VII 



RETINAL EXCITATION 



345 



retina due to the protoplasmic movements observed under the 

 ;i< lion of light. 



The contraction of the outer limbs of the rods, described by 

 Angelucci (1884) and his pupils, and the contraction of the inner 

 segments, as observed by Gradenigo (1885), were subsequently 

 disputed by van Genderen-Stort, by Greeff, and 1 >y Chiarini from 

 exact measurement and comparison. According to van Genderen- 



B c 



l-'ic. K.S.- \Vitieal sectii in of irnii>ral half of retina of Leuciacu* auto, fixed in Fli'inmin- s tlni.i. 

 (P Chiarini ) A, at't'-r krei.in- tho animal '-'4 hours in tin- dark; B, at'trr exposing it I'm 

 G hours in direct sunlit-lit ; C. alt.-, ,'xiisin- it for 5 hours in <lin-ct sunlight, and subs,- 

 (juently for 1 hour in total ilarkni'-s. 



Stort, Greeff, and Chiarini, when a frog is exposed to light the 

 inner limbs of the rods merely suffer a passive change of form, 

 due to pressure from the ellipsoidal bodies of the cones which 

 approach the external limiting membrane (Fig. 169). 



Another important fact was discovered by Engelmann (1885), 

 who found that the movements of the cones and pigment-cells of 

 the retina under light are directly dependent on the nervous 

 system. He saw that when one eye only of the frog was exposed 



