PHYSIOLOGICAL CLASSES OF MEDICINES.

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different times. It is highly probable that sweat differs from the insen-sible perspiration only in its physical form; and, assuming this view tobe correct, we easily perceive that sweating may be induced in two ways;first, by increasing the cutaneous transpiration; secondly, by altering thehygrometric state of the air, so as to render this fluid less capable o.holding watery vapour in solution. Hence sudorifics and diaphoreticsare not essentially different: the former are generally regarded as beingmore powerful than the latter, or as being the same substances exhibitedin larger doses. This statement, however, is not absolutely correct, inas-much as a diaphoretic may act as a sudorific merely from a change inthe hygrometric state of the air.

The most powerful means of exciting the cutaneous exhalation are,—the external application of heat, and the copious use of diluents. Avariety of solid substances have been used as media for the applicationof heat; as hot sand, bran, ashes, earth, plaster, saline mud, dung,refuse of the grape, &c.

The hot sand bath [arena calida) is a very old remedy. Celsus (lib. i.cap. 17), Dioscorides , and Galen, speak of it. It is a powerfulexcitant, reddening the skin, and producing copious perspiration.Schwilgue [Traite de Matiere Medicate') states that it is used in the mari-time departments of the south of France . The saline mud found on thesea-sliore has been employed in very hot weather, as a bath, by the inha-bitants of Crimea, and especially by the Tartars , against hypochondriasis,scurvy, scrofula, &c. It increases the heat of the body, and excitessweat— [Bull, des Sc. Med. de Ferussac, xiii. 179). Hot dung is some-times used in France , as a kind of bath, against rheumatism, and by tirePoles against syphilis. The’husk of the grape and the refuse of the olive,from which the oil has been drawn, undergo fermentation, and in thisstate have been successfully employed in France against acute rheuma-tism [Diet, de Mat. Med.: art. Bain). Water in a liquid form, or in thestate of vapour and dry air, are also used as media for the application ofheat. Friction, warm clothing, exercise, and cold affusion, are amongthe numerous means that may have been resorted to to produce diapho-resis. Most of the medicinal agents administered for the same purposeare stimulants, and, therefore, the constitutional effects (such as excite-ment of the vascular system, &c.) of the two classes are tire same. Butthe excitement of the system, and the production of sweating, are notalways in the same ratio; and it must be admitted that the sudorificeffects of the compound powder of ipecacuanha and of the antimonialpreparations, considerably exceed their stimulant effects on the systemgenerally.

The agents or means employed to produce diaphoresis are various andeven opposite. In febrile complaints, when the skin is hot and dry, thebest diaphoretics are cooling drinks, acids, and emollients. But inother diseases, when the skin is cold and dry, and there is great prostra-tion of strength, unaccompanied with any local inflammation, diffusiblestimulants (as ammonia) are the best sudorifics. In both of these in-stances the agents employed are relative ; that is, they remove or obviatecauses which impede diaphoresis. As the substances usually deno-minated diaphoretics or sudorifics frequently fail to act as such, that is,to increase perspiration, some writers have been led to doubt the exist-