MUCILAGE, a term which denotes a viscid or glutinous mixture of water and any gummy vegetable substance. The principal sources of mucilaginous matters are enumerated under Gum (vol. xi. p. 276). A mucilage indicates a physical condition or property rather than any definite chemical constitution, and consequently it may possess various characters, but as a rule the term is restricted to the bodies which swell into a kind of jelly with water, having the insoluble gum bassorin as their principal constituent. Such mucilages are useful in medicine as emollients and demulcents, and in the arts as thickeners (in calico-printing, dyeing, &c.). A remarkable variety of mucilage has been recently obtained by Stanford of Glasgow from certain of the commoner kinds of Algae, and called from its source algin. The Laminariae, yield it in abundance and in a comparatively colourless condition; it is also found in Fuci, but darkly coloured. It is a substance of considerable thickening character, and has the peculiar property of gelatizing on the addition of a dilute mineral acid. A solution containing only 2 per cent, of algin when thus treated sets into a solid jelly. Alcohol has the same effect upon it. It is extracted from the plants by sodium carbonate, and as it can be obtained in large quantity it may become useful in the dressing of fabrics, or as a thickener in calico-printing.