176
5.
SECTIONING
done to flatten and expand them. Indeed there is little that can be done.
Chloroform does seem to have some effect, at least with Epon. It can be
mixed about 1:1 with xylene to slow its evaporation, and then used with
a fine brush. Trichloroethylene is said also to soften Epon, and presumably might be used similarly.
5.22. Sectioning
Many people have difficulty in mastering the art of ultrathin sectioning, yet others learn this without serious trouble. It is not so much an art
as it is a skill requiring much finesse and attention to detail. One must
adopt the attitude that one is going to do the utterly impossible in cutting
sections only a few millimicrons thick. Yet the beginner must be buoyed
up by the knowledge that thousands of excellent electron micrographs
have demonstrated that it can be done. It cannot be done, however, by
working as one does in conventional microtomy. It is almost a disadvantage for the novice to know conventional methods for he has bad
habits which must be eliminated, as well as an attitude of mind about the
work that absolutely must be changed.
The unaided human eye is not enough for ultrathin sectioning. From
the time the knife is mounted in the microtome until after the sections
are finally mounted on support grids all operations must be performed
using a binocular "dissecting" microscope. The person without experience
using this instrument may have some difficulty at first with his manipulations, but he should rest assured that with practice he will learn where
his fingers are.
As a preliminary to sectioning, the microtome is cycled and stopped
so that the block is in approximately the same horizontal plane as the
knife edge. The knife is brought fairly close to the block face so that both
are visible in the same field of the binocular viewing microscope. The
binocular microscope is adjusted so that the point where the block and
knife edge will intersect is a bit above the center of the field, and is in
focus. Thus, there will be a good view of the most forward part of the
trough.
At this stage of the game, the knife will probably need a lateral
adjustment so that sections will be cut from the portion of the edge that
one desires. Since the first cuts are apt to be thick sections to face the
block, a waste portion of the knife may be used, far to one side or the
5.
SECTIONING
done to flatten and expand them. Indeed there is little that can be done.
Chloroform does seem to have some effect, at least with Epon. It can be
mixed about 1:1 with xylene to slow its evaporation, and then used with
a fine brush. Trichloroethylene is said also to soften Epon, and presumably might be used similarly.
5.22. Sectioning
Many people have difficulty in mastering the art of ultrathin sectioning, yet others learn this without serious trouble. It is not so much an art
as it is a skill requiring much finesse and attention to detail. One must
adopt the attitude that one is going to do the utterly impossible in cutting
sections only a few millimicrons thick. Yet the beginner must be buoyed
up by the knowledge that thousands of excellent electron micrographs
have demonstrated that it can be done. It cannot be done, however, by
working as one does in conventional microtomy. It is almost a disadvantage for the novice to know conventional methods for he has bad
habits which must be eliminated, as well as an attitude of mind about the
work that absolutely must be changed.
The unaided human eye is not enough for ultrathin sectioning. From
the time the knife is mounted in the microtome until after the sections
are finally mounted on support grids all operations must be performed
using a binocular "dissecting" microscope. The person without experience
using this instrument may have some difficulty at first with his manipulations, but he should rest assured that with practice he will learn where
his fingers are.
As a preliminary to sectioning, the microtome is cycled and stopped
so that the block is in approximately the same horizontal plane as the
knife edge. The knife is brought fairly close to the block face so that both
are visible in the same field of the binocular viewing microscope. The
binocular microscope is adjusted so that the point where the block and
knife edge will intersect is a bit above the center of the field, and is in
focus. Thus, there will be a good view of the most forward part of the
trough.
At this stage of the game, the knife will probably need a lateral
adjustment so that sections will be cut from the portion of the edge that
one desires. Since the first cuts are apt to be thick sections to face the
block, a waste portion of the knife may be used, far to one side or the