266 PRACTICAL MICROSCOPY. 



purpose. Thin sections of animal tissues are placed in a 

 one per cent, osmic acid solution, and then carefully 

 washed to remove all superfluous acid. They must then 

 be immersed for about twenty-four hours in a solution of 

 one part of oxalic acid to fifteen of water, when after 

 washing they are ready for examination. 



The oxalic acid produces darker or lighter shades (carmine 

 and Burgundy tints) in proportion to the length of time 

 the section has been immersed in osmic acid, but if the 

 tissue has once become blackened, the oxalic solution is 

 powerless to redden it afterwards. 



Chloride of gold solution has been employed for colour- 

 ing nerve-fibres ; a solution in water of one or two grains to 

 the ounce is generally used. The section should be soaked 

 in the solution until it has acquired a straw-coloured tinge, 

 it is then to be washed and placed in a one per cent, solu- 

 tion of acetic acid. In the light the nerve-fibres become 

 coloured a blue or violet tinge in a few hours. Nitrate of 

 silver is a very important agent for the staining of animal 

 tissues. Dr. Lionel Beale writes, " A weak solution may be 

 imbibed by delicate tubes, and part being precipitated in 

 the tube, perhaps as a chloride, or in combination with 

 some albuminous material, subsequently becomes decom- 

 posed by the action of light." 



Recklinghausen, who has employed this plan with much 

 success, uses a very dilute solution, made by dissolving 

 one grain of nitrate of silver in from one to two ounces of 

 distilled water. 



In 1863, Dr. Roberts, of Manchester, used a solution of 

 tannin and magenta for staining the red human blood- 

 corpuscles, and this is a subject which still requires 

 investigation. 



Dr. Beale's carmine fluid for staining all forms of bioplasm 

 of living things is made as follows : 



