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106                 PA THOGENIC BA CTERIA.

The Sterilization and Protection of Instruments
and Glassware Used in Experimentation.—Steriliza-
tion may be accomplished by either moist or dry heat.
For the perfect sterilization of objects capable of with-
standing it dry heat is preferable, because more certain
in its action. If we knew just what organisms "we had
to deal with, we might be able in many cases to save
time and gas, but while some simple non-spore-producing
forms are killed at a temperature of 60° C., others can
withstand boiling for an hour ; it is therefore best to
employ a temperature high enough to kill all with cer-
tainty. Platinum wires used for inoculation are held in
the direct flame until they become incandescent. In
sterilizing such wires attention must be bestowed upon
the glass handle, which should be held in the flame for
at least half its length for a few moments when used for
the first time each day. Carelessness in this respect may
cause the loss of much time by contaminating cultures.

Knives, scissors, and forceps may be exposed for a very
brief time to the direct flame, but this affects the temper
of the steel when continued too long. They may also
be boiled, steamed, or carbolized.

All glassware is sterilized by exposure to a sufficiently
high temperature, 150° C. or 302° F., for one hour in the
well-known hot-air closet (Fig. 9). A temperature of
150° C. is sufficient to kill all known bacteria and their
spores if continued for an hour.

Rubber stoppers, corks, wooden apparatus, and other
objects which are warped, cracked, charred, or melted
by so high a temperature must be sterilized by moist
heat in the steam apparatus for at least an hour before
they can be pronounced sterile.

It must always be borne in mind that after sterilization
has been accomplished the same sources of contamination
that originally existed are still present, and begin to
operate as soon as the objects are removed from the
sterilizing apparatus.

To Schroder and Van Dusch belong the  credit  of