1. Beck, D. J. K. (1947). Bristol Med-Chir. J., 64, 11.
2. Behr, C. (1935). V. Graefes Arch. Ophthal., 134, 227.
3. Henderson, W. R. (1939). Brit. J. Surg., 26, 811.
4. Hughes, E. B. C. (1943). Trans. Ophthal. Soc. U.K., 63, 143.
5. Hughes, E. B. C. (1945). Ibid., 65, 35.