has already been used is regarded as _infected_, and is
treated in a slightly different manner.

~Infected Test-tubes.~--

1. Pack the tubes in the wire basket of the autoclave (having previously
removed the cotton-wool plugs, caps, etc.), in the vertical position,
and before replacing the basket see that there is a sufficiency of water
in the bottom of the boiler. Now attach a piece of rubber tubing to the
nearest water tap, and by means of this fill each tube with water.

2. Disinfect completely by exposing the tubes, etc., to a temperature of
120 deg. C. for twenty minutes (_vide_ page 37).

(If an autoclave is not available, the tubes must be placed in a
digester, or even a large pan or pail with a tightly fitting cover, and
boiled vigorously for some thirty to forty-five minutes to ensure
disinfection.)

3. Whilst still hot, empty each tube in turn and roughly clean its
interior with a stiff test-tube brush.

4. Place the tubes in a bucket or other convenient receptacle, fill with
water and add a handful of Sapon or other soap powder. See that the
tubes are full and submerged.

5. Fix the bucket over a large Bunsen flame and boil for thirty minutes.

6. Cleanse the interior of the tubes with the aid of test-tube brushes,
and rinse thoroughly in cold water.

7. Drain off the water and immerse tubes in a large jar containing water
acidulated with 2 to 5 per cent. hydrochloric acid. Allow them to remain
there for about fifteen minutes.

8. Remove from the acid jar, drain, rinse thoroughly in running water,
then with distilled water.

9. Invert the tubes and allow them to drain completely.

Dry the tubes and polish the glass inside and out with a soft cloth,
such as selvyt.

~Infected flasks, plates, and capsules~ must be treated in a similar
manner.

~Flasks~ which have been used only in the preparation of media must be
cleaned immediately they are finished with. Fill each flask with water
to which some soap powder and a few crystals of potassium permanganate
have been added, and let boil over the naked flame. The interior of the
flask can then usually be perfectly cleaned with the aid of a flask
brush, but in some cases water acidulated with 5 per cent. nitric acid,
or a large wad of wet cotton-wool previously rolled in silver sand, must
be shaken around the interior of the flask, after which rinse thoroughly
with clean water, dry, and polish.

~Infected Pipettes.~--

1. Plunge infected pipett