The use of isolated or purified stilbenoid compounds including longistyline A-2-carboxylic acid as hypoglycemic agents or to lower serum glucose levels is described. The transparent indicator material may be fixed on the surface by drying and, when a fluorescent material, may be measured through exposure to ultraviolet radiation. A filler element is disposed in the cable jacket and is located adjacent to at least one of the twisted pairs of insulated conductors. 5 parts by weight of a liquid paraffin. The sheath serves as a protecting member for shielding the probe.