vin OCULAE MOVEMENTS 427 



These facts show that the retina is not necessary to the 

 production of the phenomenon we are discussing, and that the 

 central nervous organs alone may be concerned in the genesis of 

 visual phantasms, which are the only cerebral visual images 

 really known to us. 



The most interesting and least common visual hallucinations 

 are those of persons, perfectly sound in mind and body, who 

 have the faculty on closing their eyes of seeing visions that 

 are perfectly comparable with the images of real objects. Cardano, 

 Goethe, and Johannes Miiller possessed this power. 



" In 1828," writes Miiiler, " I had occasion to discuss with 

 Goethe this subject, which was equally interesting to us both. 

 As he knew that when I lay down quietly with my eyes closed 

 images readily shaped themselves before me though I was not 

 actually asleep, since I was quite able to observe the figures, he 

 was very curious to know how these images were formed in my 

 mind. I told him my will had no influence on the production 

 or on the changes of those figures. . . . Goethe, on the other 

 hand, was able to choose the subject at will, but the changes then 

 developed, apparently involuntarily, but in regular and sym- 

 metrical order. Here is the difference in the two natures the 

 one endowed with a wealth of poetical imagination in the highest 

 degree, the other directed to the investigation of reality and of 

 natural processes." 



X. Secure elsewhere within the bony walls of the orbit, the 

 eye is protected in front by the lids, which are able to close 

 rapidly, in order to keep out excess of light, or to lessen the 

 effect of sudden mechanical shocks. 



According to Exner the hairs of the eyebrows and eyelashes 

 are the most sensitive organs of the whole body. Their importance 

 in the protection of the eye is therefore obvious; the eyelashes 

 are peculiarly adapted to prevent the penetration of dust particles 

 from the air into the conjunctival sac ; the hairs of the eyebrows 

 apart from their importance in expression keep the perspiration 

 of the forehead away from the eyes, and moderate the action of 

 the light rays from above. The lashes are continually lubricated 

 by the secretion of the adjacent Meibomian glands which open 

 near their bulbs. 



The eyelids close automatically and remain closed during 

 sleep; they also shut reflexly in the waking state to external 

 stimuli. Winking may be caused by stimulation either of the 

 optic or of the trigeminal nerves ; the reflex is always bilateral, 

 even when the stimulus acts only on one eye unilateral winking 

 is f normally a purely voluntary action. This is the case not only 

 in men and apes but also in carnivora (dogs, cats) ; on the other 

 hand, in herbivora (rabbits, guinea-pigs) and in birds and 

 amphibians (frog) reflex winking either by the lids or by the 



