ELASTIN 87 



A fairly strong solution of gelatin, 2 per cent to 4 per cent, gives the 

 xanthoproteic test, but with no previous precipitate by nitric acid; the biuret 

 test, the Millon's test, but with no precipitate. It is precipitated with tannic 

 acid, with alcohol and picric acid. It is not precipitated with acetic acid, 

 hydrochloric acid, mercuric chloride, nor with potassium ferrocyanide, 

 and acetic acid. 



Elastin is found in elastic connective tissue, in the ligamenta 

 subflava, ligamentum nuchae, etc. It is insoluble in all ordinary reagents, 

 but swells up both in cold and hot water. It is slowly soluble in strong 

 caustic soda, when heated. It is precipitated by tannic acid and does not 

 gelatinize. It gives the proteid reactions with strong nitric acid and am- 

 monia, and imperfectly with Millon's reagent. On decomposition it gives 

 4.5 per cent of leucin, a small amount of argenin, and a mere trace of tyrosin. 

 It is prepared by boiling with water, then treating with artificial gastric and 

 pancreatic juices, then boiling again in water, and then extracting with 

 acids, alcohol, and ethers; the remainder is elastin. 



Chondrin is found in the condition of chondrigen in cartilage. 

 It is obtained from chondrigen by boiling. It is soluble in hot water, and 

 in solutions of neutral salts, e.g., sulphate of sodium, in dilute mineral acids, 

 caustic potash, and soda. It is insoluble in cold water, alcohol, and ether. 

 It is precipitated from its solutions by dilute mineral acids (excess redis- 

 solves it), by alum, by lead acetate, by silver nitrate, and by chlorine water. 

 On boiling with strong hydrochloric acid, it yields grape-sugar and certain 

 nitrogenous substances. Prolonged boiling in dilute acids, or in water, 

 destroys its power of forming a jelly on cooling. 



Keratin is obtained from hair, horns, finger-nails, etc. Its com- 

 position is very similar to that of ordinary albumin and is approximately 

 49.5, H 6.5, N 16.8, S 4, O 23.2; the keratins obtained from the various 

 substances are distinct and differ slightly though closely related. Sulphur 

 is the characteristic body found in keratin and occurs as a sulphur-contain- 

 ing radicle. A large amount of mercaptan sulphur can usually be obtained. 

 On decomposition, keratin yields argenin 2.26 per cent, leucin 10 per cent, 

 and tyrosin 4 per cent. 



Keratin is insoluble in water, salt, sodium carbonate, and dilute hydro- 

 chloric acid. It is slowly soluble when warmed in caustic potash or sul- 

 phuric acid. It gives Millon's and the xanthoproteic reactions. 



Neurokeratin is a form of keratin which is found in the white substance 

 of Schwann around the axis-cylinders of nerves. It yields argenin 5 per 

 cent, leucin 10 per cent, and tyrosin 3.5 per cent. 



Products of Proteid Decomposition. The products of proteid de- 

 composition under the influence of oxidizing and hydrolyzing agents are 

 of the greatest significance in indicating the character and composition of 

 the proteid molecule. Cleavage-products of widely varying degrees of com- 



