4r HARDENING AND FIXING REAGENTS. 



placed in it from 6 to 12 hours, and then transferred to 90 p. c. 

 Alcohol until hardened. When the hardening is completed, 

 transfer the tissue to 70 p. c. Alcohol till wanted. 



(iii.) CHROMATE OF AMMONIUM. 



5 p. c. aqueous solution. 



Especially useful for delicate cell structures, as parenchyma 

 of secreting cells. Tissues are placed for 48 hours in this 

 reagent, thoroughly washed in Distilled Water and passed 

 through diluted to strong Alcohol. 



(iv.) BICHROMATE OF AMMONIUM. 

 BICHROMATE OF POTASSIUM. 



2 to 5 per cent, aqueous solution of either. 



Simple Bichromate solutions are sometimes preferred to 

 Miiller's Fluid for hardening parts of the central nervous 

 system, but opinions vary as to their greater usefulness even 

 for this purpose. A two per cent, solution should be used to 

 start with and changed after 24 hours and again after 3 

 days, and then once a week for the next 6 weeks, increasing 

 the strength by one per cent, each week till it reaches five per 

 cent. In this way an entire brain may be hardened thoroughly 

 and satisfactorily in 8 weeks. 



After hardening for a month in Miiller's Fluid, it is often 

 advantageous to finish the process by a fortnight's immersion 

 in five per cent. Bichromate solution. 



(iv.) MULLER'S FLUID. 



Bichromate of Potassium, 2 grms. ; Sulphate of Sodium, 

 1 grm. ; Water, 1 00 cc. 



A good hardening reagent for delicate structures where 

 the process is required to be gradual. It is well adapted for 



