1. 1) Atkin, N. B., Richard, B. M., and Ross, A. J.: Brit. J. Cancer, 13, 773 (1959).
2. 2) Klein, E., and Klein, G.: Nature, 166, 166 (1950).
3. 3) Leuchtenberger, C., Leuchtenberger, R., and Davis, A.M.: Am. J. Pathol., 30, 65 (1954).
4. 4) Ojima, Y., Inui, N., and Makino, S.: Gann, 51, 371 (1960).
5. 5) Ojima, Y., Inui, N., and Takayama, S.: Gann, 53, 123 (1962).