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J. Dowling (personal communication).
The fact that the effect is obtained when the dissected retina is exposed to light in vitro also rules out the necessity of absorption of the energy by the choroid or the pigment epithelium for this reaction to occur. Repetition of this experiment in vitro would eliminate reflectance factors.
R. Granit, in The Eye, edited by H. Davson (Academic Press Inc., New York, 1962), Vol. 2, pp. 657 cf.
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E. Margoliash (these data are found in Refs. 17 and 18).
One may question the validity of plotting the absorption coefficient with the data describing log relative sensitivity (Fig. 6) since the absorption coefficient curves may be varied by changing the thickness of the absorbing layer (d) or by manipulating the concentration (r) of the absorbing material. (The values of d and r used by Margoliash are not given.) However, the author doubts that any such manipulation will provide a reasonable fit to the data presented in this experiment. The ellipsoid layer is only a few microns thick and the concentration of cytochromes cannot be very great.
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J. Dowling, J. Gen. Physiol. 46, 1287 (1963).
In his article Dr. Cone briefly considers the role played by waveguide modal patterns in Dr. Dowling's preparations. One tacit assumption made by Dr. Cone in the treatment of these data is that no changes in modal pattern occur during near-total bleaching. One may inquire as to the effect of extensive bleaching of the rhodopsin upon the indexes of refraction and the configuration of the receptor cell, and the interstitial matrix, etc. Small differences in physical characteristics and absorption become important when one considers the receptor as a waveguide. One may ask also whether the conditions employed by Dr. Dowling in his experiment favored the simultaneous transmission of multiple waveguide modal patterns? These questions are not raised in criticism of Dr. Dowling's experiment, but rather are directed toward generalizations of Dr. Cone's interpretation.
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