5.11.
CLEVENGER'S (1963) MICROTOME
147
This microtome employs a mechanical advance mechanism working
through a lever system. The mechanical advantage of the levers can be
varied, however, from zero to a large value so that the mechanical advance
is completely flexible and variable. It is possible to change the advance
over a wide range, but not the full range, while the instrument is
operating.
The cutting speed is completely variable through the most pertinent
range, from 2.4-0.09 mm/sec. While surely this spans the range of interest
for most biological work employing standard embedments, the microtome
would not serve for those special problems in industrial microscopy
which occasionally seem to require high cutting speeds (metals, rubbers,
etc.).
This microtome completes most of each cycle relatively rapidly, and
then is slowed automatically for the cutting stroke. A cam controls this
so that there is a fixed proportionality between the cutting speed and the
cycle length. With particularly slow sectioning the cycles become inordinately long. However, the system is a great improvement over a
simple direct drive.
The knife carriage can be pivoted through a 90° arc so that it can be
used with an old knife for the precise trimming of specimen blocks. In
other respects the knife carriage also is well designed. Although the
microtome can be operated by a hand crank, it is not likely that this will
be used widely except for trimming purposes, or for cutting thick sections.
In spite of the considerable mechanical complexity of this instrument
it should not present serious servicing problems. The parts immediately
concerned with moving the specimen block are simple and are fairly well
isolated from controlling mechanisms. Normally the microtome will be
sold with a built-in binocular microscope, and it has an adequate illuminator. This should prove to be an excellent instrument for serial sectioning. It is not unduly sensitive to external vibrations or thermal fluctuations.
5.11. Clevenger's (1963) Microtome
It is a false notion that very expensive microtomes are truly necessary
for the ultrathin sectioning that electron microscopy requires. Several of
the earliest designs were simple in the extreme, yet were effective. Indeed,
the original Porter-Blum (1953) prototype instrument fell into this
CLEVENGER'S (1963) MICROTOME
147
This microtome employs a mechanical advance mechanism working
through a lever system. The mechanical advantage of the levers can be
varied, however, from zero to a large value so that the mechanical advance
is completely flexible and variable. It is possible to change the advance
over a wide range, but not the full range, while the instrument is
operating.
The cutting speed is completely variable through the most pertinent
range, from 2.4-0.09 mm/sec. While surely this spans the range of interest
for most biological work employing standard embedments, the microtome
would not serve for those special problems in industrial microscopy
which occasionally seem to require high cutting speeds (metals, rubbers,
etc.).
This microtome completes most of each cycle relatively rapidly, and
then is slowed automatically for the cutting stroke. A cam controls this
so that there is a fixed proportionality between the cutting speed and the
cycle length. With particularly slow sectioning the cycles become inordinately long. However, the system is a great improvement over a
simple direct drive.
The knife carriage can be pivoted through a 90° arc so that it can be
used with an old knife for the precise trimming of specimen blocks. In
other respects the knife carriage also is well designed. Although the
microtome can be operated by a hand crank, it is not likely that this will
be used widely except for trimming purposes, or for cutting thick sections.
In spite of the considerable mechanical complexity of this instrument
it should not present serious servicing problems. The parts immediately
concerned with moving the specimen block are simple and are fairly well
isolated from controlling mechanisms. Normally the microtome will be
sold with a built-in binocular microscope, and it has an adequate illuminator. This should prove to be an excellent instrument for serial sectioning. It is not unduly sensitive to external vibrations or thermal fluctuations.
5.11. Clevenger's (1963) Microtome
It is a false notion that very expensive microtomes are truly necessary
for the ultrathin sectioning that electron microscopy requires. Several of
the earliest designs were simple in the extreme, yet were effective. Indeed,
the original Porter-Blum (1953) prototype instrument fell into this