THE CORNEA. 257 



water, floated on to a slide, removed from the water, 

 and covered, glycerine being afterwards added at 

 the edge of the cover-glass. To prevent the latter 

 from pressing on the softened tissue, two narrow 

 slips of thin glass, which may be cut with a writing 

 diamond, are to be placed one on either side, before 

 placing the cover-glass over. 



Preparation 14 and 15. The cell-spaces of 

 the cornea. These are shown in two ways ; by the 

 silver method, and by the method of puncture injec- 

 tion. 



The demonstration of the cell-spaces by the silver 

 method may be attempted in the cornea of the frog. 

 The animal is decapitated and the brain destroyed. 

 The eyelid is then removed, and the eye having been 

 made prominent by the pressure of the thumb in 

 the manner previously recommended, the epithelium 

 is scraped off the front of the cornea with a sharp 

 scalpel. The cornea is then rubbed with a stick of 

 fused nitrate of silver (lunar caustic). After live 

 minutes the surface is thoroughly washed with a 

 stream of distilled water from a wash-bottle. The 

 head is now placed in spirit in the light ; in a short 

 time (from a few minutes to an hour), when the 

 cornea is browned, the vessel containing it is re- 

 moved from the window and left in a dark place for 

 twenty-four hours. The cornea is then sliced off, 

 placed in water, where any remaining patches of 

 epithelium are now removed, slit in a triradiate 

 manner, so that it may lie flat on a slide, and finally 

 mounted in glycerine. 



The cornea of mammals may be prepared with 

 silver in a similar manner, but, being generally 

 thicker than in the frog, it is necessary to allow the 

 caustic a longer time to penetrate, and, in the final 

 preparation, to prepare sections parallel to the 

 surface, instead of mounting the cornea whole. 



To inject the cell-spaces of the cornea by the punc- 

 ture method, the eye of the pig or guinea-pig may 



be used, if a human eve is not procurable for the 



go* 



