The Collaborative International Dictionary of English v.0.48:

Betulin \Bet"u*lin\, n. [L. betula birch tree.] (Chem.)
   a term originally applied to a substance obtained as a resin
   or tar by extraction from the outer bark of the common
   European white birch (Betula alba); now referring to the
   chemical compound (C30H50O2) having a
   cyclopentanophenanthrene ring system, which is the main
   constituent of that extract, and which may be obtained
   crystalline; -- called also birch camphor. --Watts.
   [1913 Webster +PJC]