1 6 COLOR SENSITIVITY OF THE PERIPHERAL RETINA. 



green, and blue light which appears red in direct vision, is seen as green 

 " when we direct the eye away from it and cast a sidelong glance at it." 

 ' The cause of this is the yellow spot, which acts somewhat as a piece 

 of yellow glass would do, absorbing certain kinds of light more than 

 others." 



Landolt* experimented with a modified form of the Foerster peri- 

 meter, employing colored papers as stimuli. As the accompanying table 

 shows, he obtained a much wider area of color sensitivity than any of 

 his predecessors had done. 



Here, as in all other tables of this paper, the limits of the color-zones are referred to the 

 meridians (or, more correctly, to the half-meridians) of the retina. Thus the " out meridian " 

 of the table here appended indicates the temporal half of the horizontal meridian of the retina, 

 *. e., the retinal meridian which runs outward or temporalward from the fovea. In view of the 

 inversion of the spatial relations which occurs when objects are imaged upon the retina, it 

 will be seen that if the retinal positions be designated by the names of those positions in the 

 visual field which correspond to them, the opposite relations will hold and opposite names must 

 be employed. What we have here called the "out" meridian (of the retina) would then be 

 called the " in " meridian (of the visual field) its position in the field of vision would lie inward 

 or nasalward from the visual axis. 



In these experiments, blue and yellow were perceived almost to the 

 extreme limits of the field of vision ; then follow in order, orange, red, 

 yellow-green, blue-green, and violet. But Landolt remarks that with a 

 sufficiently bright stimulus all colors are recognized at the periphery. 



The following color changes, which Landolt observed with differ- 

 ent degrees of eccentricity of stimulus, are similar to those which had 

 been reported by preceding investigators : Blue-green and violet pass 

 through bluish to gray ; yellow-green and orange pass through yellow ; 

 red through yellowish-red or brown and yellowish, while blue and 

 yellow undergo no change save decrease of saturation. 



Landolt finds an analogy between the phenomena of indirect vision 

 and those of direct vision with faint illumination. No part of the nor- 

 mal retina is wholly insensitive to color of any tone ; the term color-blind 



*E. Landolt. II perimetro e la sua applicazione, Annali d'Ottalmologia, 

 1871, pp. 465-484; Farbenperception der Netznautperipherie, Zehender's Klinische 

 Monatsblatter fur Augenheilkunde, XI, 1873, S. 376-577. De la perception des 

 couleurs a la peripherie de la retine, Annales d' Oculistique, LXXI, 1874, pp. 44-45. 

 Papers by Landolt are also ito be found in the Sitzungsbericht der Ophthalmolo- 

 gischen Gesellschaft, 1873, and in Graefe und Saemisch's Handbuch der Gesamm- 

 ten Augenheilkunde, III, 1873. 



