5.16.
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163
knife introduces somewhat different problems than when cutting with
glass. In particular, the trough fluid should have a higher surface tension
with the diamond knives than with glass. Thus, pure water usually is
preferable to a dilute acetone solution. Minute amounts of protein
(crystalline albumen, or even traces of saliva), which help wet the
diamond, also sometimes seem desirable. Although most embedments can
be sectioned well either with a glass knife or a diamond knife, there are
special situations where one or the other cannot be used as effectively.
Recently, in sectioning material embedded in hydroxypropyl methacrylate, we had no particular difficulty with glass knives, but invariably
produced closely spaced folds when a diamond knife was used, which we
attributed to an unusually strong adhesive force between this plastic and
the diamond edge. Conversely, some Epon blocks apparently can be cut
smoothly only with diamond knives (Chapter 4.11, Fig. 11).
Diamond knives are also particularly advantageous for certain types of
"difficult" tissues. These are mainly dense connective tissues containing
heavy collagenous fibers. Then it is desirable to have harder blocks than
customary, and to trim them more ruthlessly than usual. During the last
year, numerous attempts to section human elastic cartilage with glass
knives proved to be most discouraging, but there was not great difficulty
with a good diamond knife.
Diamond knife edges are cleaned by rubbing them with a thin sliver of
soft wood, wet with acetone or other organic solvent. The sliver is prepared by making long intersecting diagonal cuts through an applicator
stick, a match, or a toothpick. A flat side of the thin wedge then is drawn
gently along the edge of the knife so that it may actually be cut slightly
by the knife. This should be done while being observed with a microscope. An even more gentle treatment which is effective is to use a thin
strip of balsa wood for this purpose, or a sliver of cork glued to a stick as
a holder. Originally, it was thought that strong acids could be used for
cleaning diamond knives, but there is some reason to believe that
deterioration may result from such treatments.
One serious drawback to diamond knives is their fragility. The edge,
being thin, is reasonably flexible, but it can be chipped through carelessness. It is most important to avoid rubbing it in a transverse direction.
I am sure that many a knife has been utterly ruined by jamming it into
a block or chuck when positioning the knife holder, or by touching it
with a pair of forceps or a needle while working in the trough area.
Considering that diamond knives are worth several hundred dollars, a
DIAMOND KNIVES
163
knife introduces somewhat different problems than when cutting with
glass. In particular, the trough fluid should have a higher surface tension
with the diamond knives than with glass. Thus, pure water usually is
preferable to a dilute acetone solution. Minute amounts of protein
(crystalline albumen, or even traces of saliva), which help wet the
diamond, also sometimes seem desirable. Although most embedments can
be sectioned well either with a glass knife or a diamond knife, there are
special situations where one or the other cannot be used as effectively.
Recently, in sectioning material embedded in hydroxypropyl methacrylate, we had no particular difficulty with glass knives, but invariably
produced closely spaced folds when a diamond knife was used, which we
attributed to an unusually strong adhesive force between this plastic and
the diamond edge. Conversely, some Epon blocks apparently can be cut
smoothly only with diamond knives (Chapter 4.11, Fig. 11).
Diamond knives are also particularly advantageous for certain types of
"difficult" tissues. These are mainly dense connective tissues containing
heavy collagenous fibers. Then it is desirable to have harder blocks than
customary, and to trim them more ruthlessly than usual. During the last
year, numerous attempts to section human elastic cartilage with glass
knives proved to be most discouraging, but there was not great difficulty
with a good diamond knife.
Diamond knife edges are cleaned by rubbing them with a thin sliver of
soft wood, wet with acetone or other organic solvent. The sliver is prepared by making long intersecting diagonal cuts through an applicator
stick, a match, or a toothpick. A flat side of the thin wedge then is drawn
gently along the edge of the knife so that it may actually be cut slightly
by the knife. This should be done while being observed with a microscope. An even more gentle treatment which is effective is to use a thin
strip of balsa wood for this purpose, or a sliver of cork glued to a stick as
a holder. Originally, it was thought that strong acids could be used for
cleaning diamond knives, but there is some reason to believe that
deterioration may result from such treatments.
One serious drawback to diamond knives is their fragility. The edge,
being thin, is reasonably flexible, but it can be chipped through carelessness. It is most important to avoid rubbing it in a transverse direction.
I am sure that many a knife has been utterly ruined by jamming it into
a block or chuck when positioning the knife holder, or by touching it
with a pair of forceps or a needle while working in the trough area.
Considering that diamond knives are worth several hundred dollars, a