FIXING AGENTS

dou 1 tissues. If the immersion is to be a long one the tissues must
4tis  be placed with the solution in well-closed vessels, as osmium
eat i is very volatile.
Great stress is laid by authors on the fact that the vapour
ia  of osmium is very irritating to mucous tissues. It is said that
as   the slightest exposure to it is sufficient to give rise to serious
1,bI  catarrh, irritation of the bronchial tubes, laryngeal catarrh,
eR  conjunctivitis, &c.  I think these statements greatly exag-
Cent  gerated. I have frequently dissected for an hour at a time
sea   over a watch-glass containing 1 per cent. osmic acid solution
our;  and placed on the stage of the dissecting microscope, and
trM, that without experiencing any evil effects more serious than a
Ao.  disagreeable perception of the pungency and chokiness of the
:osrr  atmosphere. A good draught should of course be kept up
ol  by means of an open window or other arrangement. Stock
te to  solutions must be kept in stoppered bottles, and the bottles
To or  ought to be furnished with pipette stoppers or some con-
'n  trivance by which a small quantity of the solution can be
11  obtained when wanted without risk of portions of organic
dust falling into the bottle.
quel  13. Chromic and  Osmic Acid     Fixing   Mixture    (Max
n Flesch's formulal).-This mixture (osmium         0-10, chromic
acid 025, water 100-0), originally introduced for the prepara-
tion of the auditory organ of vertebrates, is of general appli-
cation. It does not require to be kept in the dark. Objects
Lr .  may remain in it for twenty-four to thirty-six hours without
risk of the osmic acid over-blackening them.        Flemming
is it  found it to preserve nuclear figures well; but the preparations
iro  are pale, and difficult to stain well. He finds that the action
ler's  of the mixture is improved (for nuclear figures) by the
r in  addition of acetic, formic, or other acid.    This addition
1    brings out the figures more sharply, and has the further
advantage of allowing of a sharper stain with huematoxylin,
1 ' Arch. Mik. Anat.,' xvi (1878), p. 300.

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