1. Fildes, P., Richardson, G. M., Knight, B. C. J. G., and Gladstone, G. P., Brit. J. Exp. Path., 17, 481 (1936).
2. Roberts, R. B., et al., Carnegie Inst. Wash. Publ., 607 (1955).
3. Morse, M. L., Proc. U.S. Nat. Acad. Sci., 45, 722 (1959).
4. Glanville, E. V., and Demerec, M., Genetics, 45, 1359 (1960).