NITROGENOUS ORGANIC CELL-CONSTITUENTS. 107 



In solution gelatin rotates the plane of polarized light to the left 

 ( — 130° at 25° C). In watery solutions gelatin is precipitated by tannic 

 acid, alcohol, and mercuric chloride ; but not bj r acetic acid, which serves 

 to distinguish it from chondrin ; nor by potassium ferrocyanide and acetic 

 acid, which separates it from other proteids; nor acetate of lead, which 

 precipitates chondrin. When boiled with cupric sulphate and potassium 

 hydrate, the blue solution becomes red without depositing oxide of 

 copper. Gelatin readily undergoes putrefaction, and among the products 

 leucin, ammonia, and some of the fatty acids are found. 



c. Chondrogen. — Chondrogen is found in the intercellular substance 

 of hyaline cartilage, and in the cartilage of bone before ossification. It 

 derives its name from the fact that when boiled with water it forms 

 chondrin, — a point which serves to distinguish it from fibro-cartilage, 

 which, when treated in the same wa}- with boiling water, forms gelatin, and 

 not chondrin. Chondrogen is insoluble in cold water, but if dried before- 

 hand, when immersed in cold water will swell up slightly. It swells very 

 slightly in acetic acid, and may be dissolved by the concentrated mineral 

 acids and caustic alkalies. When subjected to prolonged boiling with 

 water it dissolves and forms an opaline solution, which forms a jelly 

 when cooled. 



d. Chondrin. — As just stated, chondrin is the result of prolonged 

 boiling of chondrogen in water. When solutions of chondrin in water 

 cool they form a stiff jelly, which is insoluble in cold water, but soluble 

 in alkalies and ammonia. When solutions of chondrin are evaporated, 

 a hard, translucent, yellowish, gummy mass results, which is insoluble 

 in alcohol and ether, swells slightly in cold and dissolves tolerably 

 readily in hot water and solutions of the alkalies. Prolonged boiling of 

 watery solutions of chondrin destroys its power of gelatinizing, though 

 the other properties of chondrin are not thereby altered. It is precipi- 

 tated from its solutions by alcohol. It differs from gelatin in that it is 

 precipitated by the mineral acids even when they are dilute ; an excess 

 of the reagent dissolves the precipitate. It is also precipitated by 

 solutions of sulphurous acid. It is precipitated by acetic acid, the 

 precipitate not being soluble in excess unless some alkaline salt be 

 present. It is precipitated in abundant flocculi by solutions of alum, 

 which readily dissolve in an excess, and the fluid becomes clear and 

 transparent. It is precipitated with acetate and subacetate of lead, 

 nitrate of silver, and cupric sulphate. Tannic acid and chlorine water 

 precipitate it, as in the case of gelatin. It rotates the plane of polarized 

 light to the left. Chondrin also is readily decomposable, and when 

 subjected to prolonged heat with concentrated hydrochloric acid is 

 decomposed, with the formation of nitrogenous compounds which have 

 the power of reducing the cupro-potassium test ; a body resembling acid 



