(1)


e


Make a saturated solution of crystallized cal-
cium chloride in 70 p.c. alcohol, and add
alum to saturation.
Make also a saturated solution of alum in 70
p.c. alcohol, and add 1 to 2 in the proportion
of 1: 8.
To the mixture of 1 and 2 add a few drops of
a saturated solution of hematoxylin in ab-
solute alcohol.
It is often the case that hematoxylin solution
prepared in this way has not the proper
purple tint; but a red tint. This is due to
acidity of the materials used. The proper
colour can be obtained by treating it with
some alkaline solution. We have found it
convenient to use for this purpose a saturated
solution of sodium bi-carbonate in 70 p.c.
spirit. (The exact amount must be deter-
mined by experiment, as it depends upon the
amount of acid present.)


The embryo should be placed for some hours


in absolute alcohol, before staining with he-


430


PRACTICAL DIRECTIONS. [APP.
matoxylin, and should be removed directly from
absolute into the hematoxylin.
The time required for staining varies with
the size of the object and the strength of the
staining fluid. Hematoxylin will not stain if
the embryo is not quite free from acid.
If the embryo is stained too dark, it should
be treated with a solution of 70 p.c. alcohol
acidulated with nitric acid (‘25 p.c. of acid)
until the excess of staining is removed; and in
all cases the hematoxylin staining is improved
by treating the embryo with acidulated 70 p.c.
alcohol.
After staining the embryo must be well
washed in 70 and placed in 90 p.c. spirit.
With borax-carmine.
Make an aqueous solution of 2 to 3 p.c.
