538 ANIMAL SUBSTANCES 



GELATIN 



(Gelatinum) 



Source, &C. Gelatin is an albuminoid substance obtained by boiling 

 skins, cartilages, &c., with water, straining, skimming, and otherwise 

 purifying the solution, evaporating and finally drying by exposure 

 to the air. During the boiling the collagen contained in the carti- 

 lages, &c., is converted into gelatin, which then passes into solution. 



Description. Gelatin occurs in thin sheets, or in shreds or powder, 

 which may be nearly colourless or pale yellow and almost free from 

 odour and taste. In cold water it swells and when heated dissolves ; 

 it is soluble also in acetic acid and glycerin, but not in alcohol, ether, 

 &c. A two per cent, hot aqueous solution should gelatinise on cooling, 

 but this property is destroyed by the prolonged action of heat. 

 Boiling with diluted hydrochloric acid converts it into the hydro- 

 chloride of glutin-peptone. An aqueous solution is precipitated by 

 solution of tannic acid but not by dilute solutions of alum, lead 

 acetate, or ferric chloride. It is rendered insoluble when the aqueous 

 solution is mixed with potassium bichromate and exposed to light ; 

 formic aldehyde produces a similar change. 



Constituents. Gelatin is composed chiefly of the nitrogenous sub- 

 stance glutin. It should not yield more than two per cent, of ash. 



Uses. Apart from its various technical uses, gelatin has been 

 employed as a nutrient and as a styptic, but its value for these 

 purposes has been over-rated. It is also used as a demulcent, and 

 combined with glycerin as a basis for suppositories. 



Isinglass (Ichthyocolla) is the dried prepared swimming bladder of the sturgeon, 

 Acipenser Huso, Linne (N.O. Sturiones), and other species of Acipenser living 

 in the Black Sea and Caspian Sea and the rivers which flow into them. The 

 bladders are cut open, washed, soaked in water, spread out on a board and 

 deprived of the outer, silvery membrane. Dried in sheets they form leaf isin- 

 glass, or several folded together, book isinglass, or rolled and folded, staple 

 isinglass. It is prepared for use by cutting it into thin shreds. 



Isinglass is whitish or pale yellow, semi-transparent, tasteless, but with a 

 more or less perceptible odour. In cold water it softens and swells ; with 

 boiling water it forms a solution which (1 in 50), gelatinises on cooling. It 

 consists chiefly of collagen, about 80 per cent., together with water, about 15 to 

 20 per cent. . 



MUSK 

 (Moschus) 



Source, &C. Musk is the dried secretion from the preputial follicles 

 of the musk deer, Moschus moschiferus, Linne (Phylum Chordata, 

 Class Mammalia, Order Ungulata). 



