296 REAGENTS AND PROCESSES 



fats and all ethereal oils. Sections of fresh material, or mate- 

 rial fixed in an aqueous fixative, such as an aqueous solution 

 of corrosive sublimate or picric acid, will be sufiiciently stained 

 when left in the cyanin solution for about half an hour. Over- 

 staining may be reduced with glycerine. 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 

 sections have been treated with eau de Javelle, which destroys 

 the tannins that prevent the 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 c.c. 

 of water, — for ten hours or longer, 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. AVhen 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 mem- 

 branes will appear blue, while the unlignified membranes will 

 appear red. After washing in alcohol and afterward in xylene, 

 such sections may be mounted in Canada balsam. See also 

 page 265. 



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 struc- 

 ture of pyrenoids is well demonstrated by fixing them in equal 

 parts of a 10 per cent, solution 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. 



Decalcification. — Three per cent, of nitric acid in 70 per 

 cent, alcohol is a good decalcifying reagent. The material 

 should be left in the solution for several days. Chromic acid 

 has a decalcifying action; a i per cent, to 2 per cent, solution 



