1. Donders. Accommodation and Refraction of the Eye, p. 319.
2. Fuerst. Graefe's Arch. f. Ophth., v. 65, Ht. 1.
3. Pfalz. Zeit. f. Augenh., v. 25, p. 102.
4. Landrieu. La Clinique Ophtalmologique, v. 20, p. 203.
5. Collins. Ophthalmic Record, v. 24, p. 380.