the steriliser itself, and provided with handles.
The top of the steriliser is hinged to form a lid.

METHOD.--

1. Place the instruments, etc., to be sterilised inside the copper
basket, and replace the basket in the steriliser.

2. Pour a sufficient quantity of water into the steriliser, shut down
the lid, and light the gas below.

[Illustration: FIG. 28.--Koch's steriliser.]

[Illustration: FIG. 29.--Arnold's steriliser.]

3. After the water has boiled and steam has been issuing from beneath
the lid for at least ten minutes, extinguish the gas, open the lid, and
lift out the wire basket by its handles and rest it diagonally on the
walls of the steriliser; the contained instruments, etc., are now
sterile and ready for use.

4. After use, or when accidentally contaminated, replace the instruments
in the basket and return that to the steriliser; completely disinfect by
a further boiling for fifteen minutes.

5. After disinfection, and whilst still hot, take out the instruments,
dry carefully and at once, and return them to their store cases.

_Streaming steam_--i. e., steam at 100 deg. C.--destroys the vegetative
forms of bacteria in from fifteen to twenty minutes, and the sporing
forms in from one to two hours. This method is chiefly used for the
sterilisation of the various nutrient media intended for the cultivation
of bacteria, and is carried out in a steam kettle of special
construction, known as Koch's steam steriliser (Fig. 28) or in one of
its many modifications, the most efficient of which is Arnold's (Fig.
29).

The steam steriliser in its simplest form consists of a tall tinned-iron
or copper cylindrical vessel, divided into two unequal parts by a
movable perforated metal diaphragm, the lower, smaller portion serving
for a water reservoir, and the upper part for the reception of wire
baskets containing the articles to be sterilised. The vessel is closed
by a loose conical lid, provided with handles, and perforated at its
apex by a tubulure; it is mounted on a tripod stand and heated from
below by a Bunsen burner. The more elaborate steriliser is cased with
felt or asbestos board, and provided with a water gauge, also a tap for
emptying the water compartment.

TO USE THE STEAM STERILISER.--

1. Fill the water compartment to the level of the perforated diaphragm,
place the lid in position, and light the Bunsen burner.

2. After the water has boiled, allow sufficient time to elapse for steam
t