478 ADAPTATIONS TO PHOTIC QUALITY 



light, thus further demonstrating, to Bauer's satisfaction, a Purkinje 

 phenomenon. 



Box salpa preferred light coming through blue glass + frosted glass to 

 that transmitted by frosted glass alone. Bauer concluded that this 

 response was to hue as such, since the blue light was certainly the dim- 

 mer of the two and Box salpa is strongly positive to light. If it were 

 responding to brightness rather than to color, the fish would surely have 

 gone to the white light instead of to the blue. 



Hess came forward with an explanation of Bauer's apparent demon- 

 stration of a Purkinje phenomenon in fishes. He argued that in the light- 

 adapted fish the expanded retinal pigment would constitute a yellow 

 filter, reducing the brightness of blue stimuli relative to long-wave ones. 

 He found that a blue light had to be made four times as intense to bal- 

 ance a yellowish-red light for a photopic fish as for a scotopic one, and in 

 experiments with light-adapted tiny carp he had to raise the intensity of 

 a blue light six- or eight-fold to keep the fishes evenly distributed through 

 it and a red which balanced the lower blue for the dark-adapted fish. 



While no more conclusive-looking demonstration of the Purkinje 

 phenomenon has ever been made, Hess concluded that it was not that 

 dark-adaptation increased the brightness of blue and decreased the bright- 

 ness of red — the true Purkinje phenomenon — but rather that light-adap- 

 tation left the brightness of long-wave stimuli unchanged and pulled 

 down the brightness of short-wave ones. Some such effect may indeed 

 occur along with the Purkinje changes, if the retinal fuscin actually does 

 have any peak of absorption at all (which has yet to be demonstrated) , 

 and moreover has it in the short-wave end of the spectrum. But any such 

 phenomenon is rendered very improbable by the recent demonstration 

 that blue and red values are not altered for dark-adapted fishes whose 

 retinal pigment has been artificially expanded with adrenalin (v. i.). 



Hess denied the existence of red-shyness, or at least that it indicated 

 color-vision; but he failed to look for it in specimens which would be 

 most likely to show it — mature, light-adapted fish of negatively photo- 

 tropic species. His finding that red and blue lights could be so balanced 

 that a light-adapted fish would show no preference for either — even sup- 

 posing that others had found the same thing, which they have not — 

 might only mean that the fish had had opportunity to become accustomed 

 to the red and recover from its red-shyness; he does not give the time- 

 periods involved. Where Hess finds that a fish will leave a blue and go 

 to a bright red, he may have been dealing with a red-loving fish — he does 



