2. What was the ‘Germ Theory?’
Our learning objectives today are:
To explain ideas about disease in the 18th C.
To investigate how Pasteur discovered germs
To explain why this discovery
was an important development

3. How did people explain disease before 1750?
God
People had thought it was a punishment from God.
However the church’s power was weakened and this idea was fading
4 Humours
Like spiritual explanations, this idea of humour imbalances was fading fast
Why had these theories been so popular?
Bad air (miasma)
People could see rotting food and waste in the streets and knew they smelt terrible.
They assumed it must be the smell that caused disease

4. People thought that bad air caused disease. This was called a “miasma”.
Industrial towns were more crowded and dirtier than ever. There were epidemics of diseases like TB, diphtheria and cholera and this theory seemed very logical.

5. Spontaneous Generation!
Bad air (miasma)
People could see rotting food and waste in the streets and knew they smelt terrible.
They assumed it must be the smell that caused disease
Spontaneous Generation!
The latest theory. The microscopes picked up bacteria on decaying matter.
Scientists thought that the germs were spontaneously (automatically) generated (created) by the decay and then spread the disease further.
Is this right? What is wrong with this theory?

6. Louis Pasteur!
The Daddy of Bacteriology.

7. He thought it was because of germs.
Pasteur was a French scientist, asked by a brewery to investigate why their alcohol was going sour.
He thought it was because of germs.
He proved that germs in the air were causing the decay – not the other way around …

8. 100 years later, it was still sterile (no germs)!
He took two flasks – he heated the liquid in one flask to kill the germs and make it sterile.
He then drove the air out so no more bacteria could grow, and sealed the flask.
100 years later, it was still sterile (no germs)!
The other flask soured with the bacteria.

9. He called this method of heating and sterilising liquids …
Pasteurisation!
Many foods are pasteurised, such as milk. This method also paved the way for air-tight food storage such as vacuum packing and air-tight jars, tin cans etc.

10. He was asked to investigate a disease in silkworm.
He proved that bacteria was spreading the disease and therefore linked germs to disease (in animals)

11. He proved that germs caused diseases in other animals too.
He accidentally injected a chicken with some old chicken cholera germs.
The chicken did not die!
He then injected the chicken with fresh germs, and it still didn’t die!
He had proved how Jenner’s vaccination worked.
He now wanted to prove germs caused human diseases too …

12. Learning check: Title – Louis Pasteur and Germ Theory
Write down these key words (underline) and a definition for each:
Miasma
Spontaneous generation
Germ Theory

13. Your Task
Create a poster advertising pasteurised milk. The point of it is to explain germ theory so you need to include the following:
What germs are (tiny organisms)
Where germs come from (they are in the air, they grow on things, they cause disease!)
How germs and milk are linked (germs turn it sour)
How the process of pasteurisation works
Who it is named after and why!

14. Learning check:
Swap posters with the person next to you
In pencil (on the back) give it one star and a wish
Homework – finish your Pasteurisation poster for next Wednesday please!!