Louis Pasteur by Nicola Kingsley - National STEM Centre

A drop of pond
water magnified
to show various
micro-organisms
14
butterflies. Using a magnifying glass he looked for, and
found, the eggs.
A few years later, in 1677,a shopkeeper in the Netherlands,
Anton van Leeuwenhoek looked through a microscope,
which he had made in his spare time, at a drop of pond
water. He discovered lots of tiny living things, which
nobody had suspected. A few years later he made a better
microscope that allowed him to just make out even tinier
dots and rods, which he thought might also be alive. He
had found the type of microbe that was later given the
name "bacteria".
Biologists wondered if the microbes van Leeuwenhoek had
found arose, like maggots, from something else that was
alive, or if they appeared by spontaneous generation. They
discussed the matter for years. Then in 1748 an English
biologist, John Needham, set up an experiment which he
hoped would provide an answer. He took some mutton soup
and boiled it for a few minutes to kill any microbes in it.
Then he put the soup in a container which he sealed
tightly to stop any fresh microbes getting in. After a few
days he opened the container and found the soup swarming
with microbes. He decided they must have arisen from the
soup by spontaneous generation.