ELASTIN. KERATIN. 61 



ELASTIC. 



Elastin occurs in the connective tissues, in the cervical liga- 

 ment (ligamentum nuchae) very abundantly. It differs from most 

 of the proteins in containing no sulphur, except possibly some 

 that is loosely combined with the molecule. In the moist state it 

 is very elastic; when dry it is hard and brittle. By the action 

 of the digestive ferments it is decomposed into bodies called elas- 

 toses, similar to the albumoses. It gives the general reactions of 

 the proteins. 



145. Prepare elastin from the cervical ligament of an ox by 

 cutting it into thin slices and boiling it for several days to remove 

 the gelatin. Boil then with 1-per-cent. potassium hydrate for 

 several hours, afterward with water. Repeat the boiling with 10- 

 per-cent. acetic acid; then let it stand twenty-four hours in 5- 

 per-cent. hydrochloric acid. Wash with water, boil with 95-per- 

 cent, alcohol, and extract with ether to remove the fat. For the 

 complete removal of the latter more than a week may be required. 



146. Try the tests used for sulphur in albuminous sub- 

 stances, and see that it is not present. 



KERATIN. 



The keratins are the chief constituent of the horny part of 

 the epidermis, of hair, horns, nails, feathers, etc. They contain 

 a large amount of sulphur, 4 or 5 per cent., a part of which 

 is so loosely united that it is set free by boiling water. It is 

 owing to this sulphur that the salts of lead, silver, and some other 

 metals act as hair-dyes, the sulphur uniting with the metal to 

 form a dark-colored sulphid. The keratin is not at all attacked 

 by the gastric or pancreatic juices. It is decomposed when heated, 

 giving the odor of burnt horn. It is insoluble in water, and gives 

 the xanthoproteic and Millon's reactions. 



147. Prepare keratin by boiling some horn-shavings with 

 water and then digesting them in succession in a dilute solution of 

 pepsin containing 0.2-per-cent. HC1, and a trypsin solution. Wash 

 with water, alcohol, and ether. 



