A nitrogenous substance, or mixture of substances,
   containing sulphur in a loose state of combination, and forming the
   chemical basis of epidermal tissues, such as horn, hair, feathers, and
   the like. It is an insoluble substance, and, unlike elastin, is not
   dissolved even by gastric or pancreatic juice. By decomposition with
   sulphuric acid it yields leucin and tyrosin, as does albumin. Called
   also epidermose.