144
5.
SECTIONING
arm is directly connected to the base, and its movement depends upon the
arm's intrinsic flexibility. The free end of the specimen rod is guided
along a compound curve by a two lever system to cycle the instrument.
Bearings are involved in this control mechanism.
The automatic feed is not continuous, but rather in increments of
250 A. The minimum cutting speed is 5 mm/sec. Its cycling time at this
speed is 10 seconds. The present instrument seems to have a particularly
well-designed knife carrier. A binocular microscope and a
fluorescent
light source are built into the microtome as an integral part of it.
I have not had personal experience with this microtome, but I am
aware of its being used successfully in some European laboratories.
5.7. Cambridge Ultramicrotome
This microtome was developed by A. F. Huxley, and the commercial
version is made and marketed by the Cambridge Instrument Co., Ltd.,
London, S. W. 1. It has a mechanical drive which includes a rather long
system of lever arms. One might think this would make the instrument
unduly sensitive to thermal
fluctuations,
but apparently this is not a
serious problem if precaution is taken to avoid severe drafts. Leaf-springs
allow movements in single planes.
In one sense the instrument is not fully automatic for one lifts a lever
to initiate cutting. This triggers a mechanism, however, which then
allows the specimen arm to drop under the influence of gravity. The
rate of the fall is controlled by an oil-filled dashpot. The piston in the
dashpot incorporates a valve which can be adjusted to allow oil to pass
from one side of the piston to the other at a controlled rate, and so the
piston sinks at a speed proportionate to the size of the leak deliberately
created. This mechanism allows the specimen arm to fall in a particularly
constant and vibrationless manner. Also the rate of descent can be
reduced at will to very low values. Thus, the microtome has greater
flexibility
than any other instrument on the market insofar as slow cutting
speeds are concerned. After the cutting stroke is completed, the instrument can be recycled without delay. Cycling can be performed
rapidly which advantageously minimizes its length. The specimen advance
is in increments of 50 A.
The extreme flexibility of the cutting speed coupled with the short
cycling time have made this a popular microtome in many laboratories
5.
SECTIONING
arm is directly connected to the base, and its movement depends upon the
arm's intrinsic flexibility. The free end of the specimen rod is guided
along a compound curve by a two lever system to cycle the instrument.
Bearings are involved in this control mechanism.
The automatic feed is not continuous, but rather in increments of
250 A. The minimum cutting speed is 5 mm/sec. Its cycling time at this
speed is 10 seconds. The present instrument seems to have a particularly
well-designed knife carrier. A binocular microscope and a
fluorescent
light source are built into the microtome as an integral part of it.
I have not had personal experience with this microtome, but I am
aware of its being used successfully in some European laboratories.
5.7. Cambridge Ultramicrotome
This microtome was developed by A. F. Huxley, and the commercial
version is made and marketed by the Cambridge Instrument Co., Ltd.,
London, S. W. 1. It has a mechanical drive which includes a rather long
system of lever arms. One might think this would make the instrument
unduly sensitive to thermal
fluctuations,
but apparently this is not a
serious problem if precaution is taken to avoid severe drafts. Leaf-springs
allow movements in single planes.
In one sense the instrument is not fully automatic for one lifts a lever
to initiate cutting. This triggers a mechanism, however, which then
allows the specimen arm to drop under the influence of gravity. The
rate of the fall is controlled by an oil-filled dashpot. The piston in the
dashpot incorporates a valve which can be adjusted to allow oil to pass
from one side of the piston to the other at a controlled rate, and so the
piston sinks at a speed proportionate to the size of the leak deliberately
created. This mechanism allows the specimen arm to fall in a particularly
constant and vibrationless manner. Also the rate of descent can be
reduced at will to very low values. Thus, the microtome has greater
flexibility
than any other instrument on the market insofar as slow cutting
speeds are concerned. After the cutting stroke is completed, the instrument can be recycled without delay. Cycling can be performed
rapidly which advantageously minimizes its length. The specimen advance
is in increments of 50 A.
The extreme flexibility of the cutting speed coupled with the short
cycling time have made this a popular microtome in many laboratories