508 DARK ADAPTATION OF EYE 



The importance of this concept cannot be overemphasized, be- 

 cause it Hes at the foundation of all the work with Mya and Ciona. 

 Together with the logarithmic relation previously explained, it 

 enables one to visualize the initial chemical events necessary for the 

 production of a sensory effect in these animals. 



V. 



If the initial photochemical reaction in retinal sensitivity has 

 something in common with photoreception in Mya, then the applica- 

 tion of the findings with Mya to the data of visual adaptation should 

 yield results of theoretical bearing. The data give the intensities of 

 the light necessary for a visual effect. The photochemical action of 

 this light should therefore be represented by the logarithm of its 

 intensity. These logarithmic values will then give the actual num- 

 ber of units of photosensitive substance decomposed by the Hght, 

 because 



E = k.\ogI. 



We do not know what the value of the constant k is here. But we 

 can always make it equal to 1 by changing the units in which the 

 photochemical effect is measured. Such a change makes no differ- 

 ence in our conclusions, because any unit is a purely arbitrary thing. 



The data treated in this way are given in Figs. 3 to 8. These 

 figures are different experiments taken from the work of Piper (Figs. 

 3 to 7) and of Nagel (Fig. 8). An example of the procedure neces- 

 sary in calculating the data from the published experiments is given 

 in Table I. The first two columns are from the published results. 

 The last two columns are the computed values of the original inten- 

 sities and their logarithms. The data of Table I are given graphically 

 in Fig. 3. 



In the presentation of these experiments I have exercised a certain 

 amount of selection in the following way. Some of Piper's experi- 

 ments are vitiated by the fact that the measurements are made too 

 frequently. For example, in one case nine determinations are re- 

 corded in 11 minutes, some having been made only ^ minute apart. 

 Considering that even a small flash of light retards dark adaptation, 

 it is hard to understand why such an error should have been com- 



