1036 PEPSIN, HEMATOSIN, GLOBULIN, &C. 



GELATIN. 



This is the basis of glue, size, and animal jelly, and is 

 obtained by the action of boiling water upon skin, tendons, liga- 

 ments, cellular tissue, and serous membranes. These materials 

 are dissolved almost entirely, by continued digestion in boiling 

 water, and the solution forms a jelly on cooling. A substance 

 is obtained from the permanent cartilages, by a similar treatment, 

 which also gelatinizes, but is not precipitated by tannin, and 

 differs in other respects from gelatin ; the latter substance 

 was first distinguished, as a peculiar principle, by Miiller, and 

 named chondrin. Gelatin is not found in the blood or any of 

 the healthy fluids, nor does it exist as such in the solids, but is 

 a product of their alteration by boiling water, as dextrin and 

 starch-sugar are products of the alteration of starch by the 

 same agent. 



Gelatin is distinguished by its ready solubility in warm water, 

 and property of forming a stiff jelly when it cools. As prepared 

 from different materials, gelatin differs considerably in viscidity* 

 Its viscidity, as prepared from skins, is inversely as their softness 

 and flexibility. The most adhesive of its forms, glue, is prepared 

 from the clippings of hides, hoofs and other refuse of the tan- 

 yard. The solution is boiled, filtered above 120, and after 

 evaporation poured into square boxes to gelatinize. The jelly 

 is cut into slices, and when dried in the air upon a netting takes 

 the form of the cakes of glue. Glue is dissolved for use by a 

 water-bath heat, after being softened by steeping in cold water. 

 Size, which is less tenacious and adhesive, is prepared from 

 parchment, fish skin and several animal membranes ; isinglass 

 from the entrails of several species of fish, particularly the stur- 

 geon. The latter gelatin gives a colourless solution, which has 

 no disagreeable taste or odour; it forms a firm jelly on cooling 

 when dissolved in 100 times its weight of water. 



Gelatin is insoluble in alcohol and ether. When burned it 

 leaves behind a small portion of bone-earth. Its solution in 

 water is not precipitated by alum, by neutral protosulphate of 

 iron, by either the neutral or basic acetate of lead ; all of which 

 precipitate a solution of the chondrin of cartilage. Gelatin is 

 readily soluble in diluted acids and alkalies. Its solution in 



