CORALLIN — CYANIN 295 



days; the sections are then placed on a shde in a drop of a 0.5 

 per cent, solution of ferrous sulphate; after a few minutes the 

 sections are washed in water, then in alcohol, and are finally 

 treated with a drop of glycerine and examined under a cover- 

 glass. This gives an insoluble brown precipitate with tannins. 



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 alcohbl, and the whole 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 over- 

 stain 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 cellulose. When sections 

 are placed in it for some time and are then rinsed with ammonia 

 and finally with distilled water, crystals of cellulose arc precipi- 

 tated 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 



