vapour douche is a stream of vapour directed with some force upon a particular part of the body.