6 HAKDENING AND FIXING REAGENTS. 



quent washing in Alcohol, tissues should be kept in the 

 dark. 



The other Bichromate solutions may be used with Spirit in 

 the same way. 



(iv.<?) ERLICKI'S FLUID, 



Bichromate of Potassium, 5 grms. ; Sulphate of Copper, 

 I grm. ; Water, 200 cc. This solution hardens quicker than 

 " Miiller," and is used in much the same way. 



It is sometimes stated that this solution should always be prepared freth 

 when required, but this is not necessary as it undergoes no change. 



This is the best fluid for hardening large organs quickly. 

 It will harden a spinal cord in 10 days, and is the most suit- 

 able fluid for human embryoes. 



It tends to render the tissues brittle, and also gives the 

 sections a greenish tinge. 



(y.) CHROMIC ACID. 



10 p. c. aqueous solution is kept for stock ; for use it is 

 diluted with 20, 30, or 50 times its bulk of Water, accord- 

 ing to the consistence and size of the tissue. The larger or 

 firmer the tissue the weaker the solution. 



The pieces to be hardened must not be larger than J cubic 

 inch ; the fluid must be changed every day for the first 3 days, 

 and then every third day. Tissues are hardened in from 1 to 

 14 days, according to their nature and size; they are then 

 well washed in Water and kept in 70 p. c. Alcohol in a dark 

 place to avoid deposits. 



Chromic Acid is energetic, but it does not penetrate well, 

 and it makes the tissues brittle. Tissues thus hardened are 

 not well stained by Carmine ; Hsematoxylin or Safranine 

 should be used. 



