Louis Pasteur by Nicola Kingsley - National STEM Centre

Anthrax bacilli
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with the disease. Outbreaks were particularly common in
dry weather. Some places, however, were seldom, if ever,
affected by the disease.
Pasteur found the microbe he believed to be responsible for
anthrax in the blood of animals suffering from the disease.
It produced spores (extra tough cells) which were so hardy
that they could survive outside the body for years.
Walking around the fields "cursed with anthrax" he
noticed many worm casts, the little piles of earth that
earthworms brought to the surface. When he looked at the
worm casts under a microscope, he found anthrax spores.
He collected earthworms and cut them up. In the soil in
their intestines were the same spores. Livestock which had
died of anthrax was buried by farmers, often many feet
deep, in the fields where it died. What was happening, he
reasoned, was that worms were carrying the spores from
the diseased carcasses buried below to the surface of the
fields. During dry weather the worm casts dried out and
the wind blew about the fine particles of soil bearing the
spores. Some landed on plants and were eaten by grazing
beasts. The reason why anthrax occurred in some places
but not others was that some places had soil so sandy or
chalky that there were very few earthworms to spread the
disease.