334 MANUAL OF HISTOLOGY. 



eric acid solution ; they can then be washed in water and easily 

 picked to pieces. In order to see the arrangement of the fibrillse 

 in the different layers, the cornea of a rabbit should be pricked 

 with a needle in several places ; then some highly infectious 

 fluid, as the exudation in puerperal peritonitis, is to be brushed 

 over the surface, and in a few days an infiltration will have 

 taken place throughout the interfibrillar substance. We shall 

 then see the lines of pus-cells crossing one another in different 

 directions, and sometimes collections of micrococci forming 

 stellate figures. 



A very delicate preparation of the fixed corneal cells may 

 be made by removing a fresh cornea, and then immersing it 

 from three to six hours in aqueous humor, in a moist chamber. 

 In examining it take care, as before mentioned, to avoid any 

 pressure upon the cover-glass. 



It is easier, however, to demonstrate the cells and lymph- 

 spaces by staining with silver or gold. To do this the nictitat- 

 ing membrane of a live frog should be cut off or held to one 

 side by an elevator ; the exposed cornea is then placed near the 

 mouth of a test-tube, in which some water has been raised 

 to the boiling point ; when the epithelium begins to appear 

 opaque it should be carefully wiped off with a fine cloth ; a 

 per cent, aqueous solution of nitrate of silver is then applied ; 

 when the cornea has become thoroughly white by this method, 

 it is to be removed, washed in a weak solution of common salt, 

 placed in distilled water, and exposed to the light until it be- 

 comes brown. It should then be cut at the edges and mounted 

 in glycerine. In ten or fifteen minutes it will be transparent 

 and ready for examination. Instead of removing the epithe- 

 lium by steam, a solution of silver nitrate (-J- per cent.) may be 

 used, the lids being held out of the way until the epithelium 

 appears whitish; this outer layer is then removed, and the 

 same process repeated as before. The substantia propria as- 

 sumes a brown color, and the corpuscles appear as lighter spaces 

 in it. The nuclei may be exposed by hsematoxylon. 



The best preparations, both for the lymph-spaces and the 

 nerves, are made with chloride of gold. A fresh cornea, pref- 

 erably one from a live pigeon, is removed immediately after 

 decapitation and immersed for five minutes in lemon- juice, 

 then washed in distilled water, placed for fifteen minutes in a 

 1 per cent, solution of chloride of gold, again washed, and this 



