S22 OBSERVATIONS AND EXPERIMENTS ON VISION.* 



and that their size was little affected by the quantity of light 

 ■which passed through them. At first, I thought that their 

 dilatatiou was occasioned by a defect of sensibility in the re- 

 tinas; but I was quickly obliged to abandon this opinion, 

 as the patient assured me, that his sensation of light was as 

 strong, as it had ever been during any former period of 

 his life. I next inquired, whether objects at different dis- 

 tances appeared to him equally distinct. He answered, that 

 he saw distant objects accurately, and in proof told me 

 what the hour was, by a remote public clock ; but he added, 

 that the letters of a book seemed to him so confused, that 

 it was with difficulty he could make out the words which 

 they composed. He was now desired to look at a page of 

 a printed book through spectacles with convex glasses. He 

 did so, and found that he could read it with ease. From 

 these circumstances it was very plain, that this gentleman, 

 at the same time that his pupils had become dilated, and his 

 upper eye-lids paralytic, had acquired the sight of an old 

 man, by losing suddenly the command of the muscles by 

 which the eye is enabled to see near objects distinctly; it 

 being known to those, who are conversant with the facts 

 relating to human vision, that the eye in its relaxed state is 

 fitted for distant objects, and that the seeing of near ob* 

 jects accurately is dependent upon muscular exertion. 

 Another in- The disease of which I have spoken is perhaps not ex- 



sianee, tremely rare. For having related the preceding instance of 



it to Mr. Ware, a fellow of this society, he was kind 

 enough shortly after to send to me a young woman, who 

 appeared to be likewise affected with it. But as I saw 

 her only once, and had not then sufficient time to examine 

 her case minutely, I speak with diffidence concerning its 

 nature. 

 Effectofthe II. After I had reflected frequently upon these cases, it 



juice of bella- occurred' to me, that, as the juice of the herb belladonna, 

 donna on the , ' , ' ''. , ., ,.. 



eye when applied to the eye, occasions the pupil to dilate con- 



siderably, and to become unalterable by light, an effect 

 > might at the same time be produced by it upon vision, si- 



milar to that which I have just described. I had, indeed, 

 in the course of a few years immediately preceding, ap- 

 plied belladonna several times to my own eyes, without ob- 

 .1 serving 



