As different theories have dictated, we have been sometimes alarmed with apprehensions of producing morbid viscidity and lentorof the fluids by sweating; at others, taught to promote this evacuation to counteract preternatural tenuity. Each danger is equally imaginary. When sweat is excited, other watery discharges are proportionally diminished, and thirst leads the patient to require a supply. On the other hand, tenuity of the blood, when it exists merely in consequence of an increased proportion of water, is relieved by the kidneys, without any effort on our side. When it arises from an increase of the ammoniacal salts in the blood, the debility which attends prevents the use of remedies which, in any degree, weaken the system. In those cases where acrimony may be suspected, (they are indeed very rare,) violent, insatiable thirst calls for a supply of watery fluids for their solution and evacuation. They are then eliminated through the urinary organs. We must next consider the diseases to which diaphoretics are applicable.

The insensible diapnoe, we have said, is the criterion of health, and can be produced only by supporting the general healthy state. It is most observable in cold weather: and the nearer we approach to it in every disorder, the greater is our success. It is generally obtained by free cold air, when this is admissible; and to attain it is our aim in every complaint.

The moderate diaphoresis is our chief object in the greater number of acute diseases. To begin, as usual, with the pyrexiae, we may remark, that diaphoretics are, in this class, of very extensive utility. Intermit-tents are usually left to their course during the paroxysm, and the efforts of the physician are reserved for the interval. Yet there are circumstances in which the return of the paroxysm would be fatal; and others, where the delirium, in the hot fit, is most alarming. In each case, diaphoretics arc employed: in the first, to support the circulation in the extreme vessels, that the fit may be obviated; in the second, to hasten the natural crisis by perspiration. The kind of diaphoretics chosen for the first purpose, is the warm stimulants; the reason of which we shall afterwards explain. To assist in promoting perspiration, in the hot fit, the relaxants, and particularly opium, are preferred. This was the practice introduced by Dr. Lind.

In continued fevers, it was, for ages, the custom to give the most stimulating diaphoretics to promote the concoction of morbid matter. Not a breath of air was suffered to approach the patient; but serpentary, contrayerva, and volatile alkali, were exhibited in profusion.

have been assured, that three beds have, in succession, rotted by the sweat, under the same person, in a single fever. We still attempt to promote perspiration; but by cooling, rather than heating, remedies, adapting them to the circumstances and to the temperature of the patient. Modern practice has freely adopted the relaxant diaphoretics, particularly the antimonials, to conquer the supposed spasm on the surface. We trust that we shall show that this plan has at least been carried to an improper extent, even if it appear well founded in its principle.

In the phlegmasia the skin is hot and dry, and the utility of diaphoretics is obvious. As the temperature of the skin is above the sweating point, cold is chiefly-indicated; yet, in many of the diseases, this plan cannot, for reasons already assigned, be carried to a considerable extent (see Cold). We must, therefore, adopt the relaxant diaphoretics; and of these we are often obliged, for other reasons, to avoid opium. Antimonials are then our chief dependence, with the other remedies peculiarly adapted to the seat of the complaint. There is, however, one disease, which is an exception to these general remarks; rheumatism. After the more active period of the complaint, it admits of the more stimulating diaphoretics; and when the fever has abated, of the most stimulating. In fact, after a time the vessels become torpid and paralytic, to be roused only by the most powerful exciting causes; but this state can only be explained under the proper head, after many previous distinctions. See Inflammatio and Rheumatismus.

In the hemorrhagic we find little room for diaphoretics, except of the most cooling kind. The source of their utility in relieving internal congestions has been already explained; but it will be obvious that these remedies are chiefly of service in active haemorrhages, where the heat is preternaturally increased. In this case, cold drinks and cold applications are, as usual, the most powerful diaphoretics. In the passive haemorr-hages they relax too powerfully to be of the slightest utility. In reality, they are highly injurious. Exanthemata. The diseases of this order peculiarly require the use of diaphoretics; but, in the greater number of genera, the heat is already beyond the point which admits of a discharge from the skin, so that the more cooling medicines of this class are preferred, ex-cept in one genus, the measles. In scarlatina, the cold affusions, long continued, have been found of singular utility in promoting perspiration. In the plague, the gentle diaphoresis called by Chenot the diapnoe, is found of the greatest utility; and it appears probable, from the late experience in this complaint, that this is best obtained by cold. To this general doctrine there are only two exceptions, either when the disease is of a putrid nature, or the eruption has disappeared. In these cases warmth of every kind is essentially necessary, and warmer diaphoretics are only employed. In the prqfluvia, this class of remedies is of the highest importance. In the only two diseases included under it in the best system of nosology, diaphoretics chiefly relieve. In catarrh, their use is well known; and in dysentery, when purgatives have evacuated the accustomed scybala from the intestines, the ipecacuanha and antimonials, so universally recommended, undoubt-act only by determining to the surface.

In the first order of the neuroses, the comata, diaphoretics are not peculiarly indicated. Yet we must keep in our view the advantages which, in every case of internal congestion, arise from keeping the extreme vessels in an active state, since they contain so considerable a portion of the fluids. Of the adynamia, dys-fiefisia, hypochondriasis, and chlorosis, require the same attention. In each there is always a defect of perspiration; and, in each, to restore it, contributes greatly to the patient's relief.

Of the spasmi, tetanus chiefly demands our attention to the state of the skin, as it often proceeds from cold, and is relieved by active sweating. When mercurials, with opiates are of such singular service, the benefit probably originates from the same source. In asthma, the utility of diaphoretics is sufficiently obvious, from what we have already said; and in colic and diarrhea external warmth is singularly useful. In cholera they are of peculiar service; and Sydenham has remarked, that every remedy to calm the vomiting has failed, till a sweat broke out. We mention this more particularly, as the advantages of these remedies were not duly enforced under the proper head.

Of the vesaniae, melancholia alone seems to be parti-ticularly relieved by diaphoretics; yet, in those cases of mania where there is great internal congestion, could the patient be properly confined, they might be useful. In the cachexiae we see little foundation for their peculiar employment. In each genus, however, the circulation in the extremities is particularly languid, and the external stimulating diaphoretics are of use. Of the impetigenes, the diseases merely cutaneous are benefited by them; but these require the more gently stimulating kind, which act steadily rather than violently: we mean the mercurials, the sarsa, the mezereon, and the others enumerated.

The chief disadvantages of diaphoretics arise from their debilitating effects. The discharge, therefore, in every instance, should be conducted with caution and moderation; nor should the practitioner aim at relieving his patient rapidly, when the cure would be safer and more permanent, were the course more gentle and steady; and when the perspiration has been kept up with violence, relapses are by no means uncommon.