1. Gardner, W. U., Kirschbaum, A., and Strong, L. C., Arch. Path., 29, 1 (1940).
2. Levan, A., and Hauschka, T. S., J. Nat. Cancer Inst., 14, 1 (1953).
3. Billingham, R. E., Brent, L., and Medawar, P. B., Nature, 172, 603 (1953).
4. Koprowska, I., and Koprowski, H., Cancer Res., 13, 651 (1953).
5. Koprowska, I., and Koprowski, H., J. Nat. Cancer Inst., 14, 627 (1953).