138 THE NATURE OF FOVEAL DARK ADAPTATION 



of the fovea itself follows the course of a bimolecular reaction. This 

 is interpreted to mean that there are two photolytic products in the 

 fovea; that they are disappearing because they are recombining to 

 form anew the photosensitive substance of the fovea; and that the 

 concentration of these products of photolysis in the sense cell must 

 be increased by a definite fraction in order to produce a visual effect. 

 5. It is then suggested that the basis of the initial event in foveal 

 light perception is some mechanism that involves a reversible photo- 

 chemical reaction of which the "dark" reaction is bimolecular. Dark 

 adaptation follows the ''dark" reaction; sensory equiUbrium is 

 represented by the stationary state; and light adaptation by the 

 shifting of the stationary state to a fresh point of equilibrium toward 

 the "dark" side of the reaction. 



Dr. W. E. Forsythe of the Nela Research Laboratories was kind 

 enough to calibrate the illumination emitted by the red cross and by 

 the light-adapting screen. I take pleasure in thanking him for his 

 courtesy and help in this connection. 



I also wish to express my appreciation of the gracious cooperation 

 of my various friends who served as subjects in what must have been a 

 tedious performance. I feel particularly indebted to those who were 

 sufficiently interested and kind to serve as subjects for duplicate and 

 triplicate experiments. 



BIBLIOGRAPHY. 



Cobb, P. W., Dark adaptation with especial reference to the problems of night 



flying, Psydwl. Rev., 1919, xxvi, 428. 

 Dittler, R. and Koike, I., tJber die Adaptationsfahigkeit der Fovea centralis, 



Z. Sinnesphysiol., 1912, xlvi, 166. 

 Hecht, S., (a) The photic sensitivity of Ciona intestinalis, J. Gen. Physiol., 1918- 



19, i, 147; (b) Intensity and the process of photoreception, 1919-20, ii, 337; 



(c) The dark adaptation of the human eye, 499; (d) Photochemistry of 



visual purple, 1920-21, iii, 1; (e) The photochemistry of the sensitivity of 



animals to light. Science, N. S., 1921, liii, 347. 

 Inouye, N. and Oinuma, S., Untersuchung der Dunkeladaptation des einen Auges 



mit Hilfe des helladaptierten andern, Arch. Ophth., 1911, Ixxix, 145. 

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Dunkeladaptation des Auges, Z. Psychol, u. Physiol. Sinnesorg., 1904, 



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