136 



THE NATimE OF FOVEAL DARK ADAPTATION 



It is worth drawing attention to the fidelity with which the 

 calculated curve of Fig. 6 adheres to the observed facts of dark 

 adaptation. For further testimony Table III is presented showing 

 this agreement in the usual manner. Considering all the things which 

 enter into the experiments and into the calculations, the agreement 

 seems striking. 



This agreement, however, need not be considered an infallible 

 experimentum cruets. It is possible that some other formula might fit 

 the facts just as well. However, the significance which attaches to the 

 agreement is that it follows from a reasoned construction of what may 



TABLE III. 



Comparison of the Observed Values for the Threshold during Dark Adaptation with 

 Those Calculated in Terms of a Bimolecular Reaction. 



take place in the cone cell of the fovea. The circumstance that a 

 similar type of photochemical mechanism differing in local detail of 

 application serves to account for the photosensitive behavior of Mya, 

 and for that of the peripheral retina, heightens the plausibility of the 

 general picture. 



With regard to these local differences in the treatment of the general 

 idea there are several interesting points to be considered. I shall 

 indicate just one of these. For the periphery (rods) of the eye the 

 application of the principle of a reversible reaction depends on the 

 assumption of a logarithmic relation between intensity and photo- 



