1. Medawar, P. B., Colloques Internationaux du Centre National de la Recherche Scientifique, 116, 473 (1963).
2. Mitchison, N. A., Proc. Roy. Soc., B, 161, 275 (1964).
3. Nossal, G. J. V., Ann. NY Acad. Sci., 129, 822 (1966).
4. Goodman, J. W., and Nitecki, D. E., Biochemistry, 5, 657 (1966).
5. Goodman, J. W., and Nitecki, D. E., Immunology, 13, 577 (1967).