ELASTIN. 115 



tity of the sulphur (lead-blackening) it contains, while according to its 

 solubility in gastric juice it must stand close to the proteins. Another 

 substance, nearly like keratin, is the horny layer in the gizzard of 

 birds. According to J. HEDENIUS this substance is insoluble in gastric 

 or pancreatic juice, and acts quite like keratin. According to K. B. 

 HOFMANN and PREGL, 1 who call this substance koilin, it does not yield 

 any cystine on hydrolysis, or at least not a determinable quantity, and 

 differs from the keratins in this and other regards. 



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 nuchae). 



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 

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

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

 ing the properties of the elastin; and recently ZOJA, HEDIN, BERGH, 

 and RICHARDS and GIES 2 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: 



1 Hedenius, Skand. Arch. f. Physiol., 3; Hofmann and Pregl, Zeitschr. f. physiol., 

 Chem., 52. 



2 Chittenden and Hart, Zeitschr. f. Biologic, 25; Schwarz, Zeitschr. f. physiol. 

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

 Journ of Physiol., 7. 



3 Zeitschr. f. physiol. Chem., 6. 



