138
5.
SECTIONING
and the hope that more automatic, more reliable, and more
flexible
machines could achieve significant improvements in microtomy beyond
simple convenience. To a degree this has been realized, although not to
the extent that the original Porter-Blum microtome need be considered
obsolete.
The reader interested in further information about the early development of microtomes and microtomy should consult the excellent review
of Gettner and Ornstein (1956). Sitte (1955) includes a particularly complete bibliography.
In the sections which immediately follow, different microtomes that are
presently available commercially will be discussed. With one addition,
these are the instruments advertised or exhibited at the Fifth International Congress of Electron Microscopy.
5.2. The Original Porter-Blum Microtome
At the time of this writing the Porter-Blum microtome, manufactured
by Ivan Sorvall Inc., Norwalk, Connecticut, has seen more than a decade
of widespread use in laboratories throughout the world. Its behavior is
well understood. It is mechanically simple, and has proved to be a
remarkably reliable instrument. It has advantages over any of the newer
ultramicrotomes, although of course it also has some disadvantages. In
our own laboratory today, we use somewhat modified versions of this
microtome for most of our routine work simply because it is the easiest
and fastest microtome to set up and operate. This is in spite of the fact
that we have automatic microtomes available as well.
The Porter-Blum microtome has a mechanical advance mechanism of
extreme simplicity. With two exceptions, all of the other microtomes
which are presently on the market rely upon thermal expansion to advance the block. The latter sounds good in theory, but complicates
practice, for it limits operational flexibility in ways that will become
apparent later. If it were not possible to make a good mechanical drive,
one might be willing to fall back upon thermal expansion as a necessary
alternative. However, the proven reliability of the Porter-Blum microtome demonstrates that a mechanical system of screw-thread, lever-arm
and suitably designed bearings is possible and practical. One can cycle
such a system at any speed, and stop and start at will, without directly
5.
SECTIONING
and the hope that more automatic, more reliable, and more
flexible
machines could achieve significant improvements in microtomy beyond
simple convenience. To a degree this has been realized, although not to
the extent that the original Porter-Blum microtome need be considered
obsolete.
The reader interested in further information about the early development of microtomes and microtomy should consult the excellent review
of Gettner and Ornstein (1956). Sitte (1955) includes a particularly complete bibliography.
In the sections which immediately follow, different microtomes that are
presently available commercially will be discussed. With one addition,
these are the instruments advertised or exhibited at the Fifth International Congress of Electron Microscopy.
5.2. The Original Porter-Blum Microtome
At the time of this writing the Porter-Blum microtome, manufactured
by Ivan Sorvall Inc., Norwalk, Connecticut, has seen more than a decade
of widespread use in laboratories throughout the world. Its behavior is
well understood. It is mechanically simple, and has proved to be a
remarkably reliable instrument. It has advantages over any of the newer
ultramicrotomes, although of course it also has some disadvantages. In
our own laboratory today, we use somewhat modified versions of this
microtome for most of our routine work simply because it is the easiest
and fastest microtome to set up and operate. This is in spite of the fact
that we have automatic microtomes available as well.
The Porter-Blum microtome has a mechanical advance mechanism of
extreme simplicity. With two exceptions, all of the other microtomes
which are presently on the market rely upon thermal expansion to advance the block. The latter sounds good in theory, but complicates
practice, for it limits operational flexibility in ways that will become
apparent later. If it were not possible to make a good mechanical drive,
one might be willing to fall back upon thermal expansion as a necessary
alternative. However, the proven reliability of the Porter-Blum microtome demonstrates that a mechanical system of screw-thread, lever-arm
and suitably designed bearings is possible and practical. One can cycle
such a system at any speed, and stop and start at will, without directly