392 DERIVATIVES OF THE PROTEIN-COMPOUNDS. 



ANIMAL, GELATIN. 



Under the term gelatin we comprehend those animal sub- 

 stances which do not exist ready formed in that state in the 

 animal organism, but are produced from certain animal parts by 

 mere boiling with water, so that the still undescribed substance 

 from which this body is so easily obtained, may be regarded as 

 the organic substratum of most of the animal fluids. All these 

 very similar bodies, to which we give the common name of gelatin, 

 are especially distinguished by the following properties; they swell 

 and become very translucent in cold water; they dissolve in hot 

 water; on cooling they separate as translucent, lubricous masses, and 

 are precipitated from the most dilute solutions by chlorine, tannic 

 acid, and most of the salts of the earths and metals. 



There are two principal varities of gelatin to be considered, 

 namely, bone-gelatin, carpenter's glue, or glutin, and cartilage- 

 gelatin or chondrin, although here, as in the case of protein, there 

 appear to be several modifications of each variety. 



GLUTIN. 

 Chemical Relations. 



Properties. In a state of purity, glutin appears in colourless, 

 transparent pieces, which are hard, horny, brittle, heavier than 

 water, devoid of taste and smell, and exhibit no reaction on vege- 

 table colours ; on trituration it does not adhere to the pestle like 

 the protein-compounds. 



Glutin immersed in cold water, becomes soft, swells, and loses 

 its transparency ; in warm water it dissolves, forming a colourless, 

 viscid solution, from which, on cooling, it separates as a jelly ; 

 Bostock^s experiments show that good hard glutin will separate in 

 this manner when diluted with 100 times its bulk of water. After 

 being repeatedly dissolved in hot water, it loses the property of 

 gelatinising. Gelatinised glutin gradually becomes acid on exposure 

 to the air, and then loses its property of fixing and binding. It is 

 perfectly insoluble in alcohol, ether, fats, and volatile oils ; on the 

 addition of alcohol to its warm solution, it coagulates into a white, 

 tenacious, almost fibrous mass, which, however, readily dissolves 

 again when warmed in pure water. 



Acids and alkalies throw down no precipitate from aqueous 



