XXXIT.] THE EYE. 369 



the nerve-fibres and the arrangement of the connective tissue. An 

 interstitial injection of osmic acid is a good method for isolating the 

 structural elements. 



15. Blood- Vessels of Eyeball. It is not difficult to inject from 

 the aorta with a carmine-gelatine mass the blood-vessels of the eye- 

 ball of an animal. Select an albino rabbit. Sections are mounted 

 in balsam. One-half of the injected eyeball of an albino rat 

 mounted in balsam shows the connections, distribution, and 

 arrangement of the blood-vessels. 



16. The eyelids. Harden the eyelids of an infant in corrosive 

 sublimate or .25 per cent, chromic acid (3 or 4 days) and then in 

 alcohol, or in alcohol alone. Make sections, vertical to its surface 

 and transverse to its long axis, which must be rather thick, and 

 mounted in balsam to show the general arrangement of the parts. 

 Finer sections are stained in haematoxylin or picro-carmine. Be- 

 sides the sections of hair-follicles, connective tissue, and orbicularis 

 muscle, note the Meibomian glands. 



ADDITIONAL EXERCISES. 



17. Fibrils of Cornea. (a.) Macerate the cornea in lime-water, baryta- 

 water, or dilute potassic permanganate, (b.) A better method is to dry the 

 cornea, make T.S., allow them to swell up in water, and stain with picro- 

 carmine. 



18. Epithelium of Lens. Use a small lens (frog or rat), ami place it for a 

 few minutes in AgN0 3 (i : 300). Expose to light in glycerine, and examine. 

 Note on the anterior surface (.) silver lines bounding polygonal areas cor- 

 responding to the inter-epithelial cement. (J.) Black granular converging lines 

 corresponding to the cement between the crystalline fibres (best seen on 

 posterior surface). 



19. Other Methods for the Retina. By the usual methods of hardening the 

 retina, it is impossible to make out the connections between its several elements. 

 The two methods which have quite recently yielded the best results apart 

 from the direct use of osmic acid are the methods of Golgi and Ehrlich's- 

 mel.hylene-blue method. 



(a.) Golgi's Methods. Ramon y Cayal has made a large number of prepara- 

 tions both by the silver method (p. 344) and the rapid osmico-bichromat", 

 method (p. 345), especially on the retina of birds. In this way he lias shown 

 that the protoplasmic processes of the nerve-cells of the ganglioiiic layer 

 ramify in the inner molecular layer, and end in terminal arborisations in several 

 planes in this layer. Several varieties of nerve-cells with extensive terminal 

 arborisations in the other layers of the retina are also described by him. 

 The following medium method gives good results : 



(1.) Place the retina and sclerotic in weak osmico-biahromate fluid 

 (osmic acid, i per cent.), 2 cc., bichromate of potash (3 per 

 cent.), 20 cc., for 24 hours. 



(2.) Transfer to i per cent, silver nitrate (24 hours). 

 (3.) Auain for 24 hours, as in (i). 

 (4.) Again for 24 hours in silver. 

 33 2 A 



