ORGANS OF THE SENSES. 507 



interior ; it is this external and firmer portion which exhibits 

 the lamellar arrangement so generally described, the fibres 

 following a less regular course internally, and being separated 

 by wider intervals. 



The tissue of the cornea has been recently described as a 

 peculiar modification of the w r hite fibrous element of the 

 schlerotic. It would appear, however, that the fibrous tissue 

 of which it is constituted is of a kind totally distinct from 

 that which enters so largely into the composition of the cornea 

 proper ; a conclusion derived from its examination, for which 

 we might be prepared, simply by the consideration of the 

 very opposite physical characters of the two parts, the schle- 

 rotic and cornea, the former being white and opaque, and the 

 latter clear and diaphanous. 



If we tear up with needles a small portion of the schlerotic, 

 and examine it with the microscope, we then see that it is 

 made up, for the most part, of bundles of wavy and distinct 

 fibres, presenting scarcely a nucleus, and reflecting a yellowish 

 hue ; if now we carry our examination still further, and apply 

 acetic acid to these bundles, they swell up, the fibres be- 

 coming indistinct, and finally converted into a jelly-like 

 substance. 



On the other hand, if we submit a portion of the cornea 

 to the same examination, and the same treatment by acetic 

 acid, we shall encounter different appearances and results. In 

 the first place, we shall not perceive distinct and separate 

 bundles of fibrous tissue free from nuclei, but we shall merely 

 notice an indistinct fibrous character in the mass, with here 

 and there elongated nuclei imperfectly seen ; on the applica- 

 tion of acetic acid, however, the fibres become much more 

 evident, and multitudes of nuclei are brought into view. 

 Thus, then, it is evident that the tissue of the cornea is some- 

 thing more than a modification of the white fibrous element 

 of the ,schlerotic. The nucleated fibres just described are 

 often, in the neighbourhood of the nuclei themselves, ex- 

 panded and membraneous ; and it is remarkable that they do 

 not lie in direct apposition with each other, but interlace in 

 such a manner as to describe elongated spaces, several of 



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