A RETINAL MECHANISM OF EFFICIENT VISION 347 



In a few experiments Garten and Weiss ('07) found that light 

 in which colors could not be recognized, acting for five or more 

 hours, caused the cones of the frog to assume a position inter- 

 mediate between that characteristic of bright light and of total 

 darkness. A limited pigment migration was reported as well. 



These same workers made observations on the fish Abramis 

 brama, contained in a dish lighted by reflection from the cover. 

 Two grades of illumination were chosen : in one colors held within 

 the container could not be distinguished; in the other they were 

 recognizable. According to the results given, in the first grade 

 the cones were maximally retracted in nine retinas and partially 

 so in seven. In the second grade the cones were found shortened 

 in all the eight retinas used, whereas the pigment exhibited no 

 noteworthy change except in the sector constituting the ventral 

 one- third of the eye. 



The foregoing statements reveal the following conditions: 

 Angelucci's several pronouncements in the same publication, if 

 not actually contradictory, at least serve to befog the issue. 

 The use of colored lights by Pergens was unfortunate; moreover, 

 the reliability of certain of his conclusions is questionable. Exner 

 and Januschke's experiments were so ill devised as to furnish no 

 crucial evidence. The results of Garten and Weiss suggest an 

 extreme sensitivity of the cones to low light intensities, whereas 

 the pigment patently has a higher threshold. Finally, there 

 exist no data concerning the responses of the rods to weak light. 



It is clear that if the visual elements and retinal pigment are 

 as highly sensitive to mere traces of light, as often has been 

 held, they can assume no useful positions in the ordinary dim 

 light of rod vision, while the utility of a response evoked under 

 conditions of virtual darkness will still await an explanation. 

 Accordingly, it was with the intent of learning the true conditions 

 that this investigation was undertaken. 



