()liSP:RVATIONS OX VISION IN BRIGHTNESS AND IN 

 OBSCITRTTY, WITH A HYPOTHESIS ON THE CAUSE 

 OF COLOR-BLINDNESS." 



Bv (). LuMMr.K. 



A. Ttieory or J. v. Kries.* 



It has long been known that the retinal layer of rods and rones con- 

 stitutes a structure sensitive to light by means of which energetic ini- 

 l)ulses from without excite the optic nerve. AMiile investigations 

 concerning acuity of vision appear to warrant the conclusion that 

 the cones alone suffice for sight, yet the anatomical structure of the 

 rods, closely resembling as it does that of the cones, indicates that 

 they, too, play a part in seeing. Recent physiological researches on 

 vision under feeble illumination and on the influence of the visual 

 l)urple in the rods upon the perception of color have rendered it more 

 antl more possible to distinguish between the parts played by thest^ 

 two kinds of retinal organs.' 



As a basis for (he investigation we take the theory of Von Kries, 

 which holds that the cones are a color-perceiving '" brightness ai)])a- 

 ratus,"' the rods a color-i)lind "darkness aj)paratus.*" According to 

 this theory the cones are ada|)ted for vision under high illumination, 

 and their excitation by light waves produces in the brain the sensa- 

 tion of color, while the rods with their visual purple are insensitive 

 to color, become acti\(' only in dim light, and are able to nnich in- 

 crease their sensitiveness in the dark. You Kries calls this peculiai*- 

 ity of the rods '" adajition to obscurity"" | Dunkeladajjlation |. Be- 

 fore the cones react to coloi- the rods convey to the brain the impres- 

 sion of colorless light. 



o Translated by iHM'iiiission from VerlnuKllunjjen tier Deutsclu'ii Physikali- 

 sehen Gesellscliaft. Brvmswick. ^'l : li. llMik 



& J. V. Kries. I'ber die Funktioii der NetzliaulstiilK-iicn. Z. S. f. I'sycli. u. 

 Pbys. d. Slnncsrogane. 9. 81-12:',. I8!»4. 



c See A. Koiiig. I'bcr dcii ."Mciisclilicbcii Seb|»iU"])ur uiid s«>ine Hcdeutuni; itt^iiii 

 yeheu. Sitzber. d. Berl. Akad. d. W'isseiiseb., p. 577, 18iJ4. 



249 



