1. BARLOW, H. B. (1952). J. Physiol. (Lond.), 116, 290.
2. DITCHBURN, R. W., and GINSBORG, B. L. (1953). Ibid., 119, 1.
3. Text-book of Ophthalmology;DUKE-ELDER, S.,1938
4. LORD, M. P., and WRIGHT, W. D. (1948). Nature (Lond.), 162, 25.
5. LORD, M. P., and WRIGHT, W. D. (1949). Ibid., 163, 803.