188
5.
SECTIONING
sections from below. Sections are apt to be hard to center, though, if they
are stuck to the knife or trough wall.
It is also possible to pick up sections with a small loop of thin platinum
or other wire. The diameter of the loop should not greatly exceed ^ in.,
but this is adequate so that a fluid film with sections can be lowered over
a supporting grid that is mounted on a small peg. Thus, sections can be
transferred to a grid surface in this manner. Also sections can be placed
on glass slides in this way for conventional microscopy. For the latter
purpose it allows a fairly exact positioning of the sections that otherwise
is difficult.
For some purposes it is desirable to transfer sections from the trough
to a dish, or even to a glass slide if they are to be examined by conventional microscopy. For instance, floating sections might be transferred to
a container with stain before mounting them on grids. There is a simple
and almost foolproof way of removing sections from the trough and
making such a transfer providing that the trough fluid is a dilute acetone
solution which has a lower surface tension than pure water. The method
takes advantage of a surface tension gradient that then can be established
without difficulty. The only equipment used is a "glass spatula." This is
made by diagonally breaking an ordinary 1x3 in. microscope slide so
that it has a blunt end, a little narrower than the trough (Fig. 18). This is
kept thoroughly wet in a small beaker of water. The wet tip of the
spatula is introduced into the trough reasonably close to the floating
sections. The greater surface tension of the water film upon the spatula
causes the sections to glide up upon this. Gentle nudging may be needed
to free ribbons attached to the knife edge or to the side walls of the
trough. The whole operation takes much less time to accomplish than to
describe. This procedure also serves very well to clean the surface of the
trough fluid which is an additional advantage.
Since this method of picking up sections depends upon a surface tension
gradient, it is obvious that it will be most effective when the gradient is
steep. Thus, the stronger the acetone solution the easier it is to achieve
success. It must also be understood that the spatula must be truly wet by
the water. It is prone to become hydrophobic with use, but it can be made
hydrophilic by dipping it in alcohol, wiping it vigorously, and then
returning it to its water bath.
Containers to which sections might be transferred should not ordinarily
be of glass. Sections then are apt to climb up the sidewalls on the curving
concave menisci, and they will stick to dry glass with great tenacity and
5.
SECTIONING
sections from below. Sections are apt to be hard to center, though, if they
are stuck to the knife or trough wall.
It is also possible to pick up sections with a small loop of thin platinum
or other wire. The diameter of the loop should not greatly exceed ^ in.,
but this is adequate so that a fluid film with sections can be lowered over
a supporting grid that is mounted on a small peg. Thus, sections can be
transferred to a grid surface in this manner. Also sections can be placed
on glass slides in this way for conventional microscopy. For the latter
purpose it allows a fairly exact positioning of the sections that otherwise
is difficult.
For some purposes it is desirable to transfer sections from the trough
to a dish, or even to a glass slide if they are to be examined by conventional microscopy. For instance, floating sections might be transferred to
a container with stain before mounting them on grids. There is a simple
and almost foolproof way of removing sections from the trough and
making such a transfer providing that the trough fluid is a dilute acetone
solution which has a lower surface tension than pure water. The method
takes advantage of a surface tension gradient that then can be established
without difficulty. The only equipment used is a "glass spatula." This is
made by diagonally breaking an ordinary 1x3 in. microscope slide so
that it has a blunt end, a little narrower than the trough (Fig. 18). This is
kept thoroughly wet in a small beaker of water. The wet tip of the
spatula is introduced into the trough reasonably close to the floating
sections. The greater surface tension of the water film upon the spatula
causes the sections to glide up upon this. Gentle nudging may be needed
to free ribbons attached to the knife edge or to the side walls of the
trough. The whole operation takes much less time to accomplish than to
describe. This procedure also serves very well to clean the surface of the
trough fluid which is an additional advantage.
Since this method of picking up sections depends upon a surface tension
gradient, it is obvious that it will be most effective when the gradient is
steep. Thus, the stronger the acetone solution the easier it is to achieve
success. It must also be understood that the spatula must be truly wet by
the water. It is prone to become hydrophobic with use, but it can be made
hydrophilic by dipping it in alcohol, wiping it vigorously, and then
returning it to its water bath.
Containers to which sections might be transferred should not ordinarily
be of glass. Sections then are apt to climb up the sidewalls on the curving
concave menisci, and they will stick to dry glass with great tenacity and