STERILIZATION AND DISINFECTION.

109

kill many spores, so that the exposure of culture-media
to streaming steam is of little use unless applied in
a systematic manner—intermittent sterilization—based
upon a knowledge of sporulation.

In carrying out the intermittent sterilization the cul-
ture-medium is exposed for fifteen minutes to the passage
of streaming steam in the apparatus or to some tem-
perature judged to be sufficiently high, so that the bac-
teria contained in it are killed. As the spores remain
uninjured, the medium is stood aside in a cool place for
twenty-four hours, and the spores allowed to develop into
perfect bacteria.

When the twenty-four hours have passed the culture-
medium is again placed in the apparatus and exposed to

FIG. 12.—Autoclave for rapid sterilization Fio. 13.—Kny-Sprague steam sterilizer,
by superheated steam under pressure.

the same temperature, until these newly-developed bac-
teria are also killed. Eventually, the process is repeated