e agar or the like.

2. Pour each tube into a separate Petri dish and allow it to solidify.

3. When quite solid invert each dish, raise the bottom half and rest it
obliquely on its inverted cover (Fig. 128) and place it in this position
in an incubator at 60 deg. C. for forty-five minutes (or in an incubator
at 42 deg. C. for two hours). This evaporates the water of condensation
and gives the medium a firm, dry surface.

4. On removing the plates from the incubator close each dish and place
it--still upside down--on the laboratory bench.

[Illustration: FIG. 128.--Drying surface plate of agar.]

5. Inoculate the plates in series of three, as described for gelatine
surface plates 3-8.

Hanging-drop Cultivation.

~Apparatus Required.~--

Hanging-drop slides.
Cover-slips.
Section rack (Fig. 75).
Blotting paper.
Bell glass to cover slides.
Original culture.
Tubes of broth, or liquefied gelatine or agar.
Forceps.
Platinum loop.
Bunsen burner.
Grease pencil.
Sterile vaseline.
Lysol.

(a) ~Fluid Media.~--

1. Prepare first and second dilutions of the inoculum as directed for
plate cultivations (_vide_ pages 228-229, sections 4 to 6), substituting
tubes of nutrient broth for the liquefied gelatine.

2. Sterilise a hanging-drop slide by washing thoroughly in water and
drying, then plunging it into a beaker of absolute alcohol, draining off
the greater part of the spirit, grasping the slide in a pair of forceps,
and burning off the remainder of the alcohol in the flame.

3. Place the hanging-drop slide on a piece of blotting paper moistened
with 2 per cent. lysol solution and cover it with a small bell glass
that has been rinsed out with the same solution and _not dried_.

4. Raise the bell glass slightly and smear sterile vaseline around the
rim of the metal cell by means of a sterile spatula of stout platinum
wire.

5. Remove a clean cover-slip from the alcohol pot with sterile forceps
and burn off the alcohol; again raise the bell glass and place the
sterile cover-slip on the blotting paper by the side of the hanging-drop
slide.

6. Remove a drop of the broth from the second dilution tube with a large
platinum loop; raise the bell glass and deposit the drop on the centre
of the cover-slip. Sterilise the loop.

7. Raise the bell glass sufficiently to allow of the cover-slip being
grasped with forceps, inverted, and adjusted over the cell of