SOAP-BARK, the inner bark of Quillaja saponaria, a large tree which grows in Chile. Reduced to powder, it is employed as a substitute for soap, since it forms a lather with water, owing to the presence of a glucoside saponin, sometimes distinguished as Quillai saponin. The same, or a closely similar substance, is found in soapwort (Saponaria officinalis),'m senega root (Polygala senega) and in sarsaparilla; it appears to be chemically related to digitonin, which occurs in digitalis. The saponins (with few exceptions), have the general formula (C n H2n-gOio, and by the action of dilute acids they are hydrolysed into sugars and sapogenins, which are usually inert pharmacologically. An alternative name for them, and especially for those which are pharmacologically active, is sapotoxins; on this nomenclature the hydrolytic products are termed saponins. Applied as a snuff to the mucous membrane of the nose, saponin (either in soapbark or in senega root) promotes a violent sneezing. Solutions injected under the skin are violent local irritants and general depressants.
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)