THE CORNEA. 251 



the thin glass. Oil of cloves is then allowed to run 

 under and clarify the specimen, which is prevented 

 from curling up, in consequence of the pressure of 

 the cover-glass. 



Preparation 8. Epithelium of the cornea, 

 The stratified epithelium covering the front of the 

 cornea is well seen in the vertical sections, but the 

 characters of the individual cells which compose it 

 must be studied in a teased preparation. For this 

 purpose a piece of the cornea is placed in a compara- 

 tively large quantity of J- per cent, bichromate of 

 potash solution, and allowed to remain in this for a 

 week, changing the fluid once or twice during that 

 time. Then with the point of a scalpel, or spear- 

 headed needle, a small portion, including however 

 the whole thickness of the epithelium, is scraped off 

 the front, placed in a drop of distilled water on a 

 slide, and broken up with needles as finely as pos- 

 sible. A piece of hair is added, and lastly the 

 cover-glass, and the specimen is then ready for ex- 

 amination. The cells of the various layers will be 

 recognized by the characteristic forms they present ; 

 those of the deepest layer being in shape like a rifle- 

 bullet, those next above cupped to receive the 

 rounded or conical ends of the deeper cells, and the 

 superficial layers being more flattened as they are 

 nearer the surface. The fine ridges and furrows on 

 many of the cells can be distinctly made out with 

 a high power, and give a jagged contour to the cell. 



To preserve the preparation permanently in glyce- 

 rine it should first be stained with logwood. This 

 is readily done by applying a drop of a very weak 

 solution to the edge, and allowing it to diffuse under 

 the cover-glass; after a short time glycerine is added 

 at the same edge, and gradually replaces the log- 

 wood solution, the water from which evaporates 

 meanwhile at the other borders of the cover-glass. 



Preparation 9. The substantia propria of 

 the cornea, The fibrous structure of the sub- 

 stantia propria of the cornea can readily be seen by 



