1. Buell, P., Cancer Res., 34, 1189–1191 (1974).
2. Zuckerman, A. J., Br. med. J., 1, 49 (1972).
3. MacMahon, B., Cancer, 10, 1045–1054 (1957).
4. Bodmer, J., and Bodmer, W. F., Israel J. Med. Sci., 9, 1257–1268 (1973).
5. Demographic Year Book, 1956, 256–266 (United Nations, New York, 1956).