This term is applied to a metallic body, heated sufficiently to enable it to destroy the life of the part with which it may be brought into contact. iron or steel is usually employed. The metallic instrument used is of various forms; but consists generally of a long stem, which serves for a handle, and of a thicker terminal expansion, which is the part heated. The latter is of different shapes to meet special purposes, conical with the point truncated, flat and circular or oval, hexagonal, etc. it may be heated to the temperature of boiling water, to dull redness, to full redness, or to whiteness or incandescence.

The actual cautery has been used for most, if not for all the purposes of escharotics in general, and for some to which the other articles of the class are less applicable or quite inadequate; as for arresting hemorrhage in parts where the ligature cannot be applied, and ordinary styptics have proved unavailing, for cauterizing indolent carious ulcers in deep-lying bones, and for destroying tumours in parts inaccessible to the knife, as in the antrum. It has also been particularly recommended in callous fistulous sores, and poisoned wounds; and is said by M. Guer-sant to be the most efficient agent in the cure of prolapsus of the rectum. (Gaz. des Hop., No. xiii.) Even in the formation of issues and ulcerated surfaces, its advocates claim for it a superiority over caustic potassa, on the grounds that its pain, though severe for an instant, is of shorter duration, that the slough separates more speedily, leaving a stronger disposition to copious suppuration behind it, and that, as it destroys the parts which it touches, and only these, it is easier to regulate the precise limits of the escharotic effect. The heat radiating through the surrounding tissues sets up in them an inflammatory excitement, which both produces the local effects just referred to, and brings the system into a sympathy, which may sometimes be beneficial.

For producing a considerable or deep slough, the instrument should be at a white heat or incandescent, should be applied With some force to the part, and should not be allowed to remain in contact with it longer than 7 or 8 seconds at furthest. Should more effect than is thus produced be required, the first instrument should be immediately followed by a second, and this sometimes by a third. To protect the neighbouring parts, they may be covered by a thick compress or piece of pasteboard, previously steeped in a solution of common salt. It is generally advisable to make an incision in the skin with a bistoury, before the application of the instrument, in order to produce a deeper impression. (Mar-jolin et Ollivier, Diet, de Med., vii. 53.)

In producing mere superficial ulcers, the truncated point or edge of the instrument, now only at full redness, may be drawn rapidly and lightly in parallel lines over the surface; and the same operation may be repeated, if the first effect should not be sufficient. Inflammation with swelling occurs, the sloughs spread and separate, profuse suppuration takes place, and the parts heal in two or three weeks, leaving slight cicatrices, which are ultimately nearly obliterated. This remedy, which is called transcurrent cauterization by the French, has been strongly recommended in obstinate chronic inflammation of the larger joints, of a rheumatic or scrofulous character, in chronic synovitis, and in neuralgic affections. (Ibid.) M. Faure advises it also in asphyxia; the application being made to the upper and lateral part of the chest. (Med. Times and Gaz., Dec. 1855, p. 628.)

Another method of superficial cauterization is by means of metallic plates, of a size corresponding with the extent of effect desired, which are introduced for five minutes into boiling water, or salt water, which boils at a higher temperature, and having thus acquired the heat of the vol. ii.-50 liquid, arc applied with pressure to the surface for a period of about ten seconds. This time is usually sufficient to secure a superficial slough. The same instrument may be used for vesicating, by covering the surface with a piece of dry silk, previously to the application of the heated plate. Rubefaction is thus produced, which is in a short time followed by a blister. if it be desired simply to redden without vesicating, the period of application must be only momentary.