surface.

5. Plant the remainder of the tubes in the series as "smears" like tube
No. 1.

6. Label with distinctive name or number, and date; incubate.

The growth that ensues in the first two or three tubes of the series
will probably be so crowded as to be useless. Toward the end of the
series, however, discrete colonies will be found, each of which can be
transferred to a fresh tube of nutrient medium without risk of
contamination from the neighbouring colonies.

~"Working" up Plates.~--

Having succeeded in obtaining a plate (or tube cultivation) in which the
colonies are well grown and sufficiently separated from each other, the
process of "working up," "pricking out," or "fishing" the colonies in
order to obtain subcultures in a state of purity from each of the
different bacteria present must now be proceeded with.

Occasionally it happens that this is quite a simple matter. For example,
the original mixed cultivation when examined microscopically was found
to contain a Gram positive micrococcus, a Gram positive straight
bacillus and a Gram negative short bacillus. The third gelatine plate
prepared from this mixture, on inspection after four day's incubation,
showed twenty-five colonies--seven moist yellow colonies, each sinking
into a shallow pit of liquefied gelatine, fourteen flat irridescent
filmy colonies, and four raised white slimy colonies. A film preparation
(stained Gram) from each variety examined microscopically showed that
the yellow liquefying colony was composed of Gram positive micrococci;
the flat colony of Gram positive bacilli and the white colony of gram
negative bacilli. One of each of these varieties of colonies would be
transferred by means of the sterilised loop to a fresh gelatine culture
tube, and after incubation the growth in each subculture would
correspond culturally and microscopically with that of the plate colony
from which it was derived,--the object aimed at would therefore be
achieved.

Usually, however, the colonies cannot be thus readily differentiated,
and unless they are "worked up" in an orderly and systematic manner much
labour will be vainly expended and valuable time wasted. The following
method minimises the difficulties involved.

(A) Inspection.

a. Without opening the plate carefully study the various colonies with
the naked eye, with the assistance of a watchmaker's lens or by
inverting the plate on the stage of the microscope and viewing with the
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