Absorption spectra and function of the coloured oil drops in the pigeon retina

Abstract

Absorption spectra of individual oil drops are presented for both the yellow and red fields of the pigeon retina. The general form of the absorption spectra (Fig. 1) is in agreement with earlier measurements. An oil drop belonging to a single cone shows a single region of rapid variation of optical density as a function of wavelength; this region occurs at a longer wavelength in the red field than for a corresponding type of oil drop in the yellow field. A large yellow drop from a double cone in the yellow field may show a rapid rise in density near 460 nm or near 515 nm or near both. The absorption spectra are considered in relation to wavelength discrimination data; this comparison suggests that in the cone types responsible for colour discrimination at long wavelengths only one visual pigment is present in the cone outer segments.