THE CORNEA. 255 



compressing it. Then the cornea, iris, and lens are 

 removed together, after cutting round the sclerotic 

 with scissors, and are placed in salt solution, and 

 finally the iris and lens are removed in the same way 

 as in the preceding preparation, and the cornea is 

 immersed in gold solution. Since it is much thicker 

 than the frog's cornea, it should remain in the chlo- 

 ride of gold which does not penetrate very rapidly 

 a full hour and a half, after which it is placed in 

 acidulated water in the light, and otherwise treated 

 in the same way as the frog cornea. But as it is 

 not so easy to separate the mammalian cornea into 

 lamellae, it is better after four days to place the 

 stained cornea in spirit for twenty-four hours, when 

 thin sections parallel to the surface may be cut, and 

 mounted in glycerine. Embedding in wax-mass is 

 not necessary if the cornea is held in the left hand, 

 and allowed to rest over the end of the forefinger, 

 the razor being directed from the operator. 



Preparation 12. Isolation of corneal cor- 

 puscles. After the corneal corpuscles and nerves 

 have been stained with gold in this way, they can 

 be isolated by dissolving away the intermediate 

 substance by caustic alkali, the action being arrested 

 before the corpuscles and nerves, which are more 

 resisting than the connective tissue bundles, are 

 are also destroyed. With this object a part or the 

 whole of a gold-stained cornea whether of frog or 

 mammal is placed, divested of epithelium, in a 

 watch-glass containing a strong (20 per cent.) solu- 

 tion of caustic potash or soda, and this is then put 

 into a warm chamber at 40 C. At the expiration 

 of three-quarters of an hour the tissue, which is now 

 quite soft and pulpy, is removed with a section lifter, 

 and placed in a vessel containing a large quantity 

 of water faintly acidulated with acetic acid. Small 

 portions may then be taken up and mounted, with 

 or without further breaking up, in glycerine. The 

 corpuscles are beautifully displayed, forming a con- 



