382 SENSITIVE SYSTEM. 



resistance, even to the sclerotica ; for neither one texture nor the 

 other are we able to rend with our hands, even with the aid of the 

 forceps. If an incision be made directly across the substance of 

 the cornea, lamina after lamina may be stripped off; and while 

 we are doing this, we cannot but notice that the surface is con- 

 tinually freshly bedewed with a limpid serous fluid oozing from 

 the cellular interstices. This watery exudation, some imagine, 

 is pent up in cells during life, and its escape and diffusion after 

 death is the cause, they conceive, of the filmy obscurity of the 

 cornea, which so speedily follows the extinction of life. If the 

 cornea is macerated, it swells, turns opaque, and becomes soft and 

 flabby ; and in this condition it proves very readily separable into 

 its component laminse, in consequence of their cellular adhesions, 

 which in the recent eye are dense and compact, being now lax 

 and filled with fluid : indeed, the laminse may be felt sliding one 

 over another, by squeezing and rubbing them between the fingers : 

 for all this, however, we cannot correctly determine their 

 number, though we can discover that the anterior layer is 

 evidently continued from the conjunctiva sclerotica^. When 

 closely examined in this softened condition, the laminae 

 shew signs of a fibrous texture ; and the density and tough- 

 ness of the cornea favour this idea, as also does the circum- 

 stance, of its bloodvessels being both small and scarce. In the 

 healthy state the vessels are too minute to admit red blood, 

 though red ones are seen commonly enough under inflammation. 

 Nerves have not been traced into its substance, nor do its laminai 

 appear to be sensible, unless it be the anterior one, which has 

 probably nearly the same feeling as other parts of the conjunc- 

 tiva : this (coupled with the vascularity) is a strong fact to shew 

 their identity. Since, then, this is a part that possesses such 

 firmness of texture and mechanical resistance, we must consider 

 that it was made so tough to complete the eye-case or defence in 

 front; at the same time, from being transparent, it is perfectly 

 permeable to light, and, as such, is also operative in the produc- 

 tion of vision. 



Iris. 



The iris (so denominated from the brilliancy of its aspect and 

 variety of its tints) is that part from the appearance of which is 

 vulgarly assigned the colour of the eye. In order to examine this 

 body we must excise the cornea, behind v,'hich it is perpendicu- 

 larly extended, after the manner of an internal eyelid, for the 

 purpose of regulating the quantity of light going to the bottom of 

 the eye. Its boundary edge being fixed within the peri|jhery 

 just behind the cornea, they both necessarily exhibit the samt' 



