28 METHODS IN PLANT HISTOLOGY 



As in all solutions containing osmic acid, mix A and B only as 

 needed for immediate use. 



g) Benda's fluid. — 



One per cent chromic acid 16 c.c. 



Two per cent osmic acid 4 c.c. 



Glacial acetic acid 2 drops 



This modification of Flemming's stronger solution has been used in 

 various investigations upon chromatin. 



h) Merkel's fluid. — 



Equal volumes of a 1.4 per cent solution of chromic acid and a 1.4 

 per cent solution of platinic chloride. This is also an expensive re- 

 agent. It is recommended for mitotic phenomena, but does not seem 

 to equal Flemming's solution. 



i) Hermann's fluid. — 



One per cent platinic chloride 15 parts 



Glacial acetic acid 1 part 



Two per cent osmic acid 4 or 2 parts 



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

 tanical 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. Recently, it has been resur- 

 rected and highly recommended for the structure of the chromosome. 

 Personally, I do not believe it is equal to Flemming's weaker solution; 

 and, even in this weaker solution, the percentage of osmic acid may be 

 too high. 



j) Chicago formula. — 



Chromic acid 1 g. 



Glacial acetic acid 2 c.c. 



One per cent osmic acid 6 to 8 c.c. 



Water 90 c.c. 



The osmic acid, of course, to be added immediately before using. 



