File:A text-book of physiology, for medical students and physicians (1907) (14778085935).jpg

Identifier: textbookofphysio1907howe (find matches)
Title: A text-book of physiology, for medical students and physicians
Year: 1907 (1900s)
Authors: Howell, William H. (William Henry), 1860-1945
Subjects: Physiology Physiology
Publisher: Philadelphia, London, W.B. Saunders Co.
Contributing Library: Columbia University Libraries
Digitizing Sponsor: Open Knowledge Commons

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on and sets up nerveimpulses that arouse in the brain the sensation of white. On theother hand, when not acted upon by light this same substance under-goes assdmilatory processes that in turn set up nerve impulses whichin the brain give us a sensation of black. There are in the retina alsoa red-green and a yellow-blue substance. The former when actedupon by the longer rays undergoes disassimilation and gives asensation of red, while the shorter waves cause assimilation andproduce a sensation of green. A similar assumption is made forthe yellow-blue substance. The essence of the theory may be stated,therefore, in tabular form, as follows *: Photochemical Substance.Red-green Retinal Process.Disassimilation = 1 Assimilation Tr „ , , f Disassimilation Yellow-blue \ Assimilation White-black. f Disassimilation\ Assimilation Sensation.redgreenyellowbluewhiteblack It will be observed that the theory gives an independent ob-jective cause for the sensations of white, black, and yellow, and in
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i L63. Schema to illu trate the Hcrinc theory of color vision.—(Foster.) Thecurves indicate the relative inten itie i timulation ol the three color i ubstanoes by dif«ferenl part I the pectrum. Ordinates above the axis, X—X, indicate oatabolic chancesimilation), those below anabolic changes (assimilation). Curve a represents theconditioni for ih<- black-white substance. Ii is stimulated by all the rays l the visiblespectrum with maximum inten ity in the yellow. Curve c representi the red-green sub-stance, the longer wave lengths causing disassimilation (red), the horter ones assimilation(greei mditions for the yellow-blue substance. this respect satisfies the objections made on this score to the Young-Helmholtz theory. It fits better, also, the facts of partial and totalcolor blindness. In the latter condition one may assume, in terms of* For discussion of color theories see Calkins, Archiv f. Physiologic,L902, uppl. volume, p, 21 1. PROPERTIES OF THE RETINA. 355 KALEV

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