Perspiration, in animal economy, signifies the exhalation of humours through the pores of the skin. It is cither sensible, that is, sweat ; or insensible, namely, such as cannot be perceived. In the latter sense, the term perspiration is generally understood when used alone; and in this signification we shall briefly consider the subject.

Insensible perspiration is the most important of the natural evacuations, by which all thin and acrid humours are carried off, and the body is cleared from impurities. This function is most active during the night; and it is computed, that healthy individuals perspire from three to four, or five pounds weight in the course of twenty-four hours. Hence the body feels more lively and vigorous when transpiration is uniformly effected; but, if it be obstructed, or become irregular from any cause or accident, the whole system will be disordered ; so that head-achs, torpor in the limbs, and a variety of other complaints, are the consequence.

This salutary discharge, however, is very unequal in its operation, at different times. Thus, after a full meal, we perspire with less energy ; but, when digestion is completed, both the circulation of the blood, and the action of the pores, receive additional vigour from the conversion of chyle into blood; so that perspiration is renewed with greater activity.

As numerous disorders originate from frequent irregularities in this most important function, the greatest caution is necessary to promote its activity. Hence all, who have any regard for their health, ought to fortify themselves against the sudden changes of our variable climate, especially by taking moderate exercise in the open air, every day; to avoid colds, or catarrhs, by guarding against wet clothes, or damp feet; as the moisture, when absorbed by the body, augments the danger arising from such imprudence. Persons thus situated, ought instantly to change their clothes, and not to sit or lie down, while they are wet; but, as many are prevented from availing themselves of this precaution, in such cases brisk exercise should betake 1, till their dress become perfectly dry. In this manner, colics, inflammations of the bowels, rheu-matisms, and a variety of disorders, both acute and chronic, may be effectually obviated : for no constitution, however robust, can resist the hurtful effects arising from wet clothes.

Where perspiration is already obstructed, we would advise the patient to take moderate exercise ; to bathe his feet in tepid water; and to employ mild sudorific remedies, when retiring to bed ; such as a glass of cold water, if the be of a vigorous habit; or otherwise, a few cups of luke-warm tea ; or white-wine whey, without spices ; but never to indulge in the free use of spirituous mixtures. These, indeed, may prove a temporary stimulus to the body, and increase the circulation of the blood which had been impeded ; yet, eventually, they will be productive of more injury than benefit ; and thus imperceptibly induce the most detestable of habits.—See also Chronical Diseases, vol. i. p.