The red‐sensitive pigment in normal cones

It is ten years since it was demonstrated by retinal densitometry that there were two visual pigments in the red-green range upon the normal fovea, and only one upon the protanope's (Rushton, 1955). Now that this pigment chlorolabe has been studied by itself in the protanope (Rushton, 1963a, b, c) and a more red-sensitive pigment erythrolabe has been studied by itself in the deuteranope (Rushton, 1965a, b) we are in a position to begin the study of the mixture on the normal fovea. The red pigment is the easiest to isolate, so in this paper we shall analyse that and show that it appears to be identical with erythrolabe of the deuteranope by the four kinds of measurements that can be used-the difference spectrum, the action spectrum, the photosensivity and the regeneration rate. It will also be shown to be a visual pigment by the two kinds of measurement that can be used-the correspondence of the action spectrum with the visual spectral response of Stiles' red mechanism 7T5 and the correspondence of the time course of pigment regeneration with the dark adaptation curve of T5.