1. Diaphoretics are often useful by relieving the heat and dryness of the surface, which are so common in febrile diseases, whether idiopathic or symptomatic, and which operate injuriously upon the disease by an irritant reaction on the system. Upon this principle alone, were there no other ground for their use, they would prove beneficial in all cases of fever with, a hot, dry skin.

2. They deplete from the blood-vessels, and sometimes very copiously. It is not only the watery parts of the blood that are carried off under their influence, but the salts, and, to a certain extent, the organic constituents also. Hence, copious sweating is very debilitating. Every one knows how exhausting to the strength are the night-sweats of hectic and of convalescence. From this effect of diaphoretics, they may often be serviceably employed in inflammatory and febrile diseases, in which the blood is too rich, and the general condition of the system sthenic.

3. Diaphoretics promote absorption by their depletory influence, and on this principle are sometimes used very happily in dropsy. I have known severe dropsy to yield to this class of medicines, after diuretics had been employed without effect.

4. They act revulsively towards the surface of the body from the interior organs. in this way, they are useful in all the interior inflammations and vascular irritations; but are especially efficacious in inflammatory conditions of the mucous and serous tissues, as in bronchitis, enteritis, dysentery, peritonitis, etc. it is probably upon this principle, partly, that they act favourably in the different forms of rheumatism. in morbid diuresis and in diarrhoea, they also act favourably by diversion to the surface, and substituting one discharge for another. in eruptive affections, whether febrile or not, diaphoretics sometimes serve an excellent purpose, upon this principle of derivation, by inviting a retarded or repelled eruption to the surface, and thus relieving internal irritation.

5. They eliminate noxious matters from the blood, and may often possibly operate usefully in this way, when given to meet other indications. Little, however, is known with certainty on this point. it is probable that they act usefully upon this depurating principle, in gout, rheumatism, and various idiopathic fevers. in calculous affections, also, when acid in the circulation may dispose to deposition of uric acid in the urine, it is possible that diaphoretics may prove useful, by eliminating the offending matter through the skin.

6. Certain diseases show a tendency to pass off with copious sweating. it has been thought that nature might be advantageously imitated by the use of diaphoretics, and an earlier solution of the disease thus obtained, than if it were left to its ordinary course. There is probably some ground for this supposition. in miasmatic fevers, I have little doubt that We may thus often lessen the duration, and effect a more complete solution of the paroxysms; converting an almost continuous fever into a distinct remittent, a remittent into an intermittent, and a doubtful intermittent, with long paroxysms, into one in which the apy-rexia is more complete, and the paroxysms shorter.

7. it sometimes happens that the skin falls into an inactive or torpid state, and ceases to perform its function properly; in consequence of which, the blood may become impure, and various internal irritations, whether of a vascular or nervous character, may arise. There is here an obvious indication for the use of diaphoretics, and especially those of a somewhat stimulating character. it is in this way, probably, in part, that the stimulating diaphoretics prove useful in chronic rheumatism, scrofula, secondary syphilis, and other cachectic conditions of the system.

3. Administration

if copious perspiration be desired, the patient should be confined to bed, and clothed with light flannel or other woollen tissue next the skin, or placed between woollen blankets. The reason for this is that wool, on account of its slow power of conduction, prevents the rapid escape of heat, and obviates danger from accidental exposure of the surface, and premature checking of the perspiration.

if the pulse be full and strong, and the general excitement considerable, it will usually be advisable to precede the diaphoretic by measures calculated to diminish plethora, and reduce action, so as both to favour the absorption of the medicine, and to bring the cutaneous excitation down to the secreting point. For this purpose, the appropriate measures are bleeding, when called for also by other considerations, the saline purgatives, the antimonials with a view to their sedative influence, and a low diet.

if it be desired that the diaphoretic should act profusely, it ought to be accompanied with warm diluent drinks, as balm tea, hot lemonade, hot molasses and water, etc., or some one of the gently stimulating infusions already mentioned {page 652).

During the continuance of the diaphoresis, purgation and diuresis should, as a general rule, be avoided, and, if existing, should be suppressed by appropriate measures, as by warmth in reference to the latter, and by opiates in reference to both.