4.19.
PREPARING THE BLOCK FOR SECTIONING
133
eter will fit into the chuck of any microtome and serve this purpose
very well. The dowel rod can be trimmed with a hand pencil sharpener
as indicated in Fig. 13(e). The end of the dowel which is to receive the
specimen block is prepared by dipping this in a melted carnauba-paraffin
wax mixture. If the latter contains 25-33% carnauba wax, its support
will be rigid. Before use, however, carnauba wax must be filtered for all
that we have seen has contained much grit.
If the orientation of the specimen must be changed considerably from
the way it lies in the capsule, it is convenient to trim the specimen block
almost to its final form while it is still left attached to the main mass of
plastic. The latter serves as a handle making the operation easy to
complete if the necessary razor cuts are planned in advance so they can
be done in a reasonable sequence, always leaving plastic to push against.
Figures 13(a)-(f) indicate how a flat piece of tissue can be trimmed so
that finally it is mounted on edge to be cut transversely. However, very
brittle plastics cannot be precisely trimmed until mounted in their final
position.
A flat piece of tissue, of course, sinks to the bottom of the capsule,
as in Fig. 13(a), where it can only be cut in the horizontal plane if it is
not removed from the capsule and remounted. In Fig. 13(c) the truncated pyramid remains attached to the main mass of the capsule by only
a narrow neck. At this stage it is immersed briefly in the molten carnauba-paraffin mixture to allow good bonding. The neck plastic then
is cut without difficulty, and the block is oriented on the dowel rod as
indicated in Fig. 13(e). It usually is necessary to melt the wax and maneuver the specimen with a hot scalpel blade to accomplish this. This, of
course, is done with the aid of a low power binocular dissecting microscope. When the orientation is regarded as satisfactory, the tip of the
dowel including the block can be dipped in the hot wax bath to build
up the wax mass if necessary [Fig. 13(f)]. It is held in the hot wax long
The specimen should be so trimmed that nothing but facing is required of the
finished mount (f). To do this conveniently, the trimming process should be plotted
in advance, and the sequence such that as much support as possible is retained during
the cutting. Usually it is best to leave the specimen attached to the capsular mass
through the wax dip, for then one has a convenient "handle." Finally the specimen is
detached by cutting the last remaining thin neck of plastic. The geometry of the specimen and the orientation required will determine just how these operations are performed, but a flat sheet or a long cord of tissue can easily be mounted vertically in this
way irrespective of how it happened to lie in the capsule.
PREPARING THE BLOCK FOR SECTIONING
133
eter will fit into the chuck of any microtome and serve this purpose
very well. The dowel rod can be trimmed with a hand pencil sharpener
as indicated in Fig. 13(e). The end of the dowel which is to receive the
specimen block is prepared by dipping this in a melted carnauba-paraffin
wax mixture. If the latter contains 25-33% carnauba wax, its support
will be rigid. Before use, however, carnauba wax must be filtered for all
that we have seen has contained much grit.
If the orientation of the specimen must be changed considerably from
the way it lies in the capsule, it is convenient to trim the specimen block
almost to its final form while it is still left attached to the main mass of
plastic. The latter serves as a handle making the operation easy to
complete if the necessary razor cuts are planned in advance so they can
be done in a reasonable sequence, always leaving plastic to push against.
Figures 13(a)-(f) indicate how a flat piece of tissue can be trimmed so
that finally it is mounted on edge to be cut transversely. However, very
brittle plastics cannot be precisely trimmed until mounted in their final
position.
A flat piece of tissue, of course, sinks to the bottom of the capsule,
as in Fig. 13(a), where it can only be cut in the horizontal plane if it is
not removed from the capsule and remounted. In Fig. 13(c) the truncated pyramid remains attached to the main mass of the capsule by only
a narrow neck. At this stage it is immersed briefly in the molten carnauba-paraffin mixture to allow good bonding. The neck plastic then
is cut without difficulty, and the block is oriented on the dowel rod as
indicated in Fig. 13(e). It usually is necessary to melt the wax and maneuver the specimen with a hot scalpel blade to accomplish this. This, of
course, is done with the aid of a low power binocular dissecting microscope. When the orientation is regarded as satisfactory, the tip of the
dowel including the block can be dipped in the hot wax bath to build
up the wax mass if necessary [Fig. 13(f)]. It is held in the hot wax long
The specimen should be so trimmed that nothing but facing is required of the
finished mount (f). To do this conveniently, the trimming process should be plotted
in advance, and the sequence such that as much support as possible is retained during
the cutting. Usually it is best to leave the specimen attached to the capsular mass
through the wax dip, for then one has a convenient "handle." Finally the specimen is
detached by cutting the last remaining thin neck of plastic. The geometry of the specimen and the orientation required will determine just how these operations are performed, but a flat sheet or a long cord of tissue can easily be mounted vertically in this
way irrespective of how it happened to lie in the capsule.