Abstract: A medicinal composition which comprises a compound of the formula:CH.sub.3 (CH.sub.2)nCH.dbd.CHCO.sub.2 Hwherein n represents 10, 12, 14 or 16, or a pharmaceutically acceptable salt thereof and a pharmaceutically acceptable carrier; a method for testing diabetes or improving lipid metabolism by the administration of said composition to a human being; and a process for the separation of said compounds from freshwater clam which comprises subjecting freshwater clam to the extraction with hot water and/or an aprotic solvent and then purifying the resultant.