1. Delafield and Prudden. Text Book of Pathology, 9th Ed., p. 26.
2. Parsons, J. Herbert. The Pathology of the Eye, vol. II, p. 469.
3. Collins and Mayou. Pathology and Bacteriology of the Eye, p. 256.
4. Hepburn. Trans. Ophthal. Soc. of the United Kingdom, vol. XXXII, p. 361.