COLOR SENSITIVITY OF THE PERIPHERAL RETINA. 21 



lasts throughout if the stimulus be of very slight intensity. Both 

 Landolt and Charpentier hold that color vision is the joint product of a 

 two-fold physiological process. One of these processes has its seat in 

 the retina and is relatively simple and primitive in character. The 

 other is cerebral and is of a more highly developed nature. The cere- 

 bral process comes about more readily in proportion to the number of 

 times its nervous apparatus has been called upon to function. The 

 lesser sensitivity of the periphery is to be explained in terms of less 

 frequent functioning, *. e., of relatively defective training. 



Treitel* employed squares of white and colored paper, which he 

 moved in towards the fixation-point upon a perimeter. He found that 

 white has the widest retinal zone; then follow blue, red, and finally 

 green. From the results of a second experiment, which consisted in 

 exposing red, green, and blue squares of different sizes at various parts 

 of the visual field, Treitel concluded that the peripheral retina is least 

 sensitive to green and most sensitive to blue ; and that sensitivity to all 

 colors decreases towards the periphery. He fails to find a satisfactory 

 explanation of these phenomena, but is inclined to refer them to the 

 retina rather than to the optic nerve proper, or to the brain. 



Donders'sf method consisted in obtaining color equations for 

 peripheral regions of the retina. He found that the peripheral retina 

 (about 40 from the fovea on the temporal side) functions very much 

 like the foveal region of the green-blind eye. Red, orange, yellow, and 

 green here appear alike ; nor can blue, indigo, and violet be distinguished 

 from one another. With certain degrees of saturation and brightness 

 of stimulus, however, the specific color tone of each appears, but only 

 lasts for an instant. 



Bonders is of the opinion that no part of the periphery is color- 

 blind. It was he, by the way, who first suggested to Landolt that all 

 colors can be perceived upon the outermost regions of the retina if only 

 the stimulation be sufficiently intensive. But he believes that the color 

 sensitivity of the periphery is so weak as to approximate in some degree 

 the condition of the dichromatic, or even of the monochromatic retina. 

 The periphery possesses a " color sense " which is simply less highly 

 developed than that of the fovea. 



*Th. Treitel. Priifung des Gesichtsfelds mit Pigmentfarben, Inaug. Diss., 

 Konigsberg, 1875 ; Ueber das Verhalten der peripheren und centralen Farben- 

 perception bei Atrophia nervi optici, Konigsberg, 1875 ; Ueber den Werth der 

 Gesichtsfeldsmessung mit Pigmenten fur die Auffassung der Krankheiten des 

 nervosen Sehapparats, Graefe's Archiv., XXV, 2, 1879, 8.29-130,3, S. i-iio; Ueber 

 das Verhalten der normalen Adaptation, Graefe's Archiv., XXXIII, 2, 1887, S. 

 73-112; Ueber den Licbtsinn der Netzhautperipherie, Graefe's Archiv., XXXV, 

 i, 1889, S. 50-75. 



tF. C. Bonders. Ueber Farbensysteme, Graefe's Archiv., XXVII, I, 1881, 

 S. 155-223; Noch einmal die Farbensysteme, Graefe's Archiv., XXX, I, 1884, 

 S. 15-90. 



