86

ELEMENTS OF MATERIA MEDICA.

ence of any distinct class of agents of this kind. But on the sameground the existence of several other well-established groups or classesof medicines might be denied.

I ought perhaps here to state that, by the term diaphoretic, or sudo-rific, I mean a substance which increases the organic or vital action ofthe cutaneous exhalents. This explanation is necessary, since Dr.Edwards (De Vlnfluence des Agens Physiques sur la Vie, Paris, 1824)has shewn that cutaneous transpiration is effected in two ways ; namely,by a physical action or evaporation, and by an organic action ortransudation. Evaporation, or the physical action, is the consequence ofthe porosity of bodies, and takes place equally in the dead and livingstate. It is influenced by the hygrometric states of the surrounding air,by its motion or stillness, by its pressure, and by its temperature. Thusdryness, agitation, and diminution of the weight of the air, increase it.Transudation, or the organic action of transpiration, being a vital process,depends essentially on causes inherent in the animal economy, althoughit may be influenced to a certain extent by external agents. Thuselevating the temperature of the surrounding air, preventing its frequentrenewal, and covering the patient with warn clothing, are means whichpromote the organic, but check the physical action of transpiration.

The vital activity of the cutaneous exhalents may be promoted in oneor both of two ways,—by increasing the force of the general circulation,or by exciting the cutaneous vessels. Ammonia, violent exercise, andalcohol, operate by increasing vascular action generally, while heatand friction act by exciting the cutaneous vessels. Certain medi-cinal agents, when swallowed, have been supposed to act as diapho-retics, by entering the blood-vessels, and stimulating the cutaneous vesselsby local contact.

The operation of diaphoretics is promoted by the exhibition of largequantities of warm mild diluents, and by keeping the skin warm.Moreover, these agents are more effective when given at bed-time,since there appears to be a greater disposition to sweating during sleepthan in the waking state. The exhibition of diuretics and purgativesshould be avoided, as they check sweating. The older writers explainedthe occasional beneficial effects of sudorifics by supposing that somepeculiar morbific matter was expelled from the system, the retention ofwhich had produced the disease; and hence sudorifics were enumeratedamong the Alexipharmaca and Alexiteria. But though cold, applied tothe skin, may occasion disorder in some internal organ, it is moreconsonant with sound physiology to ascribe the internal affection to ametastasis of vital action, than to the retention of any suppositiousmorbific matter; for although cold diminishes the vital or organicaction of the skin ( transudation ) yet it does not prevent the physicalaction {evaporation).

Sudorifics are employed in a great variety of cases,—as catarrhal andrheumatic affections, febrile disorders, chronic diseases of the skin,&c. They are mostly indicated when the cutaneous transpirationhas been suddenly checked, and some internal part (as the bronchialmembrane) has become affected; also in diseases which usually orfrequently terminate by sweating, as fevers.

2. Errhines (errhina , from iv, in, and piV, the nose) are medicines