298 ' THE ESSENTIALS OF HISTOLOGY. 



y. Ranvier's method. Immerse in lemon-juice for 5 to 10 minutes, then 

 wash with water and place in 1 per cent, gold chloride solution for 20 

 minutes. Then treat either as in Cohnheim's or as in Lowit's method. 



16. Staining with nitrate of silver. Wash the fresh tissue with distilled 

 water ; immerse in to 1 per cent, nitrate of silver solution for 5 to 10 

 minutes ; rinse with distilled water and expose to bright sunlight either in 

 water, alcohol, or glycerine. This method is used to exhibit endothelium and 

 generally to stain intercellular substance. 



17. Golffi's nitrate of silver methods. These are chiefly employed for 

 investigating the relations of cells and fibres in the central nervous system- 

 Two methods are mostly used, as follows : 



a. Very small pieces of the tissue which has been hardened for some weeks 

 in bichromate solution or Miiller's fluid are placed for half an hour in the 

 dark in 0*75 per cent, nitrate of silver solution, and are then transferred for 

 24 hours or more to a fresh quantity of the same solution (to which a drop 

 or two of formic acid may be added). They may then be hardened with 50 

 per cent, alcohol, and sections, which need not be thin, are cut either from 

 celloidin with a microtome or with the free hand. The sections are mounted 

 in Canada balsam, which is allowed to dry 011 the slide : they must not be 

 covered with a cover-glass, but the balsam must remain exposed to the air. 



ft. Instead of being slowly hardened in bichromate, the tissue is placed at 

 once in very small pieces in a mixture of bichromate and osmic (3 parts of 

 Miiller's fluid to 1 of osmic acid). In this it remains from 2 to 5 days, after 

 which the pieces are treated with silver nitrate as in the other case. This 

 method is not only more rapid than the other, but is more sure in its results. 



18. 'EhrlicKs methyl-blue method. This method is one of great value for 

 exhibiting nerve-terminations, and in some cases the relations of nerve-cells 

 and fibres in the central nervous system. For its application the tissue must 

 be living : it is therefore best applied by injecting a solution of methyl-blue 

 (4 parts to 100 of saline solution) into the blood-vascular or into the lymphatic 

 system, but good results can also sometimes be obtained by immersing small 

 pieces of freshly -excised living tissue in a less concentrated solution (0*2 per 

 cent.). In either case the tissue must be spread out in a thin layer freely 

 exposed to the air ; the blue colour then appears in the nerve-cells and axis- 

 cylinders, even to their finest ramifications. To fix the stain the tissue is 

 treated for some hours with saturated solution of picrate of ammonia, after 

 which the preparation can be mounted in glycerine. 



Mounting Solutions : 1. Saline solution. A 0'6 per cent, solution of 

 common salt is used in place of serum for mounting fresh tissues for imme- 

 diate examination. 



2. Glycerine, either pure or diluted with water. The cover-glass may be 

 fixed by gold size. 



3. Canada balsam, from which the volatile oils have been driven off by 

 heat, dissolved in xylol. 



