4.19.
PREPARING THE BLOCK FOR SECTIONING
131
in this regard. A commercial drill-chuck can be purchased separately
and used as a hand vice for this purpose. Reimann (1963) has described
a clamp made simply by boring a hole of appropriate size between two
aluminum bars such that the capsule is gripped securely when the bars
are screwed together. The specimen area, then, can be illuminated from
below while it is being trimmed. Danon (1961) has described a fairly
elaborate jig for holding and trimming capsules at predetermined angles.
Certain of the newer microtomes such as the LKB "Ultratome" and the
Sorvall M-2 instruments have such latitude in their knife holders that
these instruments can be used as trimming devices as well as playing
their more important roles [see Galey (1963) for a manipulative technique based on the former instrument].
The face which is to be sectioned should be trimmed actually into
the tissue mass. Nothing is more frustrating than to prepare sections and
discover when they reach the microscope that they are of empty plastic.
In trimming freehand under a binocular dissecting microscope one
ordinarily can see osmium-fixed material in the relatively thick sections
that are cut in facing the block. If there is doubt about whether tissue
has been reached, the freehand sections can be transferred to a glass
slide, then covered with a drop of immersion oil, and examined with a
compound microscope using the condenser diaphragm nearly closed.
Enough contrast usually can be obtained to see embedded tissue even
though it is not stained. Better yet, one can use phase microscopy (Chapter 7.12). In trimming and facing a block it is often desirable to be
able to recognize under low magnification a structure that it may contain. Gray (1961) points out that if a piece of very thin cigarette paper
is inserted under a reasonably thin surface flap that has been cut freehand, reflected light may show enough tissue detail to make an exact
orientation possible.
It is permissible, indeed desirable, to trim the side and end walls of
the block into the tissue mass itself. Unlike in conventional microscopy
there is no advantage in having empty embedment surrounding the
tissue in a section. All that a rim of blank plastic does is to increase the
hazards of sectioning by making the sections unnecessarily large, and to
cause irritation when finally examining the sections in the electron
microscope.
When it becomes important to orient a tissue specimen in some
special manner, it often becomes necessary to mount the block on some
sort of a holder. Short sections of wooden dowel rods of suitable diam-
PREPARING THE BLOCK FOR SECTIONING
131
in this regard. A commercial drill-chuck can be purchased separately
and used as a hand vice for this purpose. Reimann (1963) has described
a clamp made simply by boring a hole of appropriate size between two
aluminum bars such that the capsule is gripped securely when the bars
are screwed together. The specimen area, then, can be illuminated from
below while it is being trimmed. Danon (1961) has described a fairly
elaborate jig for holding and trimming capsules at predetermined angles.
Certain of the newer microtomes such as the LKB "Ultratome" and the
Sorvall M-2 instruments have such latitude in their knife holders that
these instruments can be used as trimming devices as well as playing
their more important roles [see Galey (1963) for a manipulative technique based on the former instrument].
The face which is to be sectioned should be trimmed actually into
the tissue mass. Nothing is more frustrating than to prepare sections and
discover when they reach the microscope that they are of empty plastic.
In trimming freehand under a binocular dissecting microscope one
ordinarily can see osmium-fixed material in the relatively thick sections
that are cut in facing the block. If there is doubt about whether tissue
has been reached, the freehand sections can be transferred to a glass
slide, then covered with a drop of immersion oil, and examined with a
compound microscope using the condenser diaphragm nearly closed.
Enough contrast usually can be obtained to see embedded tissue even
though it is not stained. Better yet, one can use phase microscopy (Chapter 7.12). In trimming and facing a block it is often desirable to be
able to recognize under low magnification a structure that it may contain. Gray (1961) points out that if a piece of very thin cigarette paper
is inserted under a reasonably thin surface flap that has been cut freehand, reflected light may show enough tissue detail to make an exact
orientation possible.
It is permissible, indeed desirable, to trim the side and end walls of
the block into the tissue mass itself. Unlike in conventional microscopy
there is no advantage in having empty embedment surrounding the
tissue in a section. All that a rim of blank plastic does is to increase the
hazards of sectioning by making the sections unnecessarily large, and to
cause irritation when finally examining the sections in the electron
microscope.
When it becomes important to orient a tissue specimen in some
special manner, it often becomes necessary to mount the block on some
sort of a holder. Short sections of wooden dowel rods of suitable diam-