A text-book of physiology, for medical students and physicians . thanupon the temporal side of the retina. In the red-green blind theperipheral fields of color vision, judged by the individuals ownstandards, may be markedly constricted as compared with the nor-mal retina (see Fig. 150). Functions of the Rods and Cones.—Many facts unite in mak-ing it probable that the rods and cones are different in function. * Baird, The Color Sensitivity of the Peripheral Retina, Carnegie Pub-lication, No. 29, 1905. 350 THE SPECIAL SENSES. They differ in structure ami especially in their connections. As issho
A text-book of physiology, for medical students and physicians . thanupon the temporal side of the retina. In the red-green blind theperipheral fields of color vision, judged by the individuals ownstandards, may be markedly constricted as compared with the nor-mal retina (see Fig. 150). Functions of the Rods and Cones.—Many facts unite in mak-ing it probable that the rods and cones are different in function. * Baird, The Color Sensitivity of the Peripheral Retina, Carnegie Pub-lication, No. 29, 1905. 350 THE SPECIAL SENSES. They differ in structure ami especially in their connections. As isshown in the diagram given in Fig. 151, the cones terminate in theexternal nuclear layer in arborizations which connect with thebipolar ganglion cells, and in the fovea at least this connection is suchthat each cone connects with a single nerve cell and eventually per-haps with a single optic nerve fiber. The rods, on the contrary,end in a single knob-like swelling, and a number of them make con-nections with the same nerve cell. Histologically, therefore, the. 06i 081 oLX 09V Fig. 150.—Perimeter chart showing the highly restricted color fields in the left eyoof a typical ca e •?! o-called red-green color blindness. The ability to distinguish red andgreen, by whatever characteristics of intensity or color they possessed extended for a verysnort distance outside the fovea. It is interesting that the ability to distinguish blue wasin this case limited as compared with a normal eye. conduction paths lor the cones seem to be more direct than inthe case of the rods. These latter elements, moreover, possessthe visual purple, which is lacking in the cones. Lastly, in the eye of i lie totally color blind, in the dark-adapted eye in dim lights, in thecolor-blind peripheral area of the normal eye, and in the eyes of mot distinctly night-seeing animals, such as the mole and the owl, vision eemi to be effected solely by the rods. These facts findtheir Bimplesl explanation perhaps in the
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