1. Hevesy, G., Holst, J. J., and Krogh, A., Biol. Medd., 13, 13 (1937).
2. Sognnaes, R. F., also Leblond, C. P., Belanger, L. F., and Greulich, R. C., also Armstrong, W. D., Ann. N.Y. Acad. Sci., 60, 545 (1955).
3. Pincus, P., Brit. Dent. J., 89, 143 (1950).
4. Pincus, P., Aust. J. Dent., 89 (April 1954).
5. Fisher, R. A., “Statistical Methods for Research Workers”, 21, 1 (Oliver and Boyd, Edinburgh, 1941).