1. Physiological Optics, Vol;Helmholtz
2. Igersheimer.-Arch. f. Ofihthal., Vol. XCVI, p. 1.
3. Marlow.-Jl. Med. Soc., State of New York, Vol. III, No. 9, September, 1923.
4. Evans, J. N.-Amer. Jil. of Ofhthal., Vol. IX, No. 7, July, 1926.
5. An Introduction to the Study of Colour Vision;Parsons, J.H.,1915