(From the same). Diaphoretics. Medicines which promote perspiration. Diaphoretics differ from sudorifics: the former only increase the insensible perspiration; the latter excite a sensible discharge through the skin, which is called sweat. See Sudorifica.
Diaphoretics are those medicines which produce a discharge from the surface; and when this discharge is fluid, they are styled sudorifics. The true diaphoresis is a condensed halitus, distinguishable by a moist clammy feel; while the diapnoe, of which we have had occasion to speak, and to which we shall often return, seems still less sensibly moist, and to be more truly gaseous. This is ascertained by the peculiar softness of the skin in health. These.three states have been supposed to differ only in degree. The insensible halitus, when in a quantity to be condensed, and in this state sensible to the,feelings, is the diaphoresis: and this, when more decidedly fluid, sweat. The same causes, in different degrees, appear to produce each discharge; and they have of course been supposed to proceed from the same vessels, the exhalant arteries. If the distinction were a refinement merely, it would not deserve a moment's notice. We think, however, that it involves many questions of practice. We cannot relieve some complaints without actual sweating, and others are injured by it. Rheumatisms require the former discharge, and fevers demand its regulation, at least, if not the reduction of its violence. Again: diaphoresis, if gradually increased to sweating, can scarcely in any instance be kept up after it. When the sweating is stopped, the skin is dry, and shivering often follows. If, in diaphoresis, we Feel the hand, it is soft and unctuous to the touch: in the most violent sweat, the skin, though covered with moisture, often feels harsh and unyielding in its sub-stance beneath. Sweating almost constantly requires increased heat, or the confinement of the heat of the body. Diaphoresis, on the contrary, is often produced by antimonials and different sedatives. We shall admit that these distinctions may, with a very slight exertion of ingenuity, be reconciled with different degrees of the action of the same vessels; yet, while practical facts lead us to distinguish them in their effects, we were willing to point out some discordance in their phenomena. It is no objection that anatomy does not furnish us with a clue in this investigation, by demonstrating the glandular apparatus. We have no such structure to explain the production of sweat; and the best physiologists consider it as an exhalation from the serous arteries, while others suppose it to be derived from follicles under the skin, though no such have been demonstrated. Sweat, in a chemical view, differs little from the scrum of the blood. It contains, with a large proportion of water, some gluten and muriated ammonia; while the insensible perspiration consists of carbonic acid gas, with a proportion of azotic gas. In some experiments, it has appeared to be chiefly the latter. The acid which occasionally appears on the sweat, is the phosphoric. We have much reason to believe, then, these discharges to proceed from different vessels; and should conclude, that the halitus is a secreted fluid in a gaseous form, while the sweat is only elicited by the force of the circulation from the exhalant arteries. We are confident, however, that these opinions, should they be found or appear fanciful, will not mislead. The distinction which we shall pursue is wholly practical; and, as it was originally suggested by practical facts, we hope it will contribute to elucidate and explain them.
Perspiration has been styled insensible, from its not being cognizable by any sense. Its existence is ascertained by the peculiar softness of the skin, and the general feeling of freedom and hilarity which accompanies this state of health. It is the diapnoe of some authors; but in Chenot, this term rather means a slight degree of diaphoresis. The discharge of insensible perspiration is an halitus not admitting of being condensed in a fluid form, of the nature already explained.
The diaphoresis is an increased discharge of a vapour rather than a gas. It is obvious to our sight, when a sun beam passes over the surface of the body, while naked against a wall, as a slight shade may be perceived. It is usually the effects of warmth, of a stimulus, or of exercise; and is felt by a warm healthy glow, and a sensation of freedom from oppression or inconvenience.
Sweating, on the contrary, is probably a serous discharge from the skin, generally attended with considerable warmth, often with oppressive heat, seldom affording a pleasant sensation, unless associated with mirth and hilarity, as in dancing, or a freedom from pain, as in the sudorific treatment of rheumatism.
These different discharges are excited by different means. The diapnoe is the criterion of health, and we can restore it only by restoring health. Diaphoresis and sweat are excited by different ways, which may be divided into the stimulant and relaxant. The stimulant diaphoretics are chiefly heat, sometimes alone; occasionally assisted by aromatics, and similar heating medicines. We employ sometimes heat alone to produce sweat, as in the sudatoria of the ancients; heat, inother circumstances, is communicated more successfully by vapour and by water, though their relaxant power contributes to the effect: it is communicated also by solid bodies, as bricks or tiles, heated cloths, bottles and jugs containing warm water. The heat of the body itself is sometimes confined for the same purpose, and a partial diaphoresis kept up, by. covering any portion of the body with oil skin;a general sweat by additional clothes, particularly flannel, whose properties we have already explained. See Coopertio.
Heat produces this discharge, when conveyed to the stomach by means of warm water; and it is rendered more effectual when this water is impregnated with different stimuli. The aromatic herbs of our own country, and the spices of the warmer regions, are equally employed for this purpose. Wine, cyder, sometimes beer, ardent spirits, and volatile alkali, arc occasionally added to increase the effect; but these always operate with great stimulus and inconvenient heat.