5.26.
PICKING UP SECTIONS
187
(7) A light touch. The microtome can be deformed enough to ruin
quality sectioning simply by a firm grasp on the microtome handle.
(8) Meniscus. Too low a meniscus is apt to be the common fault. Back
pressures may be created which will prevent the sections from flattening
out on the fluid surface as they should. Too high a meniscus is apt to wet
the block face which in turn will carry fluid to the knife face, which may
result in contamination.
(9) Vibrations. The microtome table should be steady. The operator
should not touch the table with hands, elbows, or feet while sectioning.
5.26.
Picking Up Sections
Before sections can be examined in the electron microscope they must
be mounted on suitable specimen grids and perhaps given additional
support with a backing film of one sort or another. The various ways
that sections can be supported are discussed in detail in the next chapter.
Here we are concerned with getting the sections to the grid which may
already have a supporting film upon it.
The simplest way to pick up sections is the best way except, perhaps,
for methacrylate sections. One need only take a screen in fine tipped forceps and bend its edge slightly so that it can be laid flat upon the surface
of the fluid in the trough. It is simply laid across a ribbon or raft of
sections, and then pulled away, or it may be pushed on down into the
trough fluid, then turned over and finally removed. Sections stick
vigorously to a dry screen or to a screen which has been coated with a
supporting film. No further attachment is necessary other than simple
contact. However, the screen must not be wet before contact so that it
must not be tilted as one comes down over the sections, and this motion
should not be made too slowly or condensation of water may occur.
The disadvantages of this simple method of picking up sections include:
(1) the very real danger of damaging the knife edge, either by direct
contact or by contamination; (2) the difficulty of orienting the sections
very well on the screen, or assembling a group of sections in one place
so that they are put on a single screen; (3) the probability that any contaminants on the surface of the trough fluid will be scattered over the
sections, thus dirtying them to the point where their usefulness is seriously
impaired.
A variant of this method is to dip the screen first, and approach the
PICKING UP SECTIONS
187
(7) A light touch. The microtome can be deformed enough to ruin
quality sectioning simply by a firm grasp on the microtome handle.
(8) Meniscus. Too low a meniscus is apt to be the common fault. Back
pressures may be created which will prevent the sections from flattening
out on the fluid surface as they should. Too high a meniscus is apt to wet
the block face which in turn will carry fluid to the knife face, which may
result in contamination.
(9) Vibrations. The microtome table should be steady. The operator
should not touch the table with hands, elbows, or feet while sectioning.
5.26.
Picking Up Sections
Before sections can be examined in the electron microscope they must
be mounted on suitable specimen grids and perhaps given additional
support with a backing film of one sort or another. The various ways
that sections can be supported are discussed in detail in the next chapter.
Here we are concerned with getting the sections to the grid which may
already have a supporting film upon it.
The simplest way to pick up sections is the best way except, perhaps,
for methacrylate sections. One need only take a screen in fine tipped forceps and bend its edge slightly so that it can be laid flat upon the surface
of the fluid in the trough. It is simply laid across a ribbon or raft of
sections, and then pulled away, or it may be pushed on down into the
trough fluid, then turned over and finally removed. Sections stick
vigorously to a dry screen or to a screen which has been coated with a
supporting film. No further attachment is necessary other than simple
contact. However, the screen must not be wet before contact so that it
must not be tilted as one comes down over the sections, and this motion
should not be made too slowly or condensation of water may occur.
The disadvantages of this simple method of picking up sections include:
(1) the very real danger of damaging the knife edge, either by direct
contact or by contamination; (2) the difficulty of orienting the sections
very well on the screen, or assembling a group of sections in one place
so that they are put on a single screen; (3) the probability that any contaminants on the surface of the trough fluid will be scattered over the
sections, thus dirtying them to the point where their usefulness is seriously
impaired.
A variant of this method is to dip the screen first, and approach the