HISTOLOGY OF THE LENS. 369 



macerating fluids into detached drops of various sizes (hyaline 

 drops), but partly also into a finely granular or structureless 

 mass. This breaking-up occurs also spontaneously after death, 

 and inasmuch as it chiefly affects in the first instance the 

 extremities of the fibres, it is intelligible that the products of 

 the breaking up must principally accumulate in the stellae 

 of the lens. Hence these products were formerly held to be 

 normal constituents of the lens. Moreover, under certain cir- 

 cumstances, vacuolse form in the fibres, and their borders then 

 appear just as though they had been eroded. The deeper the 

 fibres lie, that is, the nearer the centre, the more resistant do 

 they become, and the less are they acted on by reagents. 



Authors usually admit the existence of a sheath to the fibres 

 of the lens, and call them by another name, to wit, lens tubules. 

 But it is a matter of great difficulty to demonstrate the 

 presence of this sheath, especially in the extremely thin 

 dentated fibres of Fishes, and the grounds on which authors 

 found their statements are still more untenable than those 

 which are advanced to prove the presence of a membrane in 

 the blood corpuscles. The presence of longitudinal and trans- 

 verse stride in the fibres of the lens has also been maintained ; 

 but this striation is so rarely visible, and presents so many 

 irregularities, and so much variability in its arrangement, that 

 no conclusions can be drawn from it in regard to the minute 

 structure of the fibres, and they should rather be looked upon 

 as accidental wrinklings and irregularities. 



Mineral acids, alcohol, and the act of boiling cause the fibres 

 of the lens to become hazy, whilst their contours are rendered 

 more distinct. This depends on the circumstance that their 

 principal chemical constituents are of an albuminous nature ; 

 consisting, in fact, chiefly of globulin, with a certain quantity of 

 albuminate of potash, and ordinary ser-albumen. Other mate- 

 rials that have been ascertained to enter into the composition 

 of the lens fibres are a little fat, with traces of cholesterine, 

 about one half per cent, of ashes, and sixty per cent, of water. 

 The qualitative characters, no doubt, vary with the layer from 

 which the fibres are taken ; for, apart from the fact that the 

 central fibres are more resistant, the nucleus of the lens 

 becomes much harder than the superficial layers under the 



VOL III. B B 



