se apparatus, etc., inside the oven, taking particular care
that none of the cotton-wool plugs are in contact with the walls,
otherwise the heat transmitted by the metal will char or even flame
them.

To prepare a wire crate for the reception of test-tubes,
etc., cover the bottom with a layer of thick asbestos cloth;
or take some asbestos fibre, moisten it with a little water
and knead it into a paste; plaster the paste over the bottom
of the crate, working it into the meshes and smoothing the
surface by means of a pestle. When several crates have been
thus treated, place them inside the hot-air oven, close the
door, open the ventilating slide, light the gas, and run the
temperature of the interior up to about 160 deg. C. After an
interval of ten minutes extinguish the gas, open the oven
door, and allow the contents to cool. The asbestos now forms
a smooth, dry, spongy layer over the bottom, which will last
many months before needing renewal, and will considerably
diminish the loss of tubes from breakage.

Copper cylinders and large test-tubes intended for the
reception of pipettes are prepared in a similar manner, in
order to protect the points of these articles from injury.

2. Close the oven door, and open the ventilating slide, in order that
any moisture left in the tubes, etc., may escape; light the gas below;
set the electric alarm to ring at 100 deg. C.

3. When the temperature of the oven has reached 100 deg. C., close the
ventilating slide; reset the alarm to ring at 175 deg. C.

4. Run the temperature up to 175 deg. C.

5. Extinguish the gas at once, and allow the apparatus to cool.

6. When the temperature of the interior, as recorded by the thermometer,
has fallen to 60 deg. C.--_but not before_--the door may be opened and
the sterile articles removed and stored away.

NOTE.--Neglect of this precautionary cooling of the oven to
60 deg. C. will result in numerous cracked and broken tubes.

On removal from the oven, the cotton-wool plugs will probably be
slightly brown in colour.

Metal instruments, such as knives, scissors, and forceps, may be
sterilised in the hot-air oven as described above, but exposure to 175 deg.
C. is likely to seriously affect the temper of the steel and certainly
blunts the cutting edges. If, however, it is desired to sterilise
surgical instruments by hot air, they should be pack