Louis Pasteur's Germ Theory

Who was Louis Pasteur?

Louis Pasteur was a French scientist who discovered germs and proved a direct connection between germs and disease.

When was Pasteur's germ theory published?

Louis Pasteur published his work on germ theory in 1861. In 1878, he published the next stage of his theory - that germs caused infection.

What was Pasteur's germ theory?

This was the theory that germs caused disease. It disproved previous beliefs about other causes, such as miasma.

What are the principles Pasteur's theory?

There were four basic principles of germ theory.

• ❖ The air contains living microorganisms.
• ❖ Microbes in the air cause decay.
• ❖ Microbes are not evenly distributed in the air.
• ❖ Microbes can be killed by heating them.

What led to Pasteur's germ theory?

In 1857, Pasteur was employed by a French brewery to work out why their beer kept going sour.

How did Pasteur make his discovery?

Using a microscope, he discovered microorganisms growing in the liquid. He realised that sterilising water, and keeping it in a sealed flask, prevented microorganisms from entering it. If the sterilised water was kept in an open flask, the microbes would breed again.

What was Pasteur's process of 'pasteurisation'?

Pasteur called the process of heating liquid to kill bacteria 'pasteurisation'.

How did Pasteur make the link between germs and disease?

In 1865, Pasteur was asked to investigate a problem in the silk industry. He discovered that silkworms were dying from microorganisms and subsequently made the link between germs and disease.

Why did doctors oppose Pasteur's theory?

Because microorganisms could be seen everywhere, for example in human blood, doctors could not understand why some caused disease and others did not.

What was the impact of Pasteur's germ theory?

There were 4 main results of germ theory.

• ❖ It demonstrated the belief that disease was created by spontaneous generation was wrong. However, spontaneous generation was still an influential idea that some doctors, such as Dr Henry Bastian, still supported.
• ❖ Between 1876 and 1883, Robert Koch discovered that different bacteria cause different diseases.
• ❖ It led to an understanding of why infection occurred in surgery.
• ❖ It led to Lister's use of carbolic acid as an antiseptic in surgery.

How did Pasteur discover a vaccine for chicken cholera?

The chicken cholera vaccine was discovered by chance in 1879. A mistake by Pasteur's assistant led to the realisation that the germ was weakened when exposed to air. Injecting the weakened germ into chickens stopped them from catching the disease.

How did Pasteur help the development of vaccines?

Pasteur helped discover two other vaccines.

• ❖ In 1881, Pasteur's team produced a weakened strain of anthrax that would prevent the disease in sheep.
• ❖ In 1885, Pasteur successfully cured a boy from rabies by using a vaccine for the disease he had developed.

How did Pasteur's rivalry with Koch lead to scientific breakthroughs?

There are 5 main reasons why the rivalry between Pasteur and Koch led to scientific breakthroughs.

• ❖ Both were researching during the Franco-Prussian War, and defeating diseases could have a big impact on the battlefield.
• ❖ The governments of France and Germany paid for the laboratories and teams of scientists, for Pasteur and Koch respectively.
• ❖ The individual characters of both men played a role. Both were relentless in their attempts to make scientific advances. For Pasteur, this resulted in his scientific breakthrough about germ theory; and for Koch it resulted in his discoveries about tuberculosis (TB) and cholera.
• ❖ Communication increased the rivalry, as Koch heard about Pasteur's discoveries quickly, helping him to make breakthroughs of his own.
• ❖ Teamwork and rivalry contributed to breakthroughs, as both sides quickly wanted to discover vaccinations for contagious diseases such as diphtheria.