Aipocere or grave wax or mortuary wax is the insoluble residue of fatty acids from pre-existing fats contained in decomposing material such as a human cadaver. It is formed by the slow hydrolysis of fats in wet ground and can occur in both embalmed and untreated bodies. It is generally believed to have first been discovered by the Frenchman Fourcroy in the 18th century; however, Sir Thomas Browne describes this substance in his discourse, Hydriotaphia, Urn Burial of 1658: