• (n.) A substance which is formed in mucous epithelial cells, and gives rise to mucin.
(mu´sĭ-jәn) a substance present in mucous cells, convertible into mucin and mucus.
Mu'ci·gen noun [ Muc in + - gen .] (Physiol.) A substance which is formed in mucous epithelial cells, and gives rise to mucin. 
mucigen A substance present in mucous cells that, upon being extruded from the cell, is converted into mucin.