mucigen

from The Century Dictionary.

• noun A clear substance secreted by the cells of mucous membranes and of certain glands, and which becomes converted into mucin.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Physiol.) A substance which is formed in mucous epithelial cells, and gives rise to mucin.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun physiology A substance formed in mucous epithelial cells that gives rise to mucin.