Agents Acting on the Skin.

Irritants,—are substances, which, when applied to the skin, produce more or less of vascular excitement. When employed to excite a reflex influence on a part remote from their site, they are called Counter-Irritants, and may be subdivided into the following groups, viz.:—

Rubefacients, (ruber, red, fucio, I make) ,—those which cause redness (congestion) of the skin, as Mustard, Camphor, Iodine, Capsicum, Turpentine, Ammonia, Pitch, etc. The stronger agents of this subdivision are capable of destroying the tissue if left in contact with it for too long a time.
Epispastics, Vesicants, or Blisters, produce decided inflammation of the skin, and the outpouring of serum between the epidermis and the derma. Cantharides is the agent most used for this purpose, but Mezereon, Euphorbium, etc., are equally efficient.
Pustulants,—affect isolated parts of the skin, as the orifices of the glands, etc., giving rise to pustules. Such are Croton Oil, Tartar Emetic, Ipecacuanha and Silver Nitrate.

Escharotics or Caustics, (escara , a slough, kaiw , I burn),—are substances which destroy the life of the tissue to which they are applied, either by abstracting its water, as Sulphuric Acid,—or by corrosive oxidation, as Bromine. The chief caustics are Potassa, Lime, Arsenous Acid, Zinc Chloride, Silver Nitrate, Corrosive Sublimate, Mercuric Nitrate, Mineral Acids, Bromine, Zinc and Copper Sulphates. Chromic Acid is one of the most efficient, but must be carefully used, it being a violent poison.

Astringents, (ad, to, stringo, I bind),—produce contraction of muscular fibre, and condensation of other tissues, also lessen secretion from mucus membranes. Remote Astringents, act on internal organs through the circulation, as Gallic Acid, Sulphuric Acid and Lead Acetate. Local Astringents affect the part to which they are applied, as Tannic Acid, Alum, salts of Bismuth, Lead, Copper, Zinc, and Cadmium, the per-salts of Iron, the Mineral Acids; Galls, Kino, Catechu, and other plants containing Tannic Acid.

Styptics and Hemostatics, (stufw , I contract;—aima , blood, stasiV , a standing),—are agents which arrest bleeding; Styptics being applied locally, and Hemostatics administered internally, for the same purpose. Some act mechanically, by promoting clot-formation in the mouths of the bleeding vessels, others by causing the vessels themselves to contract, and thereby check the flow of blood. The principal members of this class are the following named, to wit,—

Styptics,—Acids, Alum, Ferric Chloride, Ferrous Sulphate, Zinc Sulphate, Lead Acetate, Silver Nitrate, Matico, Cold, Spider's Web, Tannic Acid and all the Vegetable Astringents.
Hemostatics,—the dilute Mineral Acids, especially Sulphuric, Gallic Acid, Ergot, Digitalis, Hamamelis, Ipecacuanha, Lead Acetate, and Oil of Turpentine.

Emollients and Demulcents, (emollio, I soften, demulceo, I soothe),—are substances which soothe and protect tissues to which they are applied. Emollients act as external demulcents, being used upon the cutaneous surface, to soften and relax the part, dilate the vessels, diminish tension, and protect from the air or from friction. Demulcents are generally of oleaginous or mucilaginous character, employed on the mucous membranes for similar purposes. The chief agents comprised in these two groups are as follows,—

Emollients. Demulcents.
Petrolatum, (Vaselin). Isinglass. Bland Oils.
Soap Liniment. Starch. Marsh-mallow. Honey.
Adeps, (Lard). Glycerin. Tragacanth. Almond Oil.
Cacao butter, (Ol. Theobromae). Acacia. Cetraria. Starch.
Flaxseed Poultices. Olive Oil. Liquorice. Glycerin. Olive Oil.

Protectives,—are articles employed to cover an inflamed or injured part, and to protect it from the air, water, friction, etc. Collodion and Gutta-percha are those in general use, but Cotton Wool, and certain plasters, the Adhesive, Lead or the Soap Plaster, may also be employed.

A Compend of Materia Medica, Therapeutics, and Prescription Writing, 1902, by Sam'l O. L. Potter, M.D., M.R.C.P.L.