File:The principles of light and color- including among other things the harmonic laws of the universe, the etherio-atomic philosophy of force, chromo chemistry, chromo therapeutics, and the general (14780660311).jpg

Identifier: gri_c00033125011227010 (find matches)
Title: The principles of light and color: including among other things the harmonic laws of the universe, the etherio-atomic philosophy of force, chromo chemistry, chromo therapeutics, and the general philosophy of the fine forces, together with numerous discoveries and practical applications ..
Year: 1878 (1870s)
Authors: Babbitt, Edwin D. (Edwin Dwight), 1828-1905
Subjects: Phototherapy Color Color
Publisher: New York, Babbitt & Co.
Contributing Library: Getty Research Institute
Digitizing Sponsor: Getty Research Institute

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the fovea centralis, where the retina is reduced tothose elements alone which arc absolutely necessarv for exactvision. Fig. 201, from Henle, shows a thin transverse section 54Q VISION. of this central depression made on a retina which had been har-dened in alcohol, i. (Lamina hyalina, membrana limitans) is anelastic membrane which divides the retina from the vitreous.The bulbs (seen at 7) are here smaller than elsewhere, measur-ing only the 400th part of a millimeter in diameter, and form aclose and regular mosaic. The other more or less opaqueelements of the retina, are seen to be wanting, except the cor-puscles (6) which belong to the cones. At 5 are seen the fibreswhich unite these with the rest of the retina. This consists ofa layer of fibres of the optic nerve (//) in front, and two layers ofnerve-cells (2 and 4), known as the internal and external ganglionlayers, with a stratum of fine granules (3) between them. Allthese parts of the retina are absent at the bottom of the fovea
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w§> ill!;, ill r Fit;. 201. The Fovea Centralis, or Pit of the Retina. centralis, and their gradual thinning away at its borders is seenin the diagram. Nor do the blood vessels enter the fovea, butend in a circle of delicate capillaries around it. This fovea orpit of the retina, is of great importance for vision, since it is thespot where the most exact discrimination of distances is made.The cones are here packed most closely together, and receivelight which has not been impeded by other semi-transparentparts of the retina. We may assume that a single nervous fibrilruns from each of these cones through the trunk of the opticnerve to the brain, without touching its neighbors, and thereproduces its special impression, so that the excitation of eachindividual cone will produce a distinct and separate effect uponthe sense. (Popular Lectures on Scientific Subjects, by H. nm^Hi^^^H THE RETINA CONSIDERED IN DETAIL. 541 HelmJioltz, p. 207, including Recent Progress in the Theory ofVision

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