1. ADAMUK, E. (1866). Zbl. med. Wiss., 4, 561.
2. ADLER, F. H. (1924). Arch. Ophthal., N. Y., 53, 1.
3. ATTREE, V. H. (1950). J. sci. Instrum., 27, 43.
4. BOURQUIN, E. (1925). Rev. gdn. Ophtal., Paris, 39, 491.
5. CoLL,J., DuKE-ELDER, P. M., and DUKE-ELDER, S. (1931). J. Physiol., Lond., 71, 1.