36 PHYSIOLOGICAL CHEMISTRY. 



tions with MILLON'S reagent, even though they are not always, 

 typical. 



In the preparation of keratin a finely-divided horny structure 

 is treated first with boiling water, then consecutively with diluted 

 acid, pepsin-hydrochloric acid, and alkaline trypsin solution, and, 

 lastly, with water, alcohol, and ether. 



Elastin occurs in the connective tissue of higher animals, pome- 

 times in so large quantities that it forms a special tissue. It occurs 

 most abundantly in the cervical ligament (ligamentum nuchae). 

 It seems that there is more than one kind of elastin. 



Elastin, according to the general view, is free from sulphur. 

 According to the investigations of CHITTENDEK and HAKT, it is a 

 question whether or not elastin contains sulphur which is removed 

 by the action of the alkali in its preparation. The most trust- 

 worthy analyses of elastin from the cervical ligament have given 

 the following results : 



C H > T O 



54.32 6.99 16.75 21.94 (HORBACZEWSKI.) 



54.24 7.27 16.70 21.79 (CHITTBNDEN and HART.) 



As splitting products we find leucin, tyrosin (in small quantity), 

 glycocoll, amido-valerianic acid, ammonia, and others. No indol 

 or phenol is obtained on putrefaction. On heating with water in 

 closed vessels, on boiling with dilute acids, or by the action of a 

 proteolytic enzym, the elastin dissolves and splits into two chief 

 products, caKed by HOEBACZEWSKI Jiemielastin and elastinpeptone. 

 According to CHITTEKDEN and HAKT, these products correspond 

 to two albumoses designated by them protoelastose and deutero- 

 elastose. The first is soluble in cold water and separates on heating, 

 and its solution is precipitated by mineral acid as well as by acetic 

 acid and potassium ferrocyanide. The watery solution of the other 

 does not become cloudy on heating, and is not precipitated by the 

 above-mentioned reagents. 



Pure dry elastin is a yellowish-white powder; in the moist state 

 it appears like yellowish-white threads or membranes. It is insol- 

 uble in water, alcohol, or ether, and shows a resistance against the 

 action of chemical reagents. It is not dissolved by strong caustic 



