BY DR. KLEIN. 53 



form tins operation without injuring the substance of the cornea. 

 Thereupon the caustic is two or three times lightly rubbed over 

 the whole surface, after which the eye is washed with saline 

 solution, and the animal is left to itself for twenty or thirty 

 minutes. The cornea is then excised, washed in ordinary 

 water for several minutes, and pencilled with a camel-hair 

 brush. The mode of preparation is as before, care being taken 

 to make one or two radial incisions, in order that the mem- 

 brane may lie flat on the glass surface. After the preparation 

 has been exposed for a few hours, the contrast between the 

 spaces and the yellowish-brown interstitial substance becomes 

 very obvious. v 



[The endothelium of Descemet's membrane, with its dark 

 interstitial lines, brownish-yellow cell substance, and clear 

 ovoid or lobed nuclei, is well seen. It is to be noted that all 

 preparations of this kind must be kept in the dark.] 



Similar results are obtained by the use of the nitrate of 

 silver in solution. With this view the epithelium is either 

 pencilled oft' from the anterior surface with warm water, or 

 scraped off as above described. The cornea is then imme- 

 diately excised and immersed for fifteen or twenty minutes in 

 a half to one per cent, solution. It is then washed and pre- 

 pared as above. If, however, after washing the preparation 

 for a very short time, it is transferred to a ten per cent, solu- 

 tion of chloride of sodium for five or ten minutes, and is then 

 again washed in ordinary water and mounted in glycerin, the 

 appearance is very different. We have before us in most parts 

 the canalicular system marked out by a dark precipitate, while 

 the interstitial substance remains almost clear. In other parts 

 there are gradations of staining between this appearance and 

 the negative staining obtained by the ordinary method. 



Preparation of the Cornea with Chloride of Gold. 

 The fresh cornea of a frog or mammal is placed in as much 

 half per cent, solution of pure chloride of gold as is sufficient 

 to cover it, and left immersed until it acquires a straw-yellow 

 color i. e., at most thirty minutes. Thereupon it is trans- 

 ferred to distilled water, or water slightly acidulated. The 

 preparation passes through pale gray, then dark gray, violet 

 gray, violet and reddish, to dark red the time required for the 

 production of the last-mentioned color differing, caeterisparilmx, 

 according to the time during which it was immersed, and the in- 

 tensity of the light. In the height of summer, twenty-four 

 hours, or even less time, is sufficient ; but in winter several days 

 are required, in which case it is preferable to use distilled, rather 

 than acidulated, water, because the latter is apt to produce too 

 much swelling of the preparation. From a darkly colored 

 cornea so prepared, the anterior epithelium is removed by strip- 

 ping it off from the annulms conjunctivx inwards, with the aid 



