EYE. 



199 



Fig. 123. 



The mode in which these fibres are laterally 

 iniitril to each other is equally curious. Sir 

 l'a\ id llrewster says that he ascertained this in 

 looking at a bright light through a thin lamina 

 of the lens of a cod, when he observed two 

 faint and broad prismatic images, situated in a 

 line exactly perpendicular to that which joined 

 the common coloured images. Their angular 

 distance from the central image was nearly five 

 times greater than that of the first ordinary 

 prismatic images, and no doubt whatsoever 

 could be entertained that (hey were owing to a 

 number of minute lines perpendicular to the 

 direction of the fibres, and whose distance did 

 not exceed the ^dth of an inch. Upon ap- 

 plying a good microscope to a well-prepared 

 lamina, the two fibres were found united by a 

 series of teeth exactly like those of rack work, 

 the projecting teeth of one fibre entering into 

 the hollows between the teeth of the adjacent 

 one, as in jig. 124. 



Fig. 124. 



I have said that the lens consists of an outer 

 case or capsule totally different from the solid 



body lonuiiiiil \\itliin it. This capsule is 

 strong, elastic, and prrftvtly tr;iii-,|ii-m. In 

 ihc |M|>er to winch I have alluded in the Me- 

 dico-Chirurgical Transactions, I gave the fol- 

 lowing detailed description of its nature and 

 properties: 



" The real nature of the capsule of the lens 

 has not, I think, been sufficiently attended to; 

 its thickness, strength, and elasticity, have cer- 

 tainly been noticed, but have not attracted that 

 attention which a fact so interesting, both in a 

 physiological and pathological point of view, 

 deserves. That its structure is cartilaginous, I 

 should conclude, first, from its elasticity, which 

 causes it to assume a peculiar appearance when 

 the lens has been removed, not falling loose 

 into folds as other membranes, but coiled in 

 different directions ; or if the lens be removed 

 by opening the capsule behind, and with- 

 drawing it through the vitreous humour, allow- 

 ing the water in which the part is immersed to 

 replace the lens, the capsule preserves in a 

 great degree its original form, especially in the 

 eye of the fish ; secondly, from the density and 

 firmness of its texture, which may be ascer- 

 tained by attempting to wound it by a cataract 

 needle, by cutting it upon a solid body, or 

 compressing it between the teeth ; thirdly, from 

 its permanent transparency, which it does not 

 lose except on the application of very strong 

 acid or boiling water, and then only in a slight 

 degree ; maceration in water for some months, 

 or immersion in spirit of strength sufficient to 

 preserve anatomical preparations, having little 

 or no effect upon it. If the lens be removed 

 from the eye of a fish dressed for the table, the 

 capsule may be raised by the point of a pin, 

 and be still found almost perfectly transparent. 

 This combination of density and transparency 

 gives the capsule a peculiar sparkling appear- 

 ance in water, in consequence of the reflection 

 of light from its surface, resembling a portion 

 of thin glass which had assumed an irregular 

 form while soft ; this sparkling I consider very 

 characteristic of this structure. The properties 

 just enumerated appear to me to distinguish it 

 from every other texture but cartilage ; still, 

 however, it may be said that cartilage is not 

 transparent, but even the cartilage of the joints 

 is semi-transparent, and, if divided into very 

 thin portions, is sufficiently pellucid to permit 

 the perception of dark objects placed behind 

 it, and we obtain it almost perfectly transparent 

 where it gives form to the globe of the eye, as 

 in the sclerotic of birds and fishes. If the soft 

 consistence, almost approaching to fluidity, of 

 the external part of the lens, be considered, the 

 necessity of a capsule capable itself of pre- 

 serving a determinate form is obvious. If the 

 lens were enclosed in a capsule such as that 

 which envelopes the vitreous humour, its sur- 

 face could not be expected to present the ne- 

 cessary regular and permanent curvature ; nor 

 could we expect that if the form of the lens 

 were changed, it could be restored without thu 

 provision of an elastic capsule." 



The capsule is liable to become opaque and 

 constitute cataract, as the body of the lent it. 

 These capsular cataracts are easily distinguiblvttj 



