116 THE PROTEIN SUBSTANCES. 



a little more than 0.5 per cent pure crystalline cystine and on account 

 of .the low cystine content as well as for other Reasons the koilin differs 

 from the keratins. 



Keratin is amorphous or takes the form of the tissues from which 

 it was prepared. It is insoluble in water, alcohol, or ether. On heating 

 with water to 150-200 C. it dissolves. It also dissolves gradually in 

 caustic alkalies, especially on heating. It is not dissolved by artificial 

 gastric juice or by trypsin solutions. Keratin gives the xanthoproteic 

 reaction, as well as the reaction with MILLON'S reagent, although the 

 latter is 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, sometimes 

 in such large quantities that it forms a special tissue. It occurs most 

 abundantly in the cervical ligament (ligamentum nuchse). 



Elastin used to be generally considered as a sulphur-free substance. 

 According to the investigations of CHITTENDEN and HART, it is a question 

 whether or not elastin contains sulphur, as it may have been removed by 

 the action of the alkali in its preparation. H. SCHWARZ has been able 

 by another method, to prepare an elastin containing sulphur, from the 

 aorta, and this sulphur can be removed by the action of alkalies, without 

 changing the properties of the elastin; and ZOJA, HEDIN, BERGH, 

 and RICHARDS and GIES * have found that elastin contains sulphur. The 

 most trustworthy analyses of elastin from the cervical ligament (Nos. 

 1 and 2) and from the aorta (No. 3) have given the following results, 

 which compare well with each other: 



c H N s o 



1. 54.32 6.99 16.75 .... 21.94 (HORBACZEWSKI 2 ) 



2. 54.24 7.27 16.70 21.79 (CHITTENDEN and HART) 



3. 53.95 7.03 16.67 0.38 (H. SCHWARZ) 



ZOJA found 0.276 per cent sulphur and 16.96 per cent nitrogen in 

 elastin. HEDIN and BERGH found different quantities of nitrogen in 

 aorta-elastin, depending upon whether HORBACZEWSKI'S or SCHWARZ'S 

 method w r as used in its preparation. In the first case they found 15.44 

 per cent nitrogen and 0.55 per cent sulphur, and in the other 14.67 per 



1 Chittenden and Hart, Zeitschr. f. Biologie/ 25; Schwarz, Zeitschr. f. physiol. 

 Chem., 18; Zoja, ibid., 23; Bergh, ibid., 25; Hedin, ibid.; Richards and Gies, Amer. 

 Journ. of Physiol., 7. 



2 Zeitschr. f. physiol. Chem., 6. 



