REAGENTS AND MOUNTING MEDIA. 487 



Molybdcde of ammonia. Dissolved in a concentrated solution of ammonium 

 chloride. 



Mordants, for fixing stains; an account of the use of is found on p. 111. 



Mounting fluid. See Enclosing fluid, Canada balsam, Gum dammar, Glycerine- 

 jelly, Glycerine, etc. 



N. 



Nigrosine (Quality I. of Trommsdorf). Watery solution. 

 Picric. To a saturated watery solution of picric acid, a small quan- 

 tity of watery solution of nigrosine is added till the fluid appears a 

 deep olive-green colour. Exceedingly good for unicellular and 

 filamentous algse, staining and fixing at the same time (twelve to 

 twenty-four hours). Also as a double stain for lignified and un- 

 lignified membranes. See p. 111. 



Nitric acid. Used in xantho-proteid reaction (q.v.\ and for maceration. 



Olive oil. Sometimes used as a temporary mountant. See pp. 33, 52. 



Orange G. A good nuclear dye. Used for nuclear figures in saturated 

 aqueous solution. 



Orcin.. In alcoholic solution this is used as a reagent for inuline. See. p. 69. 



Osmic acid, 1 or 2 per cent. Must be kept in darkness, and in a well-closed 

 bottle. Colours oil-drops brown. Instantaneously fixes living 

 protoplasm, and hence serves in nuclear studies. In a mixture of 

 9 parts 0-25 per cent, chromic acid solution, and 1 part 1 per cent, 

 ogmic acid, filamentous algae, Nitella, etc., can be at the sume time 

 hardened and stained. See also Flemming's Fluid (Chromosmium 

 acetic acid), and footnote on p. 444 for decolorising after. 



P. 



Paraffin. Used as an embedding material for sectionising. See p. 445. 

 Paraffins of melting points 45 C. and 52 C. respectively are re-, 

 quired. For some purposes harder paraffins with melting point up 

 to 58 are useful. 



Pasteur's Fluid. See p. 289 for preparation. 



Phenol. See Carbolic acid. 



Phloroglucin. Alcoholic (or watery) solution, 1 to 5 per cent., or even so 

 low as T V per cent will do. Followed by hydrochloric acid, is the 

 best reagent for lignin. See pp. 78 and 134. Phloroglucin is expen- 

 sive, but a convenient substitute can be prepared from cherry-wood. 

 See Cherry-wood extract. 



Picric acid. Saturated watery solution. A good fixing fluid, but requires 

 very careful washing out, especially before using logwood as a stain. 

 Can be dissolved in sea-water for fixing marine algae. 

 akohol. Picric acid dissolved to saturation in 50 per cent, alcohol 



