1. Meltzer, M. S., Leonard, E. J., Rapp, H. J., and Borsos, T., J. natn. Cancer Inst., 47, 703 (1971).
2. Baldwin, R. W., and Glaves, D., Clin. exp. Immun., 11, 51 (1972).
3. Kedar, E., Aronov, A., Sulitzenau, D., Israel J. med. Sci., 9, 266 (1973).
4. Law, L. W., and Appella, E. Nature, 243, 83 (1973).
5. Holmes, E. C., Kahan, B. D., and Morton, D. C., Cancer, 25, 373 (1970).