18 ANESTHETICS AND MEDICAL GASES-NAMELY, CYCLOPROPANE, ETHYLENE, ETHYL CHLORIDE, ETHYL VINYL ETHER, TRIFLUOROETHYL VINYL ETHER, TRICHLOROETHYLENE, NITROUS OXIDE, OXYGEN, CARBON DIOXIDE, OXYGEN-CARBON DIOXIDE MIXTURES, HELIUM, HELIUM-OXYGEN MIXTURES; HEXAFLUORODIETHYL ETHER A CONVULSIVE AGENT FOR CONVULSIVE SHOCK THERAPY