. Kirkes' handbook of physiology . d vision. However, the fact remains that light falling upon the retina bleaches thevisual purple, and this must be considered as one of its effects. It has beenfound that certain pigments, also sensitive to light, are contained in the inner VISUAL PURPLE 659 segments of the cones. These colored bodies are said to be oil globules ofvarious colors—red, green, and yellow—called chromophanes, and are foundonly in the retinae of animals other than mammals. The rhodopsin at anyrate appears to be derived in some way from the retinal pigment, since thecolor is not re
. Kirkes' handbook of physiology . d vision. However, the fact remains that light falling upon the retina bleaches thevisual purple, and this must be considered as one of its effects. It has beenfound that certain pigments, also sensitive to light, are contained in the inner VISUAL PURPLE 659 segments of the cones. These colored bodies are said to be oil globules ofvarious colors—red, green, and yellow—called chromophanes, and are foundonly in the retinae of animals other than mammals. The rhodopsin at anyrate appears to be derived in some way from the retinal pigment, since thecolor is not renewed after bleaching if the retina be detached from its pig-ment layer. The second change produced by the action of light upon theretina is the movement of the pigment cells. On the stimulation by lightthe granules of pigment in the cells which overlie the outer part of the rodand cone layer of the retina become diffused into the parts of the cells be-tween the rods and cones, the melanin granules, as they are called, passing. Fig. 472.—Sections of Frogs Retina Showing the Action of Light upon the Pigment Cells andupon the Rods and Cones (von Gendesen-Stort.) A, From a frog which had been kept in thedark for some hours before death; B, from a frog which had been exposed to light just before beingkilled. Three pigment cells are shown in each section. In A the pigment is collected toward thenucleated part of the cell, in B it extends nearly to the basis of the rods. In A the rods, outersegments, were colored red (the detached one green); in B they had become bleached. In A thecones, which in the frog are much smaller than the rods, are mostly elongated; in B they are all con-tracted. down into tne processes of the pigment cells. A movement 0} the cones andpossibly of the rods is also said to occur, as has been already incidentallymentioned. Under the influence of the stimulus of light the outer parts ofthe cones, which in an eye protected from light extend to the pigment l
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