LIST OF REAGENTS. 491 



PERENYI'S FLUID. 



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. 



Use. Hardening reagent, especially useful for embryos. 

 Tissues after remaining in the fluid 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. Wash out in alcohol 



ACETIC ACID, glacial or 1 per cent, solution. 



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

 make up to 1 litre with water. 



Use. (1) For clearing tissues, and especially for rendering 

 nuclei more distinct. 



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

 is effective, 



FORMALDEHYDE (Formol, formalin). 



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



Use. For preserving animals, especially for hydroids, frog's 

 spawn, and gelatinous tissues such as snails. A mixture 

 of equal parts of 1 per cent, potassium bichromate and 

 8 per cent, formalin is a good hardening reagent for brain's. 

 Leave them in the mixture 2-3 weeks, then wash for 

 a day in running water, and keep in 5 per cent, formalin 

 till required. 



