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2. Fulton, J. F., A Text-book of Physiology (W. B. Saunders, Philadelphia and London, 1949).
3. Michaelson, I. C., and Campbell, A. C. P., Trans. Ophthal. Soc. U.K., 60, 71 (1940).
4. Salus, R., Acta Ophthal., 17, 279 (1939).
5. Adler, F. H., Physiology of the Eye (C. V. Mosby, St. Louis, 1965).