This section is from the book "Dental Medicine. A Manual Of Dental Materia Medica And Therapeutics", by Ferdinand J. S. Gorgas. Also available from Amazon: Dental Medicine.
Demulcents, also called Lenitives, are medicinal substances which soften and relax the tissues. When applied to irritated or inflamed surfaces these agents diminish the heat, tension and pain. They consist principally of gum or mucilage, often combined with saccharine or farinaceous substances, and, diluted with water, form viscid solutions. By modifying the acridity of the secretions, they are capable, to some degree at least, of relieving irritation in remote organs, although their constitutional effects are chiefly nutritive. Demulcents are employed internally to protect the gastro-enteric surface from irritating substances, especially poisons of an acrid nature; also to relieve irritation and inflammation of the alimentary canal in such affections as diarrhoea, dysentery, enteritis, gastritis, etc.; also in catarrhal affections, for their soothing and lubricating effects from direct contact, and also by reflex action; and they also exert some influence in modifying the acridity of expectorated matters; also in such affections of the urinary passages as cystitis, ardor urinae, as they tend to diminish the acridity of the secretion: also as drinks, to promote the action of the secreting and exhaling organs, and to allay the thirst in fevers: also as light diet, and to suspend substances insoluble in water.
Demulcents are employed externally in the form known as Emollients, to relieve the heat, swelling and pain of inflammation, wounds and burns; to hasten suppuration, as detergents, to cleanse foul ulcers, and to promote suppuration from granulating surfaces. Mixed with water in the form of soft masses, they are commonly termed cataplasms or poultices, and have the effect of softening the parts to which they are applied as vehicles of heat and moisture. Included in the class of demulcents are such substances as gum arabic, flax seed, tragacanth, slippery-elm bark, sassafras pith, marshmallow, benne, quince seed, liquorice root, Iceland moss, Irish moss, starch, arrow root, tapioca, sago, barley, glycerin, pyroxylon, collodion, solution of gutta percha, honey, animal fats, such as lard, in the form of cerate (lard 2 parts, and white wax 1 part), and suet, both containing stearine.