a Cancer Research Campaign Laboratories, Paterson Institute for Cancer Research, Manchester (Great Britain), b Merck, Sharp and Dohme Research Laboratories, West Point, PA (U.S.A.), c Hazleton Microtest, York (Great Britain), a National Institute of Hygienic Sciences, Tokyo (Japan), e Hazleton Laboratories America, Kensington, M D (U.S.A.), I Imperial Chemical Industries, Manchester (Great Brit...
