622 



THE EYE IN EVOLUTION 



% 

 80 



60- 



40 



30 



20 



NORMAI 



TOTAL 



^ COLOUR BlInD 



\ 



Yellow 



Green 



5lue 



Fig. 



reaction varies directly with the kiminosity of the coloured light employed, 

 Sachs in this way verified the occurrence of a Purkinje shift in the pupillomotor 

 activity of the human eye, finding a maximal reaction in the yellow in light- 

 adaptation, in the blue-green in dark-adaptation ^ ; in totally colour-blind sub- 

 jects (rod-monochromats) the reaction typical of dark-adaptation is obtained 

 (Fig. 765). This technique was first applied by Abelsdorff (1907) to Birds and 

 later and on a much larger scale to Fishes and a host of other animals by v, Hess 

 (1907-22) and others. In some cases the method probably gives an assessment 



of the spectral range and relative lumin- 

 osity of the wave-lengths which stimulate 

 the retina, but its interpretation in terms 

 of colour vision is quite illegitimate. 

 Abelsdorff, for example, showed that the 

 pvipil of the (diurnal) pigeon, or (arhyth- 

 mic) dog was less responsive to green and 

 blue, and that of the (nocturnal) owl or cat 

 more responsive to the blue than the 

 human pupil, v. Hess, however, went 

 much further and argued that if the 

 maximal pupillary contraction were in the 

 yellow, the eye was photopic in type and 

 colour vision was present, if in the green 

 that it was absent ; if the process of 

 adaptation were accompanied by a de- 

 creased sensitivity for the red end of the 

 spectrum and an increased sensitivity for 

 the blue, colour vision was presumed to 

 exist. That this conclusion is illogical is 

 obvious, since it begs the questions that 

 the luminosity curves of animals are the 

 same as in man, that the presence of a 

 duplex retinal mechanism as indicated by 

 the Purkinje shift may subserve photopic and scotopic vision withovit the necessary 

 presence of colour vision (as occvirs in human cone-monochromats, Weale, 1953), 

 and that the pupillary response is always identical with the retinal — a question 

 which becomes very problematical, for example, in fishes in which the iris muscu- 

 lature reacts autonomously. 



(c) Electro-retinographic responses have been applied to the study of colour 

 vision in animals since the demonstration by Himstedt and Nagel (1902) that 

 the retinal action-cvirrents of the frog showed a Pui'kinje shift, the peaks of 

 maximum sensitivity being the same as in the hviman retina — 560 m[i in the 

 light-adapted and 507 m[x in the dark-adapted eye. In further elaboration of 

 this work, Granit and his co-workers (1935-47) found that there were at least 

 three systems in the frog's retina reacting selectively to light of different wave- 

 lengths. Similarly in Birds, Piper (1905) found that a maximal sensitivity to 

 monochromatic lights in diurnal types (fowl, etc.) was at 600 m[j.. while that of 

 nocturnal birds (owl) was at 535 mpi. A similar Purkinje shift has been recorded 

 in the eyes of Fishes (carp, tench, etc.) and Mammals (cat) with a duplex retina, 

 but not in those such as the tortoise with a ( ?) pure-cone retina, nor in nocturnal 

 types with few cones such as the rat and guinea-pig (Granit, 1947). However 

 that may be, it is clear that althovigh the presence of different visual mechanisms 



' For the pupillomotor Purkinje phenomenon see further — Engelking, 1919-24 ; 

 Nakaytuna, 1921-22 ; Rutgers, 1923 ; Laurens, 1923. 



765. — The Pupillomotor 

 Reaction. 



The relative pupillomotor values of 

 coloured light in the normal (light- 

 adapted) eye and in the totally 

 colour-blind (after Engelking). 



