. A text-book of physiology : for medical students and physicians . n the same way as it ^ 1 ..-discharges hemoglobin from its Combination Fig 142.—Optogram in eye of rabbit: 1, The nor-in the red COrOUScleS. ma^ appearance of the retina in the rabbits eye: a. The. entrance of the optic nerve; 6, 6, a colorless strip ofThe Solutions thus medullated nerve fibers; c, a strip of deeper color sepa-ls . , . rating the lighter upper from the more heavily pigmentedObtained are alSO lower portion. 2 shows the optogram of a window. bleached upon ex-posure to light. We have in the visual purple, therefo
. A text-book of physiology : for medical students and physicians . n the same way as it ^ 1 ..-discharges hemoglobin from its Combination Fig 142.—Optogram in eye of rabbit: 1, The nor-in the red COrOUScleS. ma^ appearance of the retina in the rabbits eye: a. The. entrance of the optic nerve; 6, 6, a colorless strip ofThe Solutions thus medullated nerve fibers; c, a strip of deeper color sepa-ls . , . rating the lighter upper from the more heavily pigmentedObtained are alSO lower portion. 2 shows the optogram of a window. bleached upon ex-posure to light. We have in the visual purple, therefore, an un-stable substance readily decomposed or altered by the mechanicaleffect of the ether waves, and also, it may be said, by gross me-chanical reactions, such as compression; and there can be littledoubt that the substance plays an important part in the functional * Boll, Archiv f. Physiologie, 1877, 4. t Kiihne, Untersuch. a. d. physiol. Inst. d. Univ. Heidelberg, vol. i,1878. Also The Photochemistry of the Retina, etc., translated by Foster,London, 340 THE SPECIAL SENSES. response of the rod elements. It has been shown that provisionexists in the retina for the constant regeneration of this red will be remembered that the external segments of the rods im-pinge upon the heavily pigmented epithelial cells that lie betweenthe rods and the choroid coat. From experiments upon frogs eyesit appears that a portion of the retina detached from the pigmentcells and bleached by the action of light is not able to regenerate itsvisual purple until again laid back upon the choroid coat. Thisregenerating influence of the black pigmented cells may be con-nected with another interesting relation that they exhibit. Undernormal conditions delicate processes extend from these cells andpenetrate between the rods and cones. When the eye is exposedto light the black pigment migrates along these processes as far evenas the external limiting membrane, and it is possible that t
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