REAGENTS 
29 
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 
35 per cent or 50 per cent alcohol. There is likely to be some swelling, 
but spindles of mitotic figures stain well. The formula has given 
good results with early stages in the female gametophyte of Pinus 
and would be worth a trial with the embryo sacs of angiosperms. 
CORROSIVE SUBLIMATE 
Corrosive sublimate, or bichloride of mercury, is soluble in water 
and in alcohol. About 5 g. will make a saturated solution in 100 c.c. 
of water. It is somewhat more soluble in alcohol, but for practical 
purposes 5 g. in 100 c.c. of 50 per cent alcohol may be regarded as a 
saturated solution. Corrosive sublimate used alone does not give 
as good results as when mixed with acetic acid, chloroform, or picric 
acid. Fixing is very rapid, the material being fixed almost as soon 
as it is penetrated by the fluid. Material which is at all transparent, 
like some ovules and the endosperm of gymnosperms before the 
formation of starch, becomes opaque as soon as fixed, and so the time 
needed for fixing is easily determined. From 10 minutes to one 
hour should be sufficient for onion root-tips or lily ovaries. Smaller 
or larger objects require shorter or longer periods. When used hot 
(85° C.), the fixing is much more rapid. While a few minutes’ 
fixing may be sufficient, we let the reagent reach the boiling-point, 
then remove the flame and just as soon as the bubbling ceases, put 
the material in and leave it until the liquid becomes cool. It may 
be left for hours, without any damage. 
Wash out aqueous solutions with water and alcoholic solutions 
with alcohol. In either case, the washing must be very thorough, 
since preparations from incompletely washed material are sure to be 
disfigured by crystals of corrosive sublimate. After material fixed 
in the aqueous solution has been washed in water for an hour, add 
a little of the iodine solution used in testing for starch. The liquid will 
turn brownish or amber-colored, and then clear up; add a little more, 
