]
Small objects immersed in gum solutions are frozen and in condition for
cutting in less than one minute.
The method of using this microtome can be understood by reference to the
illustration. A represents a revolving plane, by which the thickness of
the section is regulated, in the center of which an insulated chamber is
secured for freezing the tissue. It resembles a pill-box constructed of
metal. A brass tube enters it on each side. The larger one is the supply
tube, and communicates with the pail, a, situated on bracket, s, by
means of the upper tube, t. To the smaller brass tube is attached the
rubber tube, t b, which discharges the cold salt water into a pail
placed under it. (See b.) The salt and water as it passes from pail, a,
to pail, b, is at a temperature of about zero. The water should not be
allowed to waste. It should be returned to the first pail for continual
use, or as long as it has freezing properties. As a matter of further
economy, it is necessary to limit the rate of exit of the freezing
water. This is regulated by nipping the discharge-tube with the spring
clothes pin supplied for the purpose. Should the cold within the chamber
be too intense, the edge of the knife is liable to be turned and the
cutting will be imperfect.
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