614. ICHTHYOCOLLA.—ISINGLASS. The swimming-bladder or sound of the Sturgeon, a fish found in the Black and Caspian Seas and their tributary streams. The swimming-bladders of other fish are also employed for this purpose, but the isinglass from the Russian species, Acipenser huso, A. guldenstadtii, A. ruthenus, and A. stellatus, is considered the finest and purest. The inner layer of the swimming-bladder is separated from the outer, and after being washed is thoroughly dried. The sheets of commercial isinglass are prepared in various forms—leaf isinglass (single sheets), book isinglass (several sheets folded together), and staple isinglass. In appearance it resembles horn, is of a yellowish-white color, semi-transparent and iridescent. The substance is tough, tearing with difficulty even in the direction of the fibers, but dissolves completely in hot water, forming a transparent jelly on cooling in a solution of 24 parts of the same. Constituents: Gelatin (98 per cent., in the best Russian variety) and from 2 to 30 per cent. of insoluble membrane, the ash amounting to only about 0.5 per cent. Nutritive, easily digested. Emollient and protective externally.