3O COLOR SENSITIVITY OF THE PERIPHERAL RETINA. 



painted in a gray color of the same brightness as the stimuli, 

 perimetric exploration of the retina gave the following results :* 



His 



It will be seen from this table that Hegg found, in agreement with 

 Bull and with Hess, that the limits of the red and the green zones 

 coincide, as also do those of yellow and blue ; and that the zone of the 

 latter pair is wider than that of the red and green. Similar experiments 

 performed with a smaller area of stimulus gave a lesser extension of the 

 zones of all four colors (/. c., p. 343). 



Kirschmannf found in experiments with non-equated spectral 

 stimuli that blue has the widest zone, and violet the narrowest ; the order 

 of the intermediate zones as found by this investigator is (in descend- 

 ing order), yellow, orange, red, and green. Increase of luminosity of 

 stimulus seems to have no influence upon the width of the zones, and 

 increase of area of stimulus is followed by increased extension of color 

 zone in some cases only. In a second series of experiments, Kirsch- 

 mann employed colored papers representing a great variety of color 

 tones, saturations, and brightnesses. The zones determined by means 

 of these stimuli extend farthest out on the nasal and upper portions of 

 the retina ; their limits do not run parallel with each other, but intersect 

 and re-intersect in a most irregular fashion. It is quite impossible to 

 tell from his determinations what is the relative extension of the differ- 

 ent zones, since their relative widths differ upon different meridians. 

 It would appear, however, that blue has the greatest extension and violet 

 the least. The red and the green stimuli employed by Kirschmann did 



*Ann. d'Ocul., CIX, p. 343. For the sake of uniformity, and in order to 

 facilitate a comparison with the results of other investigators, we have referred 

 Hegg's readings to retinal meridians ; in his paper they are referred to the corre- 

 sponding meridians of the visual field. It will be noticed that Hegg found the 

 yellow-zone to be slightly narrower than the blue-zone. This state of affairs 

 Hegg believes to be due to the greater refrangibility of blue light. 



f A. Kirsehmann. Die Farbenempfindung in indireotem Sehen, Philosophische 

 Studien, VII, 1893, S. 592-614. 



