CORNEA. 295 



623. Papillae Foliatae of the Rabbit (HERMANN). See 

 wiss. Mik., v, 4, 1888, p. 524. 



623a. Olfactive Organs of Vertebrates (Doom, Arch. f. mik. 

 Anat., 1887, p. 74). 



624. Cornea. Impregnation with gold and with silver is 

 indispensable in the study of the cornea. 



Negative images of the corneal cells are easily obtained by 

 the dry silver method (KLEIN). The conjunctival epithelium 

 should be removed by brushing from a living cornea, and the 

 corneal surface well rubbed with a piece of lunar caustic. 

 After half an hour the cornea may be detached and examined 

 in distilled water. 



' In order to obtain positive images of the fixed cells the 

 simplest plan (RANVIER) is to macerate a cornea that has 

 been prepared as above for two or three days in distilled 

 water. There takes place a secondary impregnation, by 

 which the cells are brought out with admirable precision. 



The same result may be obtained by cauterising the cornea 

 of a living animal as above, but allowing it to remain on the 

 living animal for two or three days before dissecting it out, 

 or by treating a negatively impregnated cornea with weak 

 salt-solution or weak solution of hydrochloric acid (His). 



But the best positive images are those furnished by gold 

 chloride. RANVIER prefers his lemon-juice method to all 

 others for this purpose, see 209. It is important that the 

 cornea should not remain too long in the gold- solution, or the 

 nerves alone will be well impregnated. 



Ranvier also recommends this method as being the best for 

 the study of the nerves. 



ROLLETT (Strieker's Handbuch, p. 1115) recommends a 

 double impregnation with silver followed by gold for obtaining 

 gold-stained negative images. A cornea having been treated 

 for a short time only with 0'5 per cent, silver nitrate solution, 

 and the silver reduced, is treated with 0*5 per cent, gold- 

 chloride solution. The brown stain of the silver disappears 

 immediately the preparation is placed in the gold- solution ; 

 after a few minutes the preparation is exposed to the light in 

 acidulated water. Reduction of the gold rapidly takes place, 

 and in the place of the former brown stain of the silver the 

 ground-substance shows the well-known blue of reduced gold 



