AND HOW TO USE IT. 237 



Indigo-Carmine:— Oxalic acid, i part ; distilled water, 22 to 30 

 parts ; indigo-carmine as much as the solution will take up. If 

 the blue colour is in excess, it may be removed with a solution of 

 oxalic acid in alcohol. It tinges rapidly and uniformly, and is 

 recommended for colouring axis cylinders and nerve-cells of brain 

 and spinal cord previously hardened in chromic acid (Thiersch). 



Carmine. — This is a useful stain, but it tires the eye. There 

 are several ways of making this stain, of which the following are 

 a few : — 



{a) Take 2 grms., and rub thoroughly in a mortar with a few 

 drops of water ; then add 4 cc. liq. ammonia and 48 cc. distilled 

 water ; filter into a bottle, which should be left unstoppered for a 

 day or two for the excess of ammonia to evaporate. This is a 

 strong solution, which must be diluted before using (Klein). 



{b) Beale's Carmine Solution. — Dissolve carmine, i grm., in 

 liq. ammoniae fort. 3 cc, warm, add distilled water, 120 cc, 

 and filter. Then add glycerine, 30 cc, and rectified spirit of 

 wine, 120 cc, and keep in a well-stoppered bottle. 



(c) Borax Carmine. — Thoroughly mix carmine, 2 grms., and 

 borax, 8 grms., in a mortar, dissolving in warm water for twenty- 

 four hours. The supernatant fluid, which must be decanted, is 

 then ready for use. All carmine-stained preparations, after being 

 thoroughly washed in water, are improved by placing them for a 

 few minutes in a i per cent, solution of acetic acid. This bright- 

 ens the colour, and fixes the carmine in the nuclei, and also 

 differentiates the stained from the unstained parts. Thus the 

 stain becomes more selective. 



{d) Borax-Carmine (Arnold's). — A saturated solution of borax 

 is prepared in a wide-mouthed bottle. The borax should be in 

 some excess. Carmine is now added to the solution under con- 

 stant agitation, until after a while it no longer dissolves, and an 

 excess remains at the bottom of the vial, mingled with the crystals 

 of borax. After twenty-four hours the supernatant fluid is de- 

 canted. To this clear portion 2 fluid ounces of alcohol and i 

 fluid drachm of caustic soda solution are added (U.S.P.) The 

 staining solution is now ready, or the alcohol may be omitted 

 (Arnold), and the liquid evaporated to dryness. The red amor- 



