OP>SERVATTONS OX VISION IN BRIGHTNESS AND IN 

 ()P>S('rKr] Y. WITH A HYPOTHESIS ON THE (VVUSE 

 OK ( H )L()R-BLINI)NESS.« 



Bv (). LlMMER. 



A. Theory of J. v. Kries.'' 



It has long been known that the retinal hiyer of rods and cones con- 

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

 pulses from without excite the optic nerve. AA'hile 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 reseuihliug as it does that of the '-ones, indicates that 

 they, too, play a pai't in seeing. Hecent physiological researches on 

 vision under feeble illumination and on the influence of the visual 

 purple in the rods u[)on the ])(>rception of coloi- have rendered it more 

 and more possil)le to distinguish between the parts i)layed by these 

 two knids of retinal organs.'' 



As a basis for the investigation we tak'e the theory of \"on Kries, 

 which holds that the coues are a color-perceiving '' brightness appa- 

 ratus." the rods a (•oh)i'-i)bii(l '' darkness apparatus." According to 

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

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

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

 to color, become active only in dim Hght, and are able to nnich in- 

 crease their sensitiveness in the dark. Vim Kries calls this peculiar- 

 ity of the rods ''adaption to obscurity*" | Dunkeladaptat ion |. Be- 

 fore the cones i-eact to coloi- tlic rods convey to the l)rain the iuipr'*^- 

 sion of colorless lialit. 



"Translated l)y iierniissioii from Nerliandhuisoii dci- I )<'ntscli('ii IMiysikali- 

 Kchen 'viesellseliaft, Bruiiswick. \'l : :.'. I'.idt. 



''.I. V. Ki-ies. I'licr die L'linktidii (U'v Nctzli.iutstiiliclicii. /. S. f. I's.vdi. u. 

 Pliys. d. .Sinnesro^jaiu'. i», Sl-12:!. iS'.M. 



c See A. Koiiig, tlber deu Aleiischliclieii SehjiMrpur uiid seine lledentnim heini 

 Seheu. Sitzber. d. Berl. Akad. d. Wisseiisch., p. 577, US'.M. 



249 



