These are agents which, applied to any portion of the body, destroy the life of the part with which they are in contact, and produce a slough.

They operate either dynamically, by an influence directly on the vitality of the part, or chemically, by decomposing the tissues affected. in the former case, they produce disorganization by first destroying life; in the latter, they destroy life by producing disorganization.

They are employed 1. to form issues; 2. to produce superficial ulceration and suppuration; 3. to alter the action of diseased surfaces, by removing a layer of the tissue in which it is seated; 4. to promote the healing of ulcers, by forming a covering impervious to the air; 5. to remove fungous granulations, and other morbid growths, as carcinomatous tumours, etc.; 6. to open abscesses; and 7. to decompose and render inert the noxious matter in poisoned wounds.

Of these effects, all but the first two are local. But the production of issues and superficial suppurating surfaces, has for its aim certain favourable influences on the system, or on parts distinct from the one affected, which require notice in this place. The consideration of the local effects will fall most conveniently under the several agents producing them.

Issues. These are running sores, made either by the knife or caustic substances, and afterwards kept open, generally by means of small round bodies called issue peas. in forming them, an incision is made through the skin, into which a pledget of lint is first introduced, and afterwards, when suppuration has been established, the little bodies referred to. The mode in which issues are produced by caustic agents, will be described along with the agents themselves. Setons, which consist of a slender skein of silk or cotton threads, passed by means of a needle through the cellular tissue beneath the skin, and allowed to remain so as to keep up a suppurative discharge, act precisely on the same principles as issues. So also do the superficial suppurating surfaces just alluded to, as one of the effects of escharotics.

Principles on which issues Operate. These various agencies correspond with the epispastics in two of their principles of therapeutic action; those, namely, of revulsion and depletion. The other purposes of that class of medicines, they are in general calulated to fulfil but imperfectly, if at all. As revulsive agents, however, they have considerable power, and, though less energetic than blisters for a short period, have the advantage of a long-continued and steady impression, which renders them sometimes even more effective in very chronic cases. As depleting remedies, they are also, in the long run, more effectual than blisters, unless these are made to imitate issues by being kept steadily suppurating; because the amount of organic matter in pus is vastly greater than in simple serous effusion.

Therapeutic Application of issues. The most important use of issues is in the cure of obstinate chronic inflammation. it is in scrofulous affections of this kind, that they are employed most commonly, and with greatest relative success; and especially in disease of the spinal column, threatening lumbar or psoas abscess. But they may be used also in chronic inflammation of the larger joints, in pectoral inflammations of obstinate character, in chronic meningitis and cerebritis; and, indeed, in all cases of this nature, wherever seated, when the affection is of limited extent, and feeble in its grade of action, but extremely persistent.

Another purpose which issues are calculated to fulfil, is to serve as a point of afflux, or as a drain for morbid tendencies, in certain cases of constitutional disorder, in which there is a disposition to serious or very troublesome local irritation, whether internal or external, as in gouty, rheumatic, scrofulous, and eruptive diseases. They may thus ward off, or alleviate an anticipated and customary attack. .

A third application of issues is to cases in which it is deemed advisable to check some long-continued and habitual discharge, as the hemorrhoidal flux for example, or to heal some old and extensive ulcer to which the system may have become accustomed, or to similar cases in which such discharges have already been arrested, or such ulcers closed. The object of the issue is here obviously the same as in the preceding application of the remedy; namely, to serve as a local point of afflux, or a drain for the morbid tendencies or material, or the accumulated blood, which may result from the cessation of the habitual disease.

The position of the issue must of course be regulated by the seat of the disease, and the special object aimed at. Generally speaking, in cases of chronic inflammation, it should be established as near the seat of the affection as possible. Thus, in disease of the spine, an issue should be made on each side of the column; in obstinate sciatica, behind the large trochanter; in affections of the chest, on parts of the breast or back corresponding with them; and, in meningeal disease, either on the scalp, or at the nape of the neck, as the seat of the disorder may be in the upper part of the brain, or at its base. But when the object is to affect the system generally, and serve as an outlet for morbid tendencies, the issue should be made upon the extremities; either on the arm below the insertion of the deltoid, on the inside of the thigh some inches above the inner condyle, or on the upper and inner part of the leg.