REAGENTS AND PROCESSES 535 



then in alcohol, and are finally treated with a drop of glycerine and examined under 

 a cover-glass. 



An alcoholic solution of copper acetate, to which has been added a small amount 

 of acetic acid and glycerine, is used to demonstrate glucose in position within the 

 cells where it occurs. The sections are laid in a mixture of the above solution, and 

 an equal volume of sodium hydrate in alcohol, which is brought to boiling on the 

 water-bath. Since glucose is insoluble in alcohol, the cuprous oxide which indicates 

 the presence of glucose in this reaction is found to be deposited within the cells 

 which contain the sugar. For other tests for sugar with a salt of copper see 

 Fehling's Solution. See under Resin in next chapter. 



Corallin. This stain is to be dissolved in a 30 per cent, or a saturated solution 

 of sodium carbonate. It is particularly useful in staining the callose of sieve tubes. 

 It is best to overstain the sections and then to reduce the intensity of the color by 

 immersing the sections in a 4 per cent, solution of sodium carbonate. 



Corrosive Sublimate. See Fixatives. 



Cuprammonia. This should be freshly prepared as needed in the following 

 manner: Put copper filings into a bottle or flask, which is provided with a ground- 

 glass stopper. Pour concentrated ammonia upon the filings and rock back and 

 forth. Only sufficient ammonia should be used to cover the filings. When the 

 solution will dissolve cotton, it is ready for use. This reagent is a solvent of cellu- 

 lose. When sections are placed in it for some time and are then rinsed with ammo- 

 nia and finally with distilled water, crystals of cellulose are precipitated within the 

 cells which are stained blue with chloroiodide of zinc, and red with Congo-red. The 

 crystals are again dissolved on the addition of cuprammonia. 



Cyanin. This stain is almost insoluble in water, and should be dissolved in 

 50 per cent, alcohol. This is a useful stain for fats and all ethereal oils. Sections 

 of fresh material, or material fixed in an aqueous fixative, such as an aqueous solu- 

 tion of corrosive sublimate or picric acid, will be sufficiently stained when left in the 

 cyanin solution for about half an hour. Overstaining may be reduced with glyc- 

 erine. The alcoholic solution of cyanin, to which has been added an equal bulk 

 of glycerine, is a good stain for suberized membranes, particularly after the sec- 

 tions have been treated with eau de Javelle, which destroys the tannins and pre- 

 vents the lignified membranes from taking the stain. When sections are placed 

 in a dilute solution of cyanin, say 20 drops of a concentrated alcoholic solution 

 of cyanin in 100 mils of water, and are then washed in alcohol and placed in oil 

 of cloves containing eosin, the lignified and suberized walls will be stained blue, 

 while cellulose walls will be red. The sections may then be mounted in Canada 

 balsam. When sections are placed for a quarter of an hour in a concentrated 

 alcoholic solution of cyanin, and are then washed in alcohol and transferred for a 

 quarter of an hour to a 5 per cent, ammoniacal solution of Congo-red, the lignified 

 membranes will appear blue, while the unlignified membranes will appear red. 

 After washing in alcohol, such sections may be mounted in Canada balsam. 



Dahlia. An aqueous solution of from o.ooi per cent, to 0.002 per cent, is used 

 for staining live nuclei. The dividing nuclei of Tradescantia virginica, for instance, 

 when kept in this stain for a few hours, become weakly stained. The structure of 

 pyrenoids is well demonstrated by fixing them in equal parts of a 10 per cent, solu- 

 tion of potassium ferricyanide and a 55 per cent, solution of glacial acetic acid and 

 then staining with dahlia, and finally swelling the pyrenoids somewhat in a weak 

 solution of potassium hydrate. 



Dammar Lac. Dammar lac is dissolved in equal parts of benzol or xylol and 

 turpentine; the solution is filtered and evaporated to the desired consistency. This 

 is used as a mounting medium the same as Canada balsam; it has a lower refractive 



