THE NATURE OF FOVE.\L DARK ADAPTATION.* 



By SELIG HECHT.t 



(From the Marine BioloHcal Laboratory, Woods Hole) , .^ 



(Received for publication, August 15, 1921.) '^E^V Ym^K 



»«tamical 



I. QAki>fci* 



In a previous paper (Hecht, 1919-20, c) on the dark adaptation of 

 the human eye, I attempted an analysis of the existing data on periph- 

 eral dark adaptation for the purpose of securing some hint of the 

 physicochemical basis of visual reception. Early in the course of 

 that analysis it became apparent that, aside from the deficiencies in 

 the data themselves, there were lacking some rather elementary 

 concepts on which to rest an objective treatment of the data. For 

 example, there existed no notion of the relation between the intensity 

 of the stimulating light and its photochemical effect in the retina. 

 Moreover, it had apparently never been deemed necessary to entertain 

 any ideas with regard to a mechanism with which to link up the 

 variations in the sensitivity of the retina at different times. 



Clear concepts of at least these two matters lie at the foundation 

 of an}^ attempt toward a rationally objective interpretation of the 

 sensory behavior of the eye. It became necessary, therefore, to 

 supply these defects in terms of what had fortunately been found in 

 the studies of the photosensory responses of certain invertebrates 

 (Hecht, 1921, e). As a result of these assumptions it was possible to 

 analyze the data of dark adaptation of the eye, and to account for 

 the phenomenon in terms of a comparatively simple photochemical 

 mechanism. 



The analysis was made on the best available data. These data 

 were concerned with the periphery of the eye only. This condition 



* Part of the apparatus used in these experiments was secured by means of a 

 grant from the Elizabeth Thompson Science Fund. To the trustees of this Fund 

 I w ish to express my thanks for the grant. 



t National Research Fellow in Chemistry. 



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