1. For general reviews, see Snell, G. D., in Conceptual Advances in Immunology and Oncology, 16th Ann. Symp. on Fund. Cancer Res., 1962, Univ. of Tex. M. D. Anderson Hosp. and Tumor Inst., Houston, Tex., 323 (Hoeber Medical Division, Harper and How, Publishers, Inc., New York, Evanston, and London, 1963), and Owen, H. D., Amer. J. Hum. Genetics, 34, 366 (1959).
2. Snell, G. D., J. Nat. Cancer Inst., 21, 843 (1958).
3. Snell, G. D., and Stevens, L. C., Immunology, 4, 366 (1961).
4. Hellström, K. E., Nature, 199, 614 (1963).
5. HeUström, K. E., Science, 143, 477 (1964).