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2. ADRIAN, E. D., and MATTHEWS, R. (1928). Ibid., 65, 273.
3. FERREE, C. E., and RAND, G. (1936). Arch. Ophthal., Chicago, 15,1072. REm, D. D. (1949). Brit. J. soc. Med., 3, 101.
4. ROBERTSON, C. J. (1935). Arch. Ophthal., Chicago, 14, 82.
5. ROBERTSON, C. J. (1936). Ibid., 15, 423.