method. An alternative plan is to hold the
inoculated tube vertically upright between the opposed palms and to
rotate it between them by rapid backward and forward movements of the
two hands (Fig. 124).

[Illustration: FIG. 125.--Pouring plates.]

6. Sterilise the platinum loop, and add two loopfuls of diluted inoculum
to tube No. 2, and mix as before.

7. In a similar manner transfer three loopfuls of liquefied medium from
tube No. 2 to tube No. 3, and mix thoroughly.

8. Flame the plug of tube No. 1, remove it, then flame the lips of the
tube; slightly raise the cover of Petri dish No. 1, introduce the mouth
of the tube; then, elevating the bottom of the tube, pour the liquefied
medium into the Petri dish, to form a thin layer. Remove the mouth of
the tube and close the "plate." If the medium has failed to flow evenly
over the bottom of the plate, raise the plate from the levelling
platform and by tilting in different directions rectify the fault.

9. Pour plates No. 2 and No. 3, in a similar manner, from tubes Nos. 2
and 3.

10. Label the plates with the distinctive name or number of the
inoculum, also the date; the number of the dilution having been
previously indicated (step 3).

11. Place in the cool incubator for three or more days, as may be
necessary.

In this way colonies may be obtained quite pure and separate from each
other.

In plate No. 1, probably, the colonies will be so numerous and crowded,
and therefore so small, as to render it useless. In plate No. 2 they
will be more widely separated, but usually No. 3 is the plate reserved
for careful examination, as in this the colonies are usually widely
separated, few in number, and large in size.

_Agar plates_ are poured in a similar manner, but the agar must be
melted in boiling water and then allowed to cool to 45 deg. C. or 42 deg.
C. in a carefully regulated water-bath before being inoculated, and the
entire process must be carried out very rapidly, otherwise the agar will
have solidified before the operation is completed.

NOTE.--In pouring plates, since tube No. 1 (for the first
dilution) rarely gives a plate that is of any practical
value it is frequently replaced by a tube of bouillon or
sterile salt solution, and in such case plate No. 1 is not
poured.

~Surface Plates.~--

This method of pouring what may be termed "whole" plates (since colonies
may appear both on the surface and in the depths of the med