(From to bring on crusts by burning, ultimately from uro). Escharotics, called also erodentia, caustica, cauteria. Substances which dissolve the solid matter of the human body, or attract its moisture. They are used where either a portion of the solid matter is to be taken away, or its texture to be so destroyed that it may fall off, or be easily separated from the other parts.

Caustica, (from uro, to burr:,) caustics, and escharotics differ only in degree, for both destroy the part to which they are applied. Van Helmont first asserted their inefficacy on dead bodies: and Dr. Petit of Paris confirmed it. These kind of applications deprive the part of life, either by their attraction for moisture,. which destroys the organization, or by excess of excitement. The dead portion is then separated by the vital power; and what surgeons call the slough, or es-char, is separated.

Caustics, or cauteries - for they do not differ-are distinguished into actual and potential. The actual is real fire, or a red-hot iron; but these, on account of the terror and pain they occasion, arc laid aside. The potential are those which act in the manner already explained. The. chief of these are what were called causticum lunare; commune fortius, or lapis infernalis-; antimoniale: now named argentum nitratum; calx i kali puro; antimonium muriatum.

Their use, besides that of destroying excrescences, or morbid parts, is to open large abscesses where there is danger of cutting some adjacent vessel, or when the knife terrifies the patient. In this case the common milder caustic is generally sufficient, and may be thus applied: lay a piece of sticking plaster on the soft part, of the abscess, having previously cut a hole in it, nearly as big as the eschar is to be made; on the hole of the plaster lay the caustic, which must be secured by another piece of sticking plaster. When the skin is not inflamed, the caustic very often occasions little or no pain; and when the eschar separates, or is so loose as to be easily removed, the purulent matter is discharged. When issues are made by caustics, or bones laid bare by them, the eschar must be cut out immediately, or very soon, lest new flesh should fill up the part which is opened. To lay a bone bare, or to make an issue, let the caustic continue on the part about four hours; to destroy a large gland, six; but to open an abscess it may remain two or three hours, according to the thickness of the skin; though generally, when the effect of the caustic is completed, the part on which it is applied ceases to be uneasy.

When a large fungus is to be destroyed by a caustic, the method described by Dr. Barry in the Edinburgh 4 L 2

Medical Essays seems most eligible. The lapis infer-nalis was applied to a tumour on the coats of the testis; after the separation of the eschar, the lapis infernalis and oleum vitrioli were alternately rubbed on the part; the one instantly removing the pain occasioned by the other: at each dressing, this alternate application was repeated, till the intended effect was produced: the moisture was then absorbed by an armed probe, and a digestive applied. This method prevents the continuance of pain, and is not productive of any degree of inflammation; it is also recommended for the removal of scirrhus, or any other tumour that admits of a caustic; but it very often fails.

Mr. John Hunter recommends a mixture of opium with caustics, in order to lessen the pain which they occasion: this plan generally succeeds, though a much longer time is necessary. See Causticum opiatum.

A great inconvenience in the application of caustics is their spreading, when applied, beyond their limits. The solid form of the argentum nitratum is in this way very convenient. Applications which destroy tender fungous flesh are of this kind, as the vitriolated copper, the red oxides of mercury, and alum, so far calcined as to separate its water and concentrate its acid. All the mineral acids are caustics; but seldom used on account of their great fluidity. See White's Surgery, p. 188.