These
are
briefly
summarised
below:
1. Heat.
For
general
sterilisation
a
time
and
temperature
that
kill
all
organisms
including
heat-resistant
spores
is used. The methods generally adopted
are as follows:
( a) Wet
heat
in
an
autoclave.
The
usual
met/1od
is
a
time
of
30
minutes
at
a
pressure
of
1.05
kg/cm2
that
will
give
a
temperature
of
121°C. This is the best
method, if practicable.
(b) Tyndallization.
This
is
a
course
of
three
periods
of
boiling
at
100°C
for 30 min. at daily intervals.
(c) Dry
heat.
This
is
done
in
a
dry
oven,
where
a
temperature
of
160° C
for two hours is usually required.
2. Filtration.
The
liquid
or
gas
to
be
sterilised
is
passed
through
a
filter
with
a
porosity
sufficient
to
remove
any
microorganism
in
suspension.
The
cotton
wool
is
used
for
gases.
For
liquids,
a
variety
of(filters
are
available,
made
of
materials
such
as
cellulose
nitrate
(millipore
filters).
This
method
is
very
useful
for
sterilisation
of
liquids
containing
heat-labile
components.
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