The visual pigments of rods and cones in the rhesus monkey, Macaca mulatta.

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Abstract
New microspectrophotometric measurements were made of the photopigments of individual rods and cones from the retina of the rhesus monkey (M. mulatta). The measuring beam was passed transversely through isolated outer segments. The transverse absorbance for rods ranged from 0.02-0.04 and that for cones from 0.01-0.03. The mean absorbance spectrum for rods (n = 25) had a peak at 502 .+-. 2.7 nm. A digitonin extract from the same group of eyes gave a .lambda.max [wavelength of maximum absorption] of 499 .+-. 1 nm. Of a sample of 82 cones, 40 were red (P565 nm) and 42 were green (P536 nm). The mean absorbance spectrum for the green cones was very similar to the Dartnall nomogram, but that for the red cones was narrower. No bleachable, blue-sensitive outer segments were recorded, although structures were found that absorbed at short wave-lengths and were neither photosensitive nor dichroic. If the long wave length and middle wave length cone pigments of the rhesus monkey are assumed to be identical to those of man and if additional assumptions are made about the lengths of human outer segments and about prereceptoral absorption, it is possible to derive psychophysical sensitivities that closely resemble the .pi.5 and .pi.4 mechanisms of W.S. Stiles.