MOUNTING FLUIDS, AND METHODS. 85 



XIV. MOUNTING FLUIDS, AND METHODS. 



The fluid chosen will depend on the nature of the tissue and 

 other circumstances. 



1. If a section is to be mounted direct from water, glycerine, 

 Farrant's solution, or glycerine jelly may be used. 



2. If a section is to be mounted in balsam, it must have every 

 trace of water removed by alcohol, and the alcohol must be dis- 

 placed by one of the clarifying reagents xylol, clove-oil, &c. 

 already mentioned. 



Glycerine. Pure glycerine is only used for such tissues as 

 have been previously hardened. In the case of tissues delicate 

 tissues which have not been previously hardened or fixed the 

 direct application of pure glycerine would injure them. In this 

 case, the best way is to mount the object in normal saline, and at 

 one edge of the cover-glass to place a drop of a mixture of equal 

 parts of glycerine and water. Put the preparation in a plate 

 covered by a bell-jar an extempore moist chamber. The glycerine 

 slowly penetrates as the water evaporates. 



Some tissues are rendered too transparent by glycerine, and, 

 moreover, it is very difficult to seal up and keep tight glycerine 

 preparations. 



Glycerine and Formic Acid. This is sometimes used, especially 

 for picro-carmine preparations. It is made by adding formic acid 

 to dilute glycerine (i per cent.). 



Farrant's Solution. This is for many preparations far more 

 serviceable than glycerine, as it does not render some tissues so 

 transparent as glycerine, and the preparations can be easily sealed 

 up or " ringed." 



Preparation (Hamilton's receipt}. Make a saturated solution 

 of arsenious acid in water by boiling. After standing for twenty- 

 four hours filter. Take equal quantities of water, glycerine, and 

 arsenious water, and to the mixture add picked gum-arabic. Let 

 the latter dissolve until a thick syrupy fluid is obtained, which takes 

 about a week at an ordinary temperature;, but it must be stirred 

 frequently. Filter slowly through filter-paper, which must be fre- 

 quently changed. 



Glycerine Jelly. Melt it in hot water, place a drop on the 

 soction, apply a cover-glass, and gently press it down. It gelatinises 

 in a few minute?. 



Canada Balsam. Place some Canada balsam in a capsule or 

 wide-mouthed bottle near a fire or in a warm chamber (65 C.) 

 until it becomes hard. Let it cool. This dry balsam is to be dis- 

 solved in some medium. Some use chloroform, others brn/ol, 

 others a mixture of both, or turpentine as a solvent. In any case, 



