xxxiv CONTENTS. 



PACE 



^ 532. Emmetropic, myopic, hypermetropic, and presbyopic eyes . . 840 

 §533. The changes observed in the eye during accommodation . . . 850 



SECTION III. 



The Mechanism of Accommodation and the Movements of 



the Pupil. 



§ 534. The mechanism for changing the anterior curvature of the lens . 854 

 § 535. The evidence that such a mechanism does effect the result . . 856 



The Changes in the Pupil. 



§ 536. Circumstances leading to constriction and to dilation of the pupil . 857 



§ 537. Constriction and dilation 858 



§ 538. The nerves supplying the pupil 859 



§ 539. Constriction a reflex act by means of the optic and oculo-motor 



nerves 860 



§ 540. Changes in the pupil through the action of the cervical sympathetic 



nerve 862 



§ 541. The nature of the dilating mechanism 863 



§ 542. Direct action of drugs and other agencies on the pupil . . . 86V> 



§ 543. The nervous mechanism of accommodation 868 



§ 544. The association of the movements of accommodation and the move- 

 ments of the pupil 868 



SECTION IV. 



Imperfections in the Dioptric Apparatus. 



§ 545. Imperfections of accommodation 870 



^ "'46. Spherical aberration 871 



§ 547. Astigmatism 871 



§ 548. Chromatic aberration 873 



§ 549. Entoptic phenomena 874 



SECTION V. 

 On Soke General Features of Visual Sensations. 



§ 550. The relation of the sensation to the intensity of the stimulus ; 



Weber's law 878 



551. The relation of the sensation to the duration of the stimulus . . 8-1 



|j 552. Flickering and continuous sen.-at inns 883 



S3. Sensations produced by various changes in the retina referred to 



some external source of light 883 



§ 554. Localisation of visual sensations 885 



§ 555. The conditions of discrete visual sensations 886 



§ 556. The region of distinct vision. The limits of distinct vision . . 887 



§ 557. Nature of the discreteness of visual sensations ; retinal visual units 889 



