GCSE · History · AQA · Spec 8145

Germ Theory and Pasteur, Koch, Ehrlich

When milk goes off, bacteria are always there. But which way round is it: do bacteria make it rot, or does rotting make bacteria? That question split 19th-century science.

History · Cause & effect

From 'germs cause decay' to the first magic bullet

Tap each event in order. On the left: what led to it. On the right: what it led to.

Causes ←

What led here

Koch's proof that specific bacteria cause particular diseases is exactly what Pasteur couldn't supply.
The physicist John Tyndall has been lecturing on Koch's findings since 1876.

Event

Britain won over

1879

Koch's work is translated into English.

→ Consequences

What followed

Many British doctors are convinced. By the end of the 19th century, most British doctors accept Germ Theory.

Three answers to one puzzle

Tap each explanation and set it against the others.

What causes decay and disease?

Miasma

  • Ill health is caused by bad air.
  • Still widely accepted in the 19th century. Even in the 1880s, official explanations blamed miasma for a typhoid outbreak in Wales.

Spontaneous generation

  • Microbes are the result of decay, not its cause.
  • Microbes found where there is disease are produced by the disease. They didn't cause it.
  • All microbes are essentially the same.

Germ Theory

Louis Pasteur, developed further by Robert Koch

  • Microbes reach things from outside, and they are the real cause of decay.
  • Bacteria cause some human diseases.
  • As Koch later proved: specific microbes cause particular diseases.

Common ground

  • All three are trying to solve the same puzzle: why things go off, and why people fall ill.
  • Spontaneous generation and Germ Theory agree that microbes exist. A microbe is any living organism too small to be seen without a microscope. They disagree about what microbes do.

Compare the positions, then weigh them yourself.

What happened next

Pasteur's experiments disproved spontaneous generation. Predict his result below. Miasma lasted longer: officials were still using it in the 1880s.

Comparing 3 positions: Miasma, Spontaneous generation, Germ Theory.

Predict, then check

What would each theory expect to happen to the sealed liquid?

Pasteur boils two samples of the same liquid, which removes the bacteria from both. He keeps one sealed from the air and leaves the other exposed to the air. What happens?

Britain splits over Germ Theory

For many years British doctors were divided. Toggle between the two sides.

For Germ Theory

Against Germ Theory

Tap a claim from either side to see the evidence behind it.

Treating syphilis: the poison and the magic bullet

Mercury (before 1900)vsSalvarsan 606 (1909)

Start with the top row. It's the difference that gave Salvarsan 606 its name.

Focus

What it did to the patient

Mercury (before 1900)

Toxic. Some patients died of mercury poisoning rather than the disease.

Salvarsan 606 (1909)

Effective against syphilis without harming the body.

The insight

This is the whole difference. With mercury, the treatment itself could kill you. Salvarsan 606 spared the patient.

Did it attack the microbe?

Mercury (before 1900)

Yes. It attacked microbes.

Salvarsan 606 (1909)

Yes. It worked against syphilis.

Called a magic bullet?

Mercury (before 1900)

No. Attacking the microbe wasn't enough while the treatment could poison the patient.

Salvarsan 606 (1909)

Yes, the first of its kind. It inspired research into other magic bullets.

Your turn: explain it

Explain why Koch's work was important in the development of Germ Theory. [4 marks]

0 words · your answer stays on this page and is not sent anywhere.

WHAT YOU'VE LEARNED

A quick recap of today's lesson.

Bacteria are always there when milk goes off. But are they the cause of the rot, or the result of it? Answering that took a chain of scientists, each picking up exactly where the last got stuck.

What you need to know

  • Pasteur's experiments disproved spontaneous generation: microbes from outside cause decay. He called this Germ Theory.
  • Pasteur couldn't identify which bacteria caused which disease. Koch's 1876 anthrax work gave the first proof that specific bacteria cause particular diseases.
  • Many British doctors rejected Germ Theory at first. Koch's proof won most of them over by the end of the 19th century.
  • Germ Theory gave Pasteur a method for vaccines that others could copy (chicken cholera 1879, rabies 1885), but no treatment that destroyed microbes inside the body before 1900.
  • In 1909 Hata, repeating Ehrlich's experiments, showed that Salvarsan 606 treated syphilis without harming the body: the first magic bullet.

The big picture

Pasteur's experiments showed that microbes from outside cause decay (his Germ Theory), but he couldn't say which bacteria caused which disease, so many British doctors stayed unconvinced. Koch supplied that proof in 1876 by giving mice anthrax from a pure culture, and his work won most British doctors over by the end of the century. Germ Theory let Pasteur make vaccines by a method others could copy, but no treatment destroyed microbes inside the body until Hata's 1909 test of Ehrlich's Salvarsan 606, the first magic bullet.

Key points

1Three explanations competed: miasma (bad air), spontaneous generation (decay makes microbes) and Germ Theory (microbes cause decay).
2Pasteur: germs cause decay, but he couldn't say which germ causes which disease.
3Koch, 1876: anthrax in mice was the first proof of a specific germ for a specific disease. Cholera and tuberculosis followed.
4Britain was split, with Tyndall for and Bastian against. Koch's proof turned most doctors in favour.
5Vaccines came before cures. Nothing destroyed microbes inside the body until Salvarsan 606 in 1909.

Worked example

Problem

'Germ Theory changed medicine straight away.' How far is this true of the years up to 1900? Work it out step by step.

⚠ Watch out

Giving Pasteur credit for proving which germ causes which disease. That was Koch, in 1876, with anthrax. It was also the proof that convinced British doctors when Pasteur's work hadn't.

🧠

Memory hook

Pasteur: 'germs cause it.' Koch: 'THIS germ causes THIS disease.' Ehrlich and Hata: 'this chemical kills this germ, but not the patient.'

✓

Check yourself

Cover the page and answer: what could Koch show in 1876 that Pasteur never could, and why did that difference matter to British doctors?

Flashcards

(16)
What was miasma?
The idea that ill health is caused by bad air. It was still widely accepted in the 19th century. In the 1880s, official explanations blamed it for a typhoid outbreak in Wales.
What is a microbe?
Any living organism too small to be seen without a microscope.
What did spontaneous generation claim?
Microbes are the result of decay, and microbes at a site of disease are a result of the disease, not its cause. Its supporters assumed all microbes were essentially the same.
How did improved microscopes help in the 19th century?
Higher magnification and clearer images helped scientists begin spotting microbes.
What did Pasteur's boiled-liquid experiments show?
Boiling removed bacteria. Kept sealed from air, the liquid stayed fresh. Exposed to air, bacteria reappeared and it went off.
What did Pasteur's Germ Theory claim?
Microbes reach things from outside and are the real cause of decay. He also argued that bacteria cause some human diseases.
What could Pasteur NOT do?
Identify which specific bacteria caused particular diseases.
What did Koch do in 1876?
He stained and grew a pure culture of the bacteria he thought caused anthrax, then injected mice. When they developed anthrax, it was the first proof that specific bacteria cause diseases.
Why did Koch's work on cholera and tuberculosis matter?
It proved Germ Theory applied to human diseases, and that specific microbes cause particular diseases.
Who was John Tyndall?
A physicist and early, vocal supporter of Germ Theory. His own experiments suggested dust in the air carried microbes that could cause decay and spread disease.
What was Henry Charlton Bastian's argument?
Bacteria were so common in the body and elsewhere that they could hardly be causes of disease. He supported spontaneous generation throughout the 1860s.
How did Koch's ideas reach British doctors?
Tyndall lectured on Koch's findings from 1876, and Koch's work was translated into English in 1879. By the end of the century most British doctors accepted Germ Theory.
What were Pasteur's two famous vaccines?
Chicken cholera (1879): a weakened strain gave chickens immunity, the first animal vaccine. Rabies (1885): used successfully on a human for the first time.
Why was Pasteur's vaccine method a step beyond Jenner's?
Nobody understood how Jenner's smallpox vaccine worked. Pasteur used weakened strains of an identified microbe, so other scientists could copy the method.
What was wrong with treating syphilis with mercury?
Mercury attacked microbes but was toxic. Some patients died of mercury poisoning rather than the disease.
Why was Salvarsan 606 called a magic bullet?
Tested by Hata in 1909, repeating Ehrlich's experiments, it worked against syphilis without harming the body. It was the first magic bullet.

Tap any card to flip it, or use Study as deck to go through them one at a time. In the full lesson these run as a spaced-repetition deck — you rate each card Hard, Good or Easy and the tricky ones keep coming back until they stick.

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