I 3 o PRACTICAL HISTOLOGY. 



are seen dividing into fibrils, and these forming a network 

 without even when examined with very high powers any 

 apparent connection with surrounding tissue. The nerve 

 fibrils have almost always a beaded appearance. 



236. Crystalline Lens (H.) Fibres of lens of cod 

 fish boiled for ten minutes in dilute sulphuric acid (i per 

 cent). Dissociate with needles and preserve in Farrants' 

 solution. The serrations of the fibres are very distinctly 

 seen. The lens of the ox, cat, or rabbit may be prepared 

 in the same manner, but the serrations are not nearly so 

 well marked. 



237. Examine a. (L.) T. S. lens hardened in absolute 

 alcohol. The laminae of fibres are readily seen. 



b. (H.) T. S. fibres of lens hardened in chromic acid 

 and spirit ( 13), showing their hexagonal shape. 



238. Hexagonal Pigment Cells (H.) With the point 

 of a scalpel scrape off some of the pigmentary layer inside 

 the choroid of an eye hardened in chromic acid and spirit, 

 13, and place the scraping in a drop of Farrants' solution. 

 Cover, and examine. The hexagonal cells, each with a clear 

 nucleus, will be readily seen. 



239. Retina. Methods. a. The retina may be well 

 prepared for section in the chromic acid and spirit fluid, as 

 mentioned in 13. The sections may be unstained or 

 stained with dilute carmine ( 318, a) and preserved in 

 Farrants' solution or in glycerine. 



b. The retina may also be well hardened by osmic 

 acid. It is placed in a \ per cent solution for thirty-six 

 hours, and then washed in distilled water for twenty-four 

 hours or so. Sections are preserved in Farrants' solution, 

 or in a saturated solution of potassium acetate. Osmic 

 acid is the best agent for showing the general form and 

 connections of the rods and cones. These may be isolated 

 by teasing sections made by freezing, as described below, 

 or more simply by means of scissors. 



c. The gold method is very useful (W. Stirling) for 

 facilitating the cleavage of the outer segments of the rods 

 transversely into their plates, as described by Max Schultze. 

 The posterior half of the eyeball of a frog is placed for an 



