1. Demerec, M., Science, 105, 634 (1947).
2. Fahmy, O. G., and Fahmy, M. J., Cancer Res., 30, 195 (1970).
3. Tatum, E. L., Ann. NY Acad. Sci., 49, 87 (1947).
4. Nagai, S., Mutation Res., 7, 333 (1969).
5. Maher, V. M., Miller, E. C., Miller, J. A., and Szybalski, W., Mol. Pharmacol., 4, 411 (1968).