5.26.
PICKING UP SECTIONS
189
become irrevocably lost. In our experience plastic containers are best for
there is only a mild tendency for sections to adhere to this material, and
their hydrophobic walls allow convex menisci to be maintained.
Also, in this respect, a hydrophobic plastic container is much superior
to a hydrophilic glass one in that it can be filled with aqueous fluids to
its brim, or even with a convex meniscus, without the fluid running over
the lip. This level can be maintained easily, and there will not be
opportunity for sections to dry down upon the sidewalls as the fluid
surface retreats.
To transfer sections to the dish, first the tip of the spatula with sections
upon it is dipped into the solution. A little of the solution is taken up
from the dish with a medicine dropper, and the surface of the spatula
is flushed with this. Naturally the same amount of solution is returned
to the dish as was taken out, so that the fluid level remains constant. The
sections are not damaged by being floated down the spatula onto the
solution surface. They will quickly leave the center of the dish and
accumulate around its rim, making light contact with the rim. Sections
of course can be floated off on a glass microscope slide in a nearly similar
way.
Sections collected at the rim of a plastic dish may be examined at one's
leisure, and under good conditions of illumination. The binocular dissecting microscope used for this purpose should be tilted so that interference colors can be seen to best advantage. Small clusters of sections can
be moved about in the dish by using a toothpick that has its tip fractured
and bent so that its wet point can come up from below the sections to be
moved. In this way good sections can be grouped together and aggregated
so that an entire specimen grid can be covered well with promising
material. Sections are picked up upon grids close to the rim of the dish
essentially in the same manner described for a direct pickup from the
trough.
Marinozzi (1961) ingeniously solved the problem of preventing sections
from adhering to container walls by confining them within a floating
ring of plastic. He cut rings of mylar sheet. We have since successfully
used polyethylene as well as dental wax for this purpose. If the outside
diameter of such a ring is substantially smaller than the container, or if
the outer rim is notched, fluid can be drained and exchanged in the container without endangering the sections.
By far the cheapest mounting grids for electron microscopy are made by
punching sheets of a copper screen material (Lektromesh) which is not
PICKING UP SECTIONS
189
become irrevocably lost. In our experience plastic containers are best for
there is only a mild tendency for sections to adhere to this material, and
their hydrophobic walls allow convex menisci to be maintained.
Also, in this respect, a hydrophobic plastic container is much superior
to a hydrophilic glass one in that it can be filled with aqueous fluids to
its brim, or even with a convex meniscus, without the fluid running over
the lip. This level can be maintained easily, and there will not be
opportunity for sections to dry down upon the sidewalls as the fluid
surface retreats.
To transfer sections to the dish, first the tip of the spatula with sections
upon it is dipped into the solution. A little of the solution is taken up
from the dish with a medicine dropper, and the surface of the spatula
is flushed with this. Naturally the same amount of solution is returned
to the dish as was taken out, so that the fluid level remains constant. The
sections are not damaged by being floated down the spatula onto the
solution surface. They will quickly leave the center of the dish and
accumulate around its rim, making light contact with the rim. Sections
of course can be floated off on a glass microscope slide in a nearly similar
way.
Sections collected at the rim of a plastic dish may be examined at one's
leisure, and under good conditions of illumination. The binocular dissecting microscope used for this purpose should be tilted so that interference colors can be seen to best advantage. Small clusters of sections can
be moved about in the dish by using a toothpick that has its tip fractured
and bent so that its wet point can come up from below the sections to be
moved. In this way good sections can be grouped together and aggregated
so that an entire specimen grid can be covered well with promising
material. Sections are picked up upon grids close to the rim of the dish
essentially in the same manner described for a direct pickup from the
trough.
Marinozzi (1961) ingeniously solved the problem of preventing sections
from adhering to container walls by confining them within a floating
ring of plastic. He cut rings of mylar sheet. We have since successfully
used polyethylene as well as dental wax for this purpose. If the outside
diameter of such a ring is substantially smaller than the container, or if
the outer rim is notched, fluid can be drained and exchanged in the container without endangering the sections.
By far the cheapest mounting grids for electron microscopy are made by
punching sheets of a copper screen material (Lektromesh) which is not