1. See Earle, W. R., J. Nat. Cancer Inst., 4, 165 (1943). Earle, W. R., Schilling, E. L., and Shelton, E., ibid., 10, 1067 (1950).
2. Abercrombie, M., Hearsman, J. E. M., and Karthauser, H. M., Exp. Cell. Res., 13, 276 (1957).
3. Sachs, L., and Medina, D., Nature, 189, 457 (1961). Vogt, M., and Dulbecco, R., Proc. Nat. Acad. Sci., 46, 365 (1960).
4. Sachs, L., Medina, D., and Berwald, Y., Virology, 17, 491 (1962). Medina, D., and Sachs, L., ibid., 19, 127 (1963).
5. Alfred, L. J., Berwald, Y., Globerson, A., and Prehn, R. T. (unpublished results).