250 PRACTICAL HISTOLOGY. 



Miiller's fluid. To obtain it a small piece of the 

 sclerotic is pinned to a cork or wax-cake under weak 

 spirit (equal parts of water and spirit) ; and the 

 lamina fusca is dissected oft' from its inner surface, 

 and floated on to a slide, the spirit being then al- 

 lowed to evaporate so as to leave the delicate mem- 

 brane moistened only with water. The preparation 

 may now be covered, and glycerine added at the 

 edge of the cover-glass. 



Preparation 77 Sections of cornea, The seve- 

 ral layers of which the cornea is composed, and their 

 relative thickness, should first be studied in sections 

 made vertically to its surfaces. For this purpose 

 the anterior part of an eye (pig's or ox's if a human 

 eye is riot procurable) is placed in 2 per cent, solu- 

 tion of bichromate of potash for fourteen days. 

 (Miiller's fluid may be used instead, but, for the 

 cornea, possesses no advantage over the simple bi- 

 chromate, although, if the retina is to be examined, 

 Mailer's fluid should be employed.) It is as well to 

 remove the lens so that the solution passes freely to 

 the posterior surface of the cornea. After the time 

 specified the tissue is put into weak spirit for twenty- 

 four hours, and then transferred to strong spirit. 

 In two or three days more it will be ready for mak- 

 ing sections. For this purpose a piece of the cornea 

 is cut out and embedded in wax-mass. Very thin 

 sections vertical to the surface are to be made, 

 stained in logwood, and mounted in dammar. In 

 this process a source of difficulty is sometimes met 

 with, in the curling up of the posterior part of the 

 section when transferred from spirit to oil of cloves, 

 after having been stained. This can sometimes be 

 got rid of without spoiling the section, by careful 

 manipulation with needles ; but, if it be found im- 

 possible to obviate it in any other way, the plan 

 may be adopted of placing each section, after it has 

 as usual been stained with logwood, and rinsed in 

 water, in absolute alcohol for a few minutes, trans- 

 ferring it to a slide, and immediately covering it with 



