TISSUES OF THE BODY. 



221 



and Engelmanri) (1), has a thickness of from 0'0068-0'0090 mm. in man. 

 It is soluble in boiling water. It is, however, by no means sharply de- 

 lined against the tissue of the, 

 cornea lying underneath. The 

 second layer (c), which bears 

 the name of the membrane of 

 Demours and Descemet, and is 

 0-006-0-008 mm. in the cen- 

 tral portions, and '01-0 '01 2 

 at the border (H. Muller), is 

 separable in various ways from 

 the cornea. It has a consider- 

 able amount of elasticity, so that 

 it rolls up upon itself on loosen- 

 ing. At its circumference it is 

 lost on the anterior aspect of the 

 iris, as the ligamentum petiin- 



atum iridis. Tow, between 



a 



these two transparent mem- 

 branes is found the true tissue 

 of the cornea (a), which has 

 been the subject of such ex- 

 tended research, and whose 

 structure is still far from being 

 satisfactorily elucidated. It 

 is formed of intercellular mat- 

 ter and a system of canals con- 

 taining cells. The first is con- 

 tinuous peripherally with the 

 fibrillated connective-tissue of 

 the conjunctiva, but also, and to 

 a greater extent, with that of 

 the sclerotic. 



This ground-mass of the cor- 

 nea presents transparent, flat 

 bands of 0'0282-0'0090 in 

 breadth, and 0'0045-0'0090 

 mm. in thickness, which are, 

 for the most part, so arranged 



in respect to the surface, that a regularly laminated structure is the result, 

 though, at the same time, a crossing of the bands may be remarked 

 frequently enough, especially on the anterior surface and periphery of the 

 cornea. Owing to the fact that those can be demonstrated either as 

 hanging together in lamella? or separable one from the other, the cornea 

 has been declared at one time to be laminated, at another to be fibrous, 

 or both at once, as a combination of both views. As far as we know at 

 present, the cornea may be likened to a compressed network of ilat bands, 

 matted in layers, a view which is farther borne out by its double refracting 

 properties with polarised light (His}. Reagents, as, for instance, perman- 

 ganate of potash, employed by JRollett, or a 10 per cent, solution of com- 

 mon salt, by Schweigger -Seidel, show it to be made up of the finest fibrilla; 

 however, held together by a homogeneous intermediate substance, which 

 mav also be recognised on fresh corneal tissue, and, better still, in that 



Fig. 215. The cornea of the infant in vertical section, 

 but much shortened, a, corneal tissue; b, anterior; c, 

 posterior transparent htyer; d, laminated scaly epithe- 

 lium ; e single layer of epithelial cells. 



