7 8 PRACTICAL HISTOLOGY. 



stained black as " silver lines," and they may be mounted in 

 glycerine or balsam, either unstained or after staining with logwood, 

 picro-carmine, or other dye as desired. 



In order to stain the lining endothelium of the vascular system, 

 a solution of silver nitrate is used. The special precautions 

 required are referred to in the text. (Lesson on Blood-Vessels.) 



4. Golgi's Method. In this method parts of the central nervous 

 system hardened in potassic bichromate are treated for many days 

 with silver nitrate or mercuric chloride to demonstrate the processes 

 of nerve-cells. (Lesson on Nervous System.) 



5. Nitrate of Silver and Osmic Acid (Golf/i). This is specially 

 useful for the nervous system. Place a fresh nerve of a rabbit just 

 killed in 



Potassic bichromate (2 per cent.) . "* .10 parts 



Osmic acid (1 per cent.) . . . 2 ,, 



for an hour ; tease the nerve, and let it remain in the mixture for 

 another hour. Transfer for 8 hours to .5 per cent, silver nitrate and 

 then to alcohol. 



B. Gold Chloride. 



Gold Chloride. This substance has rendered particular service, 

 especially in connection with the terminations of nerves. It is used 

 as \-2 per cent, watery solution. Various methods are employed, 

 according to the end desired. 



1. Acetic Acid Method. Place a small piece of perfectly fresh 

 tissue, 2 mm. cubes, e.g., hyaline cartilage or a small cornea, in i per 

 cent, solution in a glass thimble for half-an-hour, keeping it in the 

 dark all the time. These small glass thimbles are particularly use- 

 ful, and are better to be somewhat broader relatively than those 

 shown in fig. 26. The tissue will become yellow ; wash it 

 thoroughly in distilled water, and expose it to bright daylight in 

 distilled water slightly acidulated with acetic acid. In a day or 

 two it will become of a purplish or violet-brown colour. Sections 

 can then be made and mounted in glycerine. 



2. Loewit's Method. To one part of formic acid (sp. gr. 1.16) 

 add two parts of distilled water. Place small pieces of the fresh tissue 

 (1-2 mm. in thickness), e.g., tendon from a rat's tail, in this mixture 

 for J-i minute, until they become somewhat transparent; transfer 

 them to a glass thimble or watch-glass containing i per cent, gold 

 chloride for 15-20 minutes, i.e., until they have become yellow 

 throughout. During this process, the tissue should be exposed to 

 light as little as possible. Place the tissue in formic acid (i 13), 

 and keep it in the dark for twenty-four hours. Afterwards place it 

 for twenty-four hours in pure formic acid, and keep it also in the 



