130 ACIl'ENSER HUSO. 



near the tail ; the ventral and anal fins are also small ; the tail is 

 slightly forked, the upper lobe being elongated by a bony ridge 

 and extending far beyond the lower. The prevailing colour is 

 brown or dark blueish above without spots, and silvery white 

 beneath. 



It is from the sound or air bladder of this and other species of 

 the Sturgeon that the well known substance, called isinglass, is 

 prepared. The Acipenser huso affords the best, but the sounds of 

 all fresh water fish yield more or less fine isinglass, particularly the 

 smaller sorts, found in prodigious quantities in the Caspian Sea, 

 in the Wolga, Danube, Yaik, Don, and even as far north as 

 Siberia. The sounds of the cod-fish, hake, and ling, are frequently 

 employed as a substitute for those of the sturgeon. From the 

 sounds of some of the species of the perch an isinglass is prepared, 

 little inferior to that which is obtained from the air-bag of the 

 sturgeon. An inferior kind is manufactured from the bones, fins, 

 and useless parts of fishes. These materials are boiled in water, 

 the fluid skimmed and filtered, and afterwards concentrated, until 

 it readily gelatinizes on cooling. The method of making isinglass 

 •was long a secret in the hands of the Russians, but it has been 

 discovered, and a full account of it published by Humphrey Jack- 

 son, Esq., in the 63rd vol. of the Philosophical Transactions. 



The production of isinglass requires no artificial heat, neither 

 is the matter dissolved for this purpose, as its fibrous texture 

 would be destroyed by solution, and the mass would become brittle 

 in drying, like glue. It differs from the latter by its fibrous tex- 

 ture, and in being colourless and more transparent. " If," says 

 Mr. Jackson, " what is commercially termed long or short stapled 

 isinglass be steeped a few hours in cold water, the entwisted mem- 

 branes will expand and re-assume their original beautiful hue, and, 

 by a dexterous address, may be made perfectly unfolded. By this 

 simple operation we find that isinglass is nothing more than cer- 

 tain membranous parts of fishes, divested of their native mucosity, 

 rolled and twisted into various forms, and dried in the open air. 

 The sounds or air-bladders of fresh water fish in general are pre- 

 ferred for this purpose, as being the most transparent, flexible, 

 delicate substances. These constitute the finest sorts of isinglass ; 



