Louis Pasteur by Nicola Kingsley - National STEM Centre

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By 1859 no one had come any closer to resolving the
argument, and Pasteur decided that he would be the one to
do it. Some of his friends tried to persuade him not to waste
his time getting involved in a dispute which they were sure
could not be settled. Pasteur admitted that he would not be
able to prove that spontaneous generation never happened.
Somewhere in the universe life might be creating itself, but
he intended to show that there was no evidence for this.
He set·to work in his new laboratory, five small rooms in
an outbuilding at the Ecole Normale. He had persuaded
the authorities to let him have these when the two little
attic rooms he had been using became too cramped.
Scientists in those days were expected to make do with
very little and Pasteur was short of money and space for
his experimental work. He needed an incubator
(somewhere warm where microbes could be grown) and the
only place he could find to build it was the space under the
stairs. There, in a little room that was reached by crawling
on hands and knees, he spent hours every day, observing
the flasks used in his experiments.
He began by investigating the claim that fresh ~ir started
spontaneous generation. He boiled some guncotton in
water until both cotton and water were sterile (had
nothing alive in them). Then he forced fresh air through
the sterile cotton. When he put the cottorl back in sterile
water, he found microbes appeared in the water. He
dissolved the cotton in alcohol, and looked at what was
left. It turned out that the cotton had filtered dust out from
the fresh air, and the dust contained all the microbes.
Pasteur then experimented to see if'microbes could have
developed in the cotton by spontaneous generation. He
filtered air through a sterile cotton plug, and then through
a second sterile plug. When he put the second plug in
water, there were no microbes, and none developed later.
They had all been filtered out by the first plug. He
concluded that microbes could be carried in the air, but
fresh air in itself could not actually give rise to microbes.
To further prove the point he put soup in glass flasks and
then melted the top of each flask and shaped it into a long
tube that curved down and then up again, like the neck of