COLOR SENSITIVITY OF THE PERIPHERAL RETINA. I/ 



is inappropriate and can not properly be applied even to the extreme 

 periphery. There is no evidence of a difference in structure between 

 the various parts of the normal retina. The keener sensitivity of the 

 fovea and paracentral region can be explained in terms of greater lumi- 

 nosity of retinal image. This, of course, is a definite rejection of the 

 explanation offered by Helmholtz. An important feature of Landolt's 

 papers is his insistence that no investigation of color vision is complete 

 unless it takes into account the condition of retinal adaptation and deter- 

 mines the relative luminosity of the stimuli employed. 



Briesewitz* employed circular discs of colored paper, which he 

 moved in from the periphery upon a black background. His explora- 

 tion of four normal retinas yielded the following results : There is a 

 gradual decrease of color sensitivity with increasing distance from the 

 fovea ; this decrease is most rapid on the temporal retina ; yellowish-red 

 and green appear yellow, and reddish-blue appears bluish at the peri- 

 phery. Yellow and blue are perceived farther out on the retina than 

 red, and red farther than green. 



Raehlmann'sf investigation was carried through, both with pig- 

 ment and with spectral colors. His results show that red passes over 

 through orange into yellow ; violet becomes blue, and green passes out 

 through yellow, while blue and yellow do not change in tone in indirect 

 vision. He found that yellow and blue have the widest retinal zones, 

 but his data as to the relative extensions of the other color zones is of a 

 most conflicting character. The color limits were found to vary with 

 changing brightness of stimulus and with changing conditions of re- 

 fraction. 



In his earlier paper Raehlmann was inclined to accept the Helm- 

 holtzian principle of explanation, but in his later discussions he rejects 

 this position and explains the phenomena in terms of a lesser degree of 

 illumination at the periphery. 



Raehlmann's third paper attempts to determine and express quan- 

 titatively the relative sensitivity of different parts of the retina to light 

 of different colors. Behind a slit in the ocular of a spectroscope he 

 pivoted a Nicol prism ; the part of the spectrum which served as the 

 stimulus passed through the slit and fell upon this prism, where its 



*Briesewkz. Ueber das Farbensehen bei normalen und atropischen N. 

 Opticus. Inaug. Diss., Griefswald, 1872. 



tE. Raehlmann. Ueber Farbenblindheit ;in den peripherisohen Netzhaut- 

 partien, u. s. w., Inaug. Diss., Halle, 1872; Ueber Verhaltnisse der Ferbenemp- 

 findung bei indirecten und directen Sehen, Graefe's Archiv., XX, i, 1874, S. 15-32; 

 Ueber Schwellenwerte der verschiedenen Spectral fanben an verschiedenen Stellen 

 der Netzhaut., Graefe's Archiv., XX, i, S. 232-254; Daltonismus und die 

 Youngsche Farbentheorie, Graefe's Archiv., XXII, i, S. 29-64; Ueber relativen 

 und absoluten Mangel des Farbensinnes, Berlin, 1900. 



