The Encyclopedia Americana (1920)/Keratin
KERATIN (from Gr. keras, a horn), a substance, obtained from claws, feathers, hair, horn, nails, wool, and other epidermal appendages. This tissue or substance is distinguished from gelatinous tissue by becoming soft when acted on by water for some time but no glue is produced. It is insoluble in alcohol and in ether and contains a high percentage of sulphur.