1. Abercrombie, M., and Heaysman, J. E. M., Expl. Cell Res., 6, 293 (1954).
2. Stoker, M. G. P., and Rubin, H., Nature, 215, 171 (1967).
3. Dulbecco, R., Nature, 227, 802 (1970).
4. Kruse, P. F., and Meidema, E., J. Cell Biol., 27, 273 (1965).
5. Todaro, G., Matsuya, Y., Bloom, S., Robbins, A., and Green, H., in Growth Regulating Substances for Animal Cells in Culture, Wistar Institute Symposium Monograph 7 (edit. by Defendi, V., and Stoker, M.), 87 (Wistar Institute Press, Philadelphia, 1967).