Cholic acid was a crystalline acidic substance secreted by the humanoid liver. This acid played an important role in digestion. When Chief Engineer Geordi La Forge and Lieutenant Barclay were analyzing a corrosive organic solvent in a Jefferies tube, La Forge mentioned there were high levels of cholic acid enzymes which were dissolving a bulkhead and conduit. Upon completing a biospectral analysis, the solvent was later learned to be that of Lieutenant Worf's venom, as he was spraying it throughout the ship after becoming infected with Barclay's Protomorphosis Syndrome. (TNG: "Genesis" )