LIST OF REAGENTS. 461 



PEEENYI'S FLVID. 



Preparation. — Dissolve 1'5 grm. chromic acid crystals in about 

 half a litre of water. Add 40 c.c. strong nitric acid. 

 "When cold add 300 c.c. 90 per cent, alcohol (methylated 

 spirit), and make up to 1 litre with water. The solution 

 becomes violet-coloured. 



Vso. — Hardening reagent, especially useful for embryos. 

 Tissues after remaining in the flviid 2-4 hours should be 

 washed in 70 per cent, alcohol. 



PICRIC ACID, saturated solution. 



Preparation. — Saturate water with picric acid by shaking it 

 up with the crystals. Allow to stand : decant before use. 

 Use. — Hardening reagent. Wash out with alcohol. 



PICRIC ACID, Kleinenberg's solution. 



Preparation. — To 900 c.c. distilled water add 18 c.c. strong 

 sulphuric acid, and add picric acid crystals to concentration. 

 Use. — Hardening reagent. 



ACETIC ACID, glacial and 1 per cent, solution. 



Preparation. — Dissolve 10 c.c. glacial acetic acid in water : 



make up to 1 litre with water. 

 Use-i — (1) For clearing tissues, and especially for rendering 



nuclei more distinct. ' 

 (2) For kUling small animals the vapour of glacial acid 



is effective. 



FORMALDEHYDE {Formal, formalin). 



Preparation. — Dilute the 40 per cent, solution to 4 per cent. 

 Use. — For preserving animals. 



