Reagents 27 



g) Hermann's Fluid. - 



1 per cent platinic chloride 15 parts 



Glacial acetic acid 1 part 



2 per cent osmic acid 4 or 2 parts 



This is the most expensive fixing agent yet discovered, and for 

 botanical purposes it does not seem to be any better than the cheaper 

 chromic mixtures. It is mentioned here with chromic mixtures 

 because it originated as a variation of Flemming's fluid, the platinic 

 chloride being substituted for the chromic acid. 



PICRIC ACID 



Use a saturated solution in water or 70 per cent alcohol. One 

 gram of picric acid crystals will saturate about 75 c.c. of water or 

 alcohol. This reagent penetrates well and does not make the material 

 brittle. It is to be recommended when difficulty is anticipated in 

 the cutting. If used cold, the time varies from 1 to 24 hours, de- 

 pending upon the character of the tissue and size of the specimen. 

 If used hot (85 C.), 5 or 10 minutes will be sufficient. Material 

 should be washed in 70 or 50 per cent alcohol. Water is injurious, 

 and some even go so far as to avoid aqueous stains, unless the ma- 

 terial has been thoroughly washed. The washing should be continued 

 until the material appears whitish and the alcohol no longer becomes 

 tinged with yellow. Picro-carmine gives its best result after this re- 

 agent. Picric acid can be combined with various other fixing agents, 

 and so we have picro-sulphuric acid, picro-nitric acid, picro-chromic 

 acid, picro-chromic-sulphuric acid, picro-osmic acid, picro-alcohol, 

 and picro-corrosive sublimate. The picric acid in all mixtures 

 should be rather strong. 



A picric-acid combination which has gained some popularity 

 for cytological work is 



Bouin's Fluid.- 



Formalin (commercial) 25 c.c. 



Picric acid (saturated solution in water) 75 c.c. 



Glacial acetic acid 5 c.c. 



Fix about 24 hours. Rinse in water for a few minutes to remove 

 the more superficial picric acid, and then complete the washing in 



