CORNEA. j 05 



fibra arcuata. Note the edges of these lamellae seen in section. In the ground-substance 

 which separates two adjoining lamellae, there exists a series of lacunae or cell-spaces of 

 irregular branched form, which communicate freely by means of fine channels with lacunae in 

 the same plane, and also with the lacunae lying above and below them. This is the lymph- 

 canalicular system of V. Recklinghausen. Each lacuna contains a nucleated cell-plate or 

 corneal corpuscle, which does not completely fill the space, so that lymph and colourless blood- 

 corpuscles can move between it and the wall of the space. These corpuscles are seen as flat, 

 narrow, nucleated, stained spindles lying between the lamellae in oval spaces, which they do 

 not fill completely. Each corpuscle sends processes into the canaliculi, so that they anasto- 

 mose to form a network. They cannot be seen in this preparation ; it requires the use of 

 gold chloride to show their processes satisfactorily (p. 105). 



The posterior elastic lamina is a structureless elastic membrane with sharply defined 

 margins, which stains of a deep yellow tint with picrocarmine. It may become detached, 

 when it curls up. It consists of fibrils. Study the single layer of polyhedral, nucleated, 

 granular, endotlielial cells on its posterior surface (membrana Descemeti). 



CORNEA-CORPUSCLES, AND NERVES OF THE CORNEA. 



PREPARATION. These are both demonstrated by the same method, viz. the gold method. 

 This may be accomplished in several ways. 



(a) Reduction by Dilute Acetic Acid. Remove the cornea from an animal just killed (e.g. 

 cat, rabbit, or guinea-pig), using the same precautions to avoid stretching it as indicated at 

 'p. 104. Place it in a few c.c. of a half per cent, solution of gold chloride, and keep it in the 

 dark. Let it remain in the gold for half an hour to an hour in the case of the cornea of a 

 guinea-pig, and an hour and a half to two hours in that of a rabbit. Remove it, and wash it 

 in distilled water, and place it in water slightly acidulated with acetic acid, and expose it to 

 the light until it becomes of a decidedly purplish or slate-grey colour throughout. Make 

 vertical and horizontal sections, and mount them in glycerine. 



(b) Reduction by strong Tartaric Acid. Proceed as before up to the stage where the cornea 

 is washed in distilled water. Expose it for a day, or two days, to the light in distilled water 

 without the addition of any acid, until it assumes a violet colour. Place it in a mixture of 

 glycerine, one part, and water, two parts, for two or three days, and keep it in the dark. 

 Wash, and place it in a small beaker half filled with a nearly saturated watery solution of 

 tartaric acid. Heat this in a water-bath kept about 45 C. until it assumes a deep purple 

 colour, which it does in a few minutes. Make sections vertical and horizontal and mount 

 them in glycerine. 



(c) Reduction with Formic Acid. Place the cornea in the juice of a fresh lemon for five 

 minutes. Wash it well, and transfer it to a one per cent, gold chloride solution for half an 

 hour. Wash it again, and place it in a twenty-five per cent, solution of formic acid for 

 twenty-four hours. It must be kept in the dark until the reduction is complete. This process 

 removes all the epithelium, and is, therefore, not suited for showing the terminations of the 

 nerve-fibrils between the cells of the anterior epithelium, but it shows the nerve-fibrils and 

 corpuscles in the cornea admirably. 



Vertical Section of Cornea. EXAMINATION (L and H). Observe the same general arrange- 

 ment of parts as before, but note the rows of connective-tissue corpuscles, stained of a deep 



p 



