What is a substance of a resinous nature, obtained from the outer bark of the common European birch (Betula alba), or from the tar prepared therefrom; -- called also birch camphor. Watts called?

betulin — A substance of a resinous nature, obtained from the outer bark of the common European birch (Betula alba), or from the tar prepared therefrom; -- called also birch camphor. Watts. (Webster's 1913.)

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