5.21.
FLATTENING SECTIONS
175
In starting one's sectioning it is desirable to have the meniscus low
rather than high. The block then can be faced without being wet and the
edge contaminated, and a ribbon of sorts can be started. It is then easy to
add a drop or two of acetone solution and get successive sections which
glide smoothly, away from the edge.
Occasionally, as one attempts to section, the block seems particularly
prone to being wet. Sometimes such blocks can be successfully started by
lowering the meniscus to the point where there is incipient drying of the
edge. Then a few rumpled sections may be cut which are at least dry.
More acetone is then added judiciously to raise the meniscus a bit until
smooth expanded sections follow. These difficulties occur mainly when
the knife is broken in such a way that the actual edge angle is decidedly
obtuse, and therefore requires a relatively high meniscus.
There is some reason to believe that static electricity at times augments
tendencies to wet, and this can be eliminated by exposing the block and
knife area to low energy ionizing radiation. A Staticmaster polonium
strip, mounted on a flexible arm, serves this purpose well.
Acetone is a possible source of several contaminants and only reagent
grade acetone should be used, diluted with demineralized or distilled
water. Otherwise various oily films may appear which not only are likely
to contaminate the knife edge, but may leave very messy deposits on the
sections so that they become almost too dirty to be used finally. Also,
some tap waters may precipitate mineral salts which will dirty the sections.
5.21. Flattening Sections
Methacrylate sections, in particular, are not necessarily fully expanded
by the trough fluid. Morgan et al. (1956) noted that sections may remain
compressed to some degree so that structures which should have circular
profiles are found to be elliptical, with short axes parallel to the direction
of sectioning. To a large extent this can be eliminated by softening the
methacrylate somewhat with the vapor fumes of a volatile solvent, whereupon surface tension will produce fuller expansion. Thus, a fine camel's
hair brush or a wisp of cotton on a toothpick dampened with xylene or
toluene can be brought judiciously near sections as they float in the
trough upon the acetone (Satir and Peachey, 1958).
When epoxy or polyester sections are cut there is little that need be
FLATTENING SECTIONS
175
In starting one's sectioning it is desirable to have the meniscus low
rather than high. The block then can be faced without being wet and the
edge contaminated, and a ribbon of sorts can be started. It is then easy to
add a drop or two of acetone solution and get successive sections which
glide smoothly, away from the edge.
Occasionally, as one attempts to section, the block seems particularly
prone to being wet. Sometimes such blocks can be successfully started by
lowering the meniscus to the point where there is incipient drying of the
edge. Then a few rumpled sections may be cut which are at least dry.
More acetone is then added judiciously to raise the meniscus a bit until
smooth expanded sections follow. These difficulties occur mainly when
the knife is broken in such a way that the actual edge angle is decidedly
obtuse, and therefore requires a relatively high meniscus.
There is some reason to believe that static electricity at times augments
tendencies to wet, and this can be eliminated by exposing the block and
knife area to low energy ionizing radiation. A Staticmaster polonium
strip, mounted on a flexible arm, serves this purpose well.
Acetone is a possible source of several contaminants and only reagent
grade acetone should be used, diluted with demineralized or distilled
water. Otherwise various oily films may appear which not only are likely
to contaminate the knife edge, but may leave very messy deposits on the
sections so that they become almost too dirty to be used finally. Also,
some tap waters may precipitate mineral salts which will dirty the sections.
5.21. Flattening Sections
Methacrylate sections, in particular, are not necessarily fully expanded
by the trough fluid. Morgan et al. (1956) noted that sections may remain
compressed to some degree so that structures which should have circular
profiles are found to be elliptical, with short axes parallel to the direction
of sectioning. To a large extent this can be eliminated by softening the
methacrylate somewhat with the vapor fumes of a volatile solvent, whereupon surface tension will produce fuller expansion. Thus, a fine camel's
hair brush or a wisp of cotton on a toothpick dampened with xylene or
toluene can be brought judiciously near sections as they float in the
trough upon the acetone (Satir and Peachey, 1958).
When epoxy or polyester sections are cut there is little that need be