290 REAGENTS AND PROCESSES 



alcohol. This can be prevented by placing the fresh material 

 in alcohol which is acidulated by vapor of sulphuric acid in the 

 following manner: For each 100 c.c. of alcohol several cubic 

 centimeters of concentrated sulphuric acid are poured over 

 ^ gm. of sodium sulphite, and the vapors arising are conducted 

 into the alcohol. This operation need require hardly more 

 than a minute. After twenty-four hours the material should 

 be transferred from the acid alcohol to neutral alcohol. There- 

 after the material will not discolor and will take stains very well 

 when used for histological purposes. 



Calcium Nitrate. — (i) Used to differentiate more clearly the 

 lamellae of starch grains. Potato starch, for instance, is placed 

 in a rather strong aqueous solution of methyl violet. After the 

 grains have become deeply colored, they are treated with a weak 

 solution of calcium nitrate, when the methyl violet becomes pre- 

 cipitated, particularly in the less dense lamellae of the starch 

 grains. (2) Calcium oxalate is precipitated in the form of crystals 

 when sections containing oxalic acid are treated with a solution 

 of calcium nitrate. The calcium nitrate is thus a test for the 

 presence of oxalic acid. 



Canarin. — This is often used as a stain for tissues which 

 have been cleared in caustic potash. Canarin is not affected 

 by this reagent. 



Carbolic Acid (Phenol). — Used as a clearing agent. If 

 leaves which have been hardened and bleached in alcohol are 

 placed in three parts of turpentine and one part of carbolic 

 acid, or in pure carbolic acid, the leaves will become so trans- 

 parent that their cellular structure may be made out from one 

 surface to the other. Pollen grains may be made transparent 

 in the same manner. 



Carmalum, Mayer's. — Carminic acid i gm., alum 10 gm.; 

 dissolve in 200 c.c. of hot d.istilled water; filter and add a few 

 crystals of thymol, or o.i per cent, of salicylic acid, or 0.5 per 

 cent, of sodium salicylate. This stains material well in bulk, 

 with little danger of overstaining. If this happens, it may be 

 corrected by washing with a o.i per cent, solution of hydrochloric 



