GEL′ATIN

Syn. Gelatine ; Gélatine , Fr.; Gelatin a , L. Animal jelly, obtained by the prolonged action of boiling water on the organic ti ue of the bones, tendons, and ligaments, the cellular ti ue, the skin, and the serous membranes. Glue and size are coarse varieties of gelatin, prepared from hoofs, hides, skins, .; and isingla is a purer kind, obtained from the air bladders of some other membranes of fish. Prop., . Gelatin is insoluble in cold water, but di olves with greater or le readine on the application of heat, according to the source where it is obtained, and in this state forms a tremulous and transparent jelly on cooling; it is insoluble in both alcohol and ether, and is decomposed by the strong alkalies and acids; with tannic acid it forms an insoluble compound of a buff colour, which is the basis of leather; when acted on by cold concentrated sulphuric acid, it yields glycocoll or gelatin sugar; and when boiled with strong alkalies, it yields glycocoll and leucine. Chlorine pa ed into a solution of gelatin occasions a dense white precipitate (chlorite of gelatin), which ultimately forms a tough, elastic, pearly ma , somewhat resembling fibrin. Tests. Its aqueous solution is recognised as follows:—1. It gelatinises on cooling. 2. It is precipitated by alcohol. 3. Bichloride of mercury gives a whitish flocculent precipitate. 4. Tannic acid or infusion of galls gives a copious yellowish-white, curdy precipitate, which, on being stirred, coheres into an elastic ma , insoluble in water, and incapable of putrefaction, and which, when dried, a umes the appearance of over-tanned leather. 5. The gelatinising property is destroyed by nitric acid. 6. It is not affected by either alum or acetate of lead. In this respect it differs from chondrin. Qual. The goodne of commercial gelatin intended for food is readily proved by pouring boiling water over it, and digesting the two together for a short time. If it is pure and wholesome, its colour remains unaltered, and during its solution it continues entirely free from smell. The resulting solution and jelly are also odourle , neutral to test-paper, free from unpleasant taste, and perfectly transparent. If it forms a yellow gluey-looking ma , and evolves an offensive odour, it should be rejected as of inferior quality, and unfit for culinary purposes. Uses, . Gelatin is largely employed as an article of food, as in soups, jellies, .; but its value in this respect has been, perhaps, overrated. [329] Animals fed exclusively on gelatin die of starvation. But when mixed with other food, especially with substances abounding in albumen, casein, or fibrin, gelatin may be useful as an aliment, and serve directly to nourish the gelatinous ti ues. (Liebig.) Hence gelatin is a fitting substance to form part (but only a part) of the diet of convalescents, as it conveys nutrition directly to these ti ues, without tasking the diminished powers of life for its conversion; but its use should be accompanied by a proper quantity of azotised animal food to supply the elements to the blood, for the support and increase of the muscular ti ue, or fleshy portion of the body. In France gelatin obtained from bones is employed as a part of the diet in hospitals with the best effect, materially abridging the period of convalescence; but when given alone, all animals soon become disgusted with it, and die if not supplied with other food. (D’Arcet.) See Glue , Isingla , and below . [329] The reader interested in this subject should consult a paper by Carl Voit in the ‘Zeitschrift für Biologie,’ viii, 297-388.