CONTENTS. ix 



i 



SECTION VI. 



THE STRUCTURE OF THE KETINA. 



PAGE 



737. The optic nerve 1193 



738. The Layers of the Ketina 1194' 



739. The Neuroglial Elements 1195 



740. The Nervous Elements. The rods and cones with the rod fibres 



and cone fibres 1197 



741. The inner nuclear layer 1200 



742. The layer of ganglionic cells and layer of optic fibres . . . 1202 



743. The probable connection of the several elements .... 1202 



744. The Macula Lutea and Fovea Centralis 1204 



745. The blood vessels of the retina 1205 



746. The Pigment Epithelium 1206 



SECTION VII. 

 ON SOME GENERAL FEATURES OF VISUAL SENSATIONS. 



747. The relation of the sensation to the intensity of the stimulus ; 



Weber's law - 1209 



748. The relation of the sensation to the duration of the stimulus . . 1212 



749. Flickering and continuous sensations 1213 



750. Sensations produced by various changes in the retina referred to 



some external source of light 1214 



751. Localisation of visual sensations 1215 



752. The conditions of discrete visual sensations 1217 



753. The region of distinct vision. The limits of distinct vision . . 1218 



754. Nature of the discreteness of visual sensations ; retinal visual units 1219 



SECTION VIII. 

 ON COLOUR SENSATIONS. 



755. The existence of many kinds of Colour Sensations .... 1222 



756. The mixing of Colour Sensations 1223 



757. The several usual Colour Sensations result from the mixture of 



simpler, primary sensations 1224 



758. The conditions which determine the characters of Colour Sensations 1226 



759. Complementary Colours 1227 



760. Any Colour Sensation produced by the suitable mixture of three 



Colour Sensations 1228 



761. The Young-Helmholtz theory of Colour Sensations .... 1229 

 762. Bering's theory of Colour Sensations. A comparison of the two 



theories 1231 



b 2 



