244 THE MICROSCOPE AND HOW TO USE IT. 



Metallic Staining Solutions. 

 Nitrate of Silver. — A solution of from i to 4 grains of the 

 nitrate to an ounce of distilled water, is much used for fresh 

 tissues. In staining the mesentery, it is merely necessary to 

 immerse it for two or three minutes, and then expose it to the 

 light in distilled water for two or three days. The water should 

 be changed several times. The whole mesentery may be 

 removed with the intestine and stained in silver, and then hard- 

 ened in spirit. Some portions will then be found to be stretched 

 out naturally, and these can be cut out and mounted in Canada 

 balsam and benzole. 



Osmic Acid, i per cent., may be further diluted as required. 

 It blackens fat and the medullary sheath of nerves. It is useful 

 for hardening the internal ear. 



Chloride of Gold, J per cent, solution. Place a small quan- 

 tity of the solution in a watch-glass, and immerse the tissue, 

 which must be perfectly fresh in it. Let it remain in the dark for 

 from half-an-hour to an hour or more ; place in distilled water, 

 which must be changed several times, and expose to diffused 

 daylight until it becomes a violet-brown, which will take about 

 twenty-four hours in, summer. The tissue, if it is small, can be 

 mounted in glycerine. 



Chloride of Gold and Lemon-Juice.— Ranvier is in the habit 

 of demonstrating the corneal nerves by using lemon-juice, in 

 which the tissue is left for five minutes. Then it is soaked for 

 fifteen to twenty minutes in 3 cc. of i per cent, solution of gold 

 chloride, and finally for twenty-five to thirty minutes in distilled 

 water, to which one or two drops of acetic acid have been added. 

 It must then be exposed to the sun until the fibres become dis- 

 tinct. Formic acid is also used with gold. 



Staining with Osmic and Oxalic Acids.— Little pieces of fresh 

 or freshly-dried preparations are left for an hour in a i per cent, 

 solution of osmic acid ; then carefully washed and soaked in a 

 cold, saturated solution of oxalic acid ; and finally examined in 

 water or glycerine. Elastic fibres are stained yellow and fat 

 black, while the walls of capillaries and many connective-tissue 

 substances are stained red. 



