8 HARDENING AND FIXING REAGENTS. 



Tissues ought to be placed in the solution from 1 5 minutes 

 to 2 hours, and then in, 90 p. c. Alcohol to complete the 

 hardening. 



After this the tissues must be washed in 70 p. c. Alcohol ; 

 if Water be used black specks are apt to form. 



The action of the fluid can be accelerated by heating it to 

 38 C. (100-4 P.) 



For glands and glandular structures the following is very 

 useful: Corrosive Sublimate, 10 grins.; Alcohol (70 p. c.), 

 100 cc. ; Glacial Acetic Acid, 1 cc. Small pieces are 

 placed in this for an hour and the hardening completed in 

 Alcohol. 



(vii.) NITRIC ACID (Altmann). 



3 p. c. aqueous solution. Sp. gr. about 1-02. Used as a 

 fixing agent. 



The pieces of tissue must be as small as possible, and placed 

 in the Acid until quite fixed ; this takes from 15 to 30 minutes. 

 Useful for fixing nuclei of cells, embryo es and the retina. 



viii.) OSMIC ACID. 



1 p. c. aqueous solution, which must be carefully preserved 

 from dust, as it is readily reduced (blackened) by small quan- 

 tities of organic matter. This solution is usually kept in the 

 dark. 



Especially useful for delicate structures, when rapid fixing 

 is required. 



For use it is diluted with 4 or 5 times its volume of 

 Distilled Water, or more generally in conjunction with 

 Chromic Acid as in Flemming's and Fol's solutions. Tissues 

 are placed in it from 8 to 10 hours, well washed in Distilled 

 Water, cut, and mounted in Farrant's solution. 



Some authorities prefer to fix with the vapour ; this is done 



