LIST OF EEAGENTS, ETC. 389 



30. Picric Acid. 



Use. — Hardens tissues in two or three hours to a day, ac- 

 cording to the size of the piece, and decalcifies bony struct- 

 ures. Remove the excess of picric acid by washing in 

 alcohol, and stain picric acid preparations in alcoholic 

 stains. Transfer specimens fixed in picric acid to seven- 

 ty-five per cent., and then to ninety-five per cent, alcohol. 



Preparation. — A saturated aqueous solution is made by 

 adding crystals of the acid to distilled water until no 

 more will dissolve. 



31. Picro-sulphuric Acid {^Kleinenberg's). 



Use. — Hardens and decalcifies. To harden objects place 

 them in the fiuid for three to five hours, transfer to 

 seventy per cent, alcohol for five to six hours, then place 

 in ninety per cent, alcohol, and change the latter as of- 

 ten as it becomes discolored. 



Preparation. — To one hundred volumes of a saturated so- 

 lution of picric acid in distilled water add two volumes 

 of concentrated sulphuric acid. Filter this mixture 

 and dilute it with three times its volume of distilled 

 water. 



32. Pith. 



Bunches of pith may be obtained from dealers in watch- 

 makers' supplies. 



33. Potash. 



Use. — Clears vegetable tissues by causing the cell -walls, 

 starch grains, etc., to swell, and the proteid crystalloids 

 and aleurone to dissolve. 



Preparation. — Potassium hydroxide comes in the form of 

 sticks. These usually have an opaque white coating of 

 potassium carbonate, which should be dissolved off, and 

 only the central, transparent part of the stick used. 

 Make a concentrated solution by dissolving twenty-five 

 grams of potassium hydroxide in seventy-five cubic centi- 

 metres of distilled water. Make the five per cent, (dilute) 



