1. Dulbecco, R., Proc. U.S. Nat. Acad. Sci., 38, 747 (1952).
2. Lumb, M., Macey, P. E., Spyvee, J., Whitmarsh, J. M., and Wright, R. D., Nature, preceding article.
3. Anderton, K., and Rickards, R. W., see following article.
4. Berger, J., Jampolsky, L. M., and Goldberg, M. W., Arch. Biochem., 22, 476 (1949).
5. Mainland, D., and Murray, I. M., Science, 116, 591 (1952).