HARDENING AND FIXING REAGENTS. 



FOR general histological and pathological work, the harden- 

 ing agents usually employed are Alcohol and the Bichro- 

 mate solutions. The others are only used for special applications. 



Alcohol will not penetrate well pieces larger than a cubic 

 inch, while the Bichromates are applicable to material of any 

 size. 



If rapid hardening is required, Alcohol, Erlicki's Fluid, or 

 Klein's Fluid is employed, but the two latter have a tendency 

 to make the tissues brittle if they remain in the solution too 

 long. 



A relatively large quantity of hardening fluid, about 20 

 times the bulk of the object to be hardened, should always be 

 used, and the pieces should be as small as circumstances will 

 allow. It is best to suspend the object near to the top of a 

 tall vessel filled with the fluid, which is accomplished by 

 placing the pieces of tissue on absorbent wool enclosed in 

 a muslin bag, but this is not always considered to be neces- 

 sary. The pieces can simply be placed in a bottle with the 

 fluid, which should be circulated from time to time, and 

 changed when necessary. 



As soon as the objects are sufficiently hard they should be 

 removed from the hardening solution and placed in 70 p. c. 

 Alcohol till required. 



Of the special fixing agents Osmic Acid is the best, more 



