Bright Instruments
39
3.2 FITTING THE SPECIMEN CONT.
e. Before the embedding compound starts
to freeze place the tissue in the correct
orientation, holding it with a pair of forceps.
Take care that the forceps do not freeze to
your tissue. If your tissue is fresh you will see
the freezing isotherm gradually rise through
the tissue, as a white line.
f. Remove the object holder from the
quick freezer and place it in the V block or
cryomatic block and tighten the screw firmly
to hold it in position. Wait a few minutes for
temperatures to equalise before trimming.
It is often best to set up a new blade, knife
or anti-roll plate using some embedding
compound first. Proceed as follows:
a. Follow steps 1 to 4 above.
b. Watch the embedding compound and
suddenly it will be seen to freeze as it turns
from transparent to a dense white colour.
Watch the freezing isotherm until just before
it reaches the top surface of the embedding
compound and while it is still liquid, carefully
apply some more embedding compound
until it forms a mound on the top. Then let it
continue to freeze until it is completely solid.
c. Remove the object holder from the quick
freezer and place it in the microtome.
NOTE 1:
If you are unlucky enough to have
your object holder freeze solidly into ice on
the quick freezer plate, a little 90% ethanol
solution around the base or neck of the
chuck will act as an antifreeze to release
it. Be careful if you do this because the
ethanol will also lower the melting point of
your specimen.
NOTE 2:
If you are using pre-frozen
tissue then it will be much colder than
its optimum cutting temperature and
therefore plenty of time must be allowed
for temperature to equalise in the specimen
before cutting.
NOTE 3:
It is important that after use the
frost elimination cover should be replaced
on the quick freezer plate.
3. Cutting & Collecting
Sections Cont.
