Physitemp Instruments BFS - Manual (Page 4)

5.4 To return the stage to normal it is necessary only to restore the water flow. Within seconds, the
stage will automatically switch on; this can be checked by noting that the meter is indicating current flow.
6.0 OPERATING THE EQUIPMENT
6.1 Check that cold water is flowing through the stage, as described above.
6.2 Plug the black connector plug into the socket of the right side of the Power Supply.
6.3 Place tissue specimen on the stage. If it is dry, first moisten the surface with a few drops of water
to provide better heat conduction. The thinner the specimen, the faster it will freeze. These powerful stages
will freeze a block of tissue over 1” thick, but it will take several minutes to do so. Whenever possible, tis-
sue thickness should be limited to 2-3mm. With this thickness, sectioning can commence in less than two
minutes.
6.4
SPECIMENS PRESERVED IN FORMALIN should be thoroughly washed in water before
attempting to freeze them. Formalin depresses the freezing point of water to such an extent that the speci-
men may not freeze sufficiently for sectioning even though it may be below -30
o C,
6.5 If even quicker freezing is desired, a blast of CO
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can be applied to the specimen when the Power
Supply is switched on.
6.6
Switch on the Power Supply by turning the CURRENT control clockwise. Maximum cooling is
achieved at a current of 10.5 Amps. There is no advantage in increasing current beyond this point.
6.7
When the specimen is completely frozen, commence sectioning using normal techniques. If speci-
men is too cold, reduce cooling current. See Section 8.
6.8
When sufficient sections have been made, remaining tissue is easily removed from the stage. Press
the spring-loaded switch to THAW position and hold it down until the frost on the stage surface is seen to
melt. This takes about ten seconds. Switch the Power Supply off, slide the tissue specimen from the surface
of the stage. Wipe the stage.
6.9
If the stage is being used in a Cryostat, it is essential to remove the water from its tubing. This is
most easily done by blowing gently into one of the tubes until air has replaced the water.
7.0 TYPICAL STAGE PERFORMANCE
7.1 The degree of cold obtained is dependent on the temperature of the cooling water. Thus, lower
stage temperatures are achieved in winter than in summer. At 10.5 Amperes the stage temperature should
reach 55-65
o C below that of the cooling water. Thus a stage temperature of -40 o C can be achieved under
normal conditions. A 1/2” thickness of liver which covers the stage should freeze with 15-20 minutes.
Temperature throughout the tissue should drop to -20
o C in a further 10 minutes. Tissue under 1/16” in thick-
ness should be ready for sectioning with 90 seconds after switching on.
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