492 ADAPTATIONS TO PHOTIC QUALITY 



with a standard A,500(J, source, they obtained a curve which coincided 

 neither with the rod-spectrum nor with the cone-spectrum as deduced 

 from the ordinary electroretinogram — nor with a curve representing the 

 superposition or resultant of the two. This is rather indigestible, and it 

 is to be hoped that these workers (now estabhshed in Stockholm) may 

 soon decide to turn their recording apparatus upon some animal — 

 Phoxinus for example — which is known to have color vision and whose 

 system is susceptible of cognate studies with various other procedures. 



The only investigator who, without 'hedging', makes an out-and-out 

 claim of color vision for the frog is Birukow. In 1939 he reported experi- 

 ments based upon an application of the optomotor reaction (pp. 301-2) : 

 In 1927, Schlieper had reported that when the alternate stripes on the 

 revolving drum used for eliciting compensatory movements from the 

 animal inside it were respectively colored and gray, there was always 

 some shade of gray to be found which, paired with a given color, would 

 evoke no response from the animal. The animal behaved as though the 

 visual field had become homogeneous, its motion invisible to him — in 

 other words, the animal acted as if it were color-blind, even though it be- 

 longed to a species known positively to have color vision. Schlieper used 

 several diurnal insects, two fishes, and the lizard Lacerta vivipara. By all 

 of these, the optomotor reaction was apparently given only to patterns of 

 brightness differences, and Schlieper concluded that the critical shade of 

 gray which, paired with a color, brought no response, must be a bright- 

 ness match for that color. 



Von Buddenbrock and Friedrich, a few years later, reasoned that if 

 two colors were adjusted in brightness so that each by itself matched the 

 same gray, the two colors would then be equal in brightness for the 

 animal. Such matched colors, applied in alternate stripes to a drum, did 

 effectively stimulate their animals to make compensatory eye movements. 

 Unfortunately, they employed this technique only with invertebrate 

 material — a species of crab. 



Birukow was the first to use their procedure on vertebrates, and he 

 chose to study Rana temporaria. At least, he assumed that Buddenbrock 

 and Friedrich's ideas were correct, and was prepared to try them out on 

 the frog. But he found that neither red nor blue could be 'matched' by a 

 gray for this animal. Apparently the frog differed from the lizard in 

 some way; and the failure to find a gray which, alternated with a color, 

 suppressed the reaction, proved the perception of the color. Birukow 

 could offer no explanation of Schlieper's results with the lizard, nor 



