l8 COLOR SENSITIVITY OF THE PERIPHERAL RETINA. 



intensity was regulated at will by rotating the latter. From that setting 

 of the prism at which the color of the stimulus was just recognized, it 

 was possible to calculate the minimal luminosity of stimulus required 

 to produce the sensation of color. * The following table, which has been 

 compiled from Raehlmann's results ( Schwellenwerte, u. s. w., S. 249), 

 shows the rate at which the retinal sensitivity to the various colors de- 

 creases in indirect vision : 



Lamanskyf also correlates the phenomena of indirect vision with 

 Purkinje's phenomenon. His investigation, already referred to, con- 

 vinces him that the retina is less sensitive to red than to any other color. 

 Hence it is but natural that the sensitivity to red should be the first to 

 be lost in indirect vision, in twilight vision, and in pathological condi- 

 tions of the retina. 



KrtikowJ was a pupil of Woinow, and in general confirmed the 

 results of his master. For stimuli he employed three sizes of squares 

 of red, green, and blue paper ; these he moved out from the visual axis, 

 before a light and a dark background. He found that red and green 

 pass over into yellow before becoming colorless, while blue undergoes 

 no change of tone. The color zone of blue is widest and that of red is 

 narrowest. These zones are fixed and invariable; their limits are in- 

 fluenced neither by the area of the stimulus nor by the brightness of 

 the background. Kriikow accepts the Helmholtzian explanation of his 

 results (i. e,, the partial color-blindness of the peripheral retina), but 

 admits that the possibility of sensing yellow at parts of the retina where 

 sensitivity to red and to green is lacking, is difficult for the Helmholtzian 

 hypothesis to explain. 



*Un fortunately tihis method does not take into account the widely different 

 brightnesses (and saturations) of the different parts of the spectrum. The results 

 obtained in -experiments with different color tones are therefore not expressed in 

 terms of a common standard of brightness (or saturation). They are, for that 

 reason, valueless as a means of comparing the retinal sensitivity to the various 

 color tones. The same objection may be urged against .the work of Lamansky, 

 Dobrowolsky, Mandelstamm, and Cattell. 



tS. Lamansky. Ueber die Grenzen der Bmpnndliichkeit des Auges fur Spec- 

 tralfarben, Graefe's Archiv., XVII, I, 1871, S. 123-134. The same paper also 

 appears in Poggendorff's Annalen, CCXIX, 1871, S. 633-643. 



^Krukow. Sur la sensation 'des couleurs a la peripherie de la retine, Disser- 

 tation, Moscow, 1873 ; Objective Farbenempfrndung auf den peripherischen Theilen 

 der Netzhaut, Graefe's Archiv. XX, i. 1874, S. 255-296. 



