ON THE MECHANISM OF THE EYE. 



597 



with intricate calculations, that few have 

 attempted to develope it: he groundeil the 

 whole on an experiment borrowed from Bar- 

 row, which, with me, has totally failed ; and 

 I cannot but agree with Dr. Olbers in the 

 remaris, that it is easier to confute him than 

 . to understand him. He argued for a partial 

 change of the figure of the lens; and per- 

 haps the opinion was more just than the rea- 

 «ons adduced for its support. Lobe, or ra- 

 ther Albinus *, decidedly favours a similar 

 theory ; and suggests the analogy of the 

 lens to the muscular parts of pellucid ani- 

 mals, in which he says that even tlie best 

 microscopes can discover no fibres. Cam- 

 per also mentions the hypothesis with consi- 

 derable approbation •]■. Professor Reil pub- 

 lished, in 1793, a Dissertation on the Struc- 

 ture of the Lens ; and, in a subsequent pa- 

 per, annexed to the translation of my for- 

 mer Essay in Professor Gren's Journal J, he 

 discussed the question of its muscularity. I 

 regret that I have not now an 0[)portunity of 

 referring to this publication ; but I do not 

 recollect, ihat Professor lleil's objections are 

 different from those which 1 have already no- 

 ticed. 



Considering the sympathy of the crystal- 

 line lens with the uvea, and the delicate na- 

 ture of the change of its figure, there is lit- 

 tle reason to expect, that any artificial sti- 

 mulus would'be more successful in exciting 

 a contractive action in the lens, than it has 

 hitherto been in the uvea ; much less would 

 that contraction be visible without art. Soon 

 after Mr. Hunter's death, I pursued the e.x- 



• De quibusdam Oculi Partibus, L. B. 1746. Ap. Hall. 

 Disp. Anat. IV. 301. 



f De Oculo Huraano, L. B. ] 74a. Ap. Hall. Disp. Anat. 

 VH. ii. 108, 109. 



J 1794. 35a, 354. 



periment which he had suggested, for ascer- 

 taining how far such a contraction might be 

 observable. My apparatus (Plate 11. ^Fig. 

 91.) was executed by Mr. Jones. It con- 

 sisted of a wooden vessel, blackened within, 

 which was to be filled with cool, and then 

 with warmer water: a plane speculum was 

 placed under it ; a perforation in tlie bottom 

 was filled with a plate of glass; proper rings 

 were fixed for the reception of the lens, or 

 of the whole eye, and also wires for trans- 

 mitting electricity : above these, a piece of 

 ground and painted gla.ss, for receiving the 

 image, vvas supporlect by a bracket, which 

 was moved by a pinion, in connexion witii 

 a scale divided into fiftieths of an inch. With 

 this apparatus I made some experiments, 

 assisted by Mr. Wilkinson, whose residence 

 was near a slaughter house : but we could ob- 

 tain, by this method, no satisfactory evi-- 

 dence of the change ; nor was our expecta- 

 tion much disappointed. I understand also, 

 that another gentleman, a member of this 

 Society, was equally unsuccessful, in at- 

 tempting to produce a conspicuous change 

 in the lens by electricity. 



X. In man, and in the most common qua- 

 drupeds, the structure of the lens is nearly si- 

 milar. '1 he number of radiations is of little 

 consequence ; but I find that, sometimes at 

 least, in the human crystalline, there are 

 ten on each side, (Plate 12. Fig. 93.) not 

 three, as I once, perhaps from a too hasty 

 observation, concluded *. Those who find 

 any difficulty, in discovering the fibres, must 

 have a sight very ill adapted to microscopi- 

 cal researches. I have laboured with the 

 most obstinate perseverance to trace nerves 

 into the lens, and 1 have sometimes iraa- 



• De Corp. Hum. Vir. Cons. 08. 



