ubes of sterile nutrient media, gelatine (or agar)
previously liquefied by heating in the water-bath and cooled
to 42 deg. C., otherwise the heat of the medium would destroy
many, if not all, of the bacteria introduced.

6. Tube of cultivation to be planted from.

7. Platinum loop.

8. Bunsen burner.

9. Grease pencil.

[Illustration: FIG. 121.--Handy form of water-bath for melting tubes of
agar and gelatine previous to slanting them; or to making shake cultures
or pouring plates.]

Method of "Pouring" Plates.--

1. Place the glass dish on the levelling tripod (Figs. 122, 123); if
gelatine plates are to be poured fill the dish with ice water--gelatine
solidifies so slowly that it is necessary to hasten the process; if agar
is to be used fill with water at 50 deg. C.--agar sets almost immediately
at the room temperature and by slightly retarding the process lumpiness
is avoided; cover the dish with the square sheet of glass.

2. Place the spirit level on the sheet of glass and by means of the
levelling screws adjust the surface of the glass to the horizontal.

This leveling is an important matter since the development of a colony
is to some extent proportionate to the supply of medium available for
its nutrition. Thus in a "smear" on sloped tube culture, the colonies at
the upper part of the medium are stunted and small but increase in size
and luxuriance of growth the nearer they approach to the bottom of the
tube, where there is the greatest depth of medium.

[Illustration: FIG. 122.--Plate-levelling stand.]

3. Place three sterile Petri dishes in a row on the surface of the glass
plate and number them 1, 2, and 3, from left to right.

[Illustration: FIG. 123.--Plate-levelling stand, side view.]

4. Number the previously liquefied tubes of nutrient media 1, 2, and 3.
Flame the plugs and see that each plug can be readily removed from the
mouth of its tube.

5. Add one loopful of the inoculum to tube No. 1, treating the
liquefied medium as bouillon. After replugging, grasp the tube near its
mouth by the thumb and first finger of the right hand, and with an even
circular movement of the whole arm, diffuse the inoculum throughout the
medium; avoid jerky movements, as these cause bubbles of air to form in
the medium.

[Illustration: FIG. 124.--Mixing emulsion for plates.]

The knack of mixing evenly without producing air bubbles, is not always
easily acquired, by this