🔬 The target
Ehrlich chose syphilis. In 1905 scientists identified the bacterium that causes it. Now there was a known germ to aim at. Until then, the usual treatment was mercury, a poison that could harm the patient as well.
Accelerating Change, 1875-1905: Ehrlich, Koch and Chemistry » Blood Groups, Magic Bullets and Paul Ehrlich
What you'll learn this session
Study time: 30 minutes
Edexcel spec: Paper 2 Section B, Breadth study B2, Key topic 3
- Why blood transfusions so often failed, and how Landsteiner's discovery of blood groups in 1901 helped
- What Paul Ehrlich meant by a "magic bullet"
- How the search for a chemical cure led to Salvarsan 606
- How to answer an 8-mark "Explain TWO causes" question
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Unlock This CourseThe problem with blood transfusions
A blood transfusion means putting blood from one person into the body of another. It sounds simple, and it could save a patient who had lost a lot of blood, for example after an operation or childbirth. In 1818 a London doctor, James Blundell, gave the first recorded transfusion from one person to another. But for the next eighty years transfusions were a gamble. Sometimes the patient recovered. Often the patient got worse and died, and nobody knew why.
The answer was found in 1901 by an Austrian doctor, Karl Landsteiner. He mixed samples of blood from different people and watched what happened. In some mixtures the blood stayed smooth. In others the red blood cells stuck together in clumps. Landsteiner worked out that people's blood is not all the same. He sorted it into different types, now called the blood groups A, B and O. A fourth group, AB, was found soon afterwards.
Key terms:
- Transfusion: putting blood from one person (the donor) into the body of another person.
- Blood group: a type of blood. Mixing the wrong groups makes the blood clump together, which can kill.
Why blood groups mattered
Landsteiner's discovery explained the earlier deaths. When a patient was given blood from the wrong group, the blood clumped inside the body, and this could be fatal. When the groups matched, the transfusion was much safer. Doctors could now test a patient's blood group and a donor's blood group before they began, and choose a match.
The discovery did not change medicine overnight. It took years for blood testing to become routine, and storing blood so it was ready when needed was still a problem. Landsteiner was given a Nobel Prize for his work in 1930. Transfusions came to play a much bigger part in medicine later, especially in war (see the lesson on blood transfusion and fighting infection in the First World War).
Paul Ehrlich and the "magic bullet"
Paul Ehrlich was a German scientist who worked on the same problem as Pasteur and Koch: how to fight diseases caused by germs. By the 1880s Koch's team could stain bacteria with dyes, so that they showed up under a microscope. Ehrlich noticed that a dye could pick out one kind of cell or bacterium and leave the cells around it alone.
This gave him a big idea. If a dye could attach itself to a particular germ, then perhaps a chemical could be found that attached itself to that germ and killed it, without harming the patient's own body. He called this a magic bullet: a chemical that hits the germ and nothing else.
This was a new way of thinking. Vaccines, like those of Pasteur, helped the body to defend itself. Ehrlich wanted to find a drug, made by chemists, that attacked one disease directly.
Key terms:
- Magic bullet: Ehrlich's idea of a chemical that kills the germs causing one disease without harming the patient.
- Syphilis: a serious disease, spread by close contact, caused by a bacterium. It could damage the body for years.
- Salvarsan 606: the chemical cure for syphilis found by Ehrlich's team.
The search for Salvarsan 606
🧪 The search
Ehrlich's team made and tested hundreds of chemicals, many of them based on arsenic. Each one was tried on infected animals to see if it killed the germ without killing the animal.
One of Ehrlich's helpers, a Japanese bacteriologist called Sahachiro Hata, did much of the careful testing. In 1909 they found that the 606th compound they had tried worked. It was tested on patients and in 1910 it went on sale as Salvarsan. It was the first chemical drug made to target one particular disease. Ehrlich also shared a Nobel Prize in 1908 for his work on how the body fights disease.
How successful was Salvarsan?
- Success: it gave doctors a real treatment for a widespread disease, safer than mercury.
- Limits: it contained arsenic, so it could have side effects. It had to be injected, which was difficult, and treatment took a long time. Some patients were not cured.
- Lasting impact: Ehrlich showed that scientists could search for chemical cures, and this idea led to later drugs. The next big step was penicillin (see the lesson on Fleming and the discovery of penicillin).
What changed and what stayed the same
- Change: science and technology were now helping medicine to find cures, and doctors could make transfusions safer by testing blood.
- Continuity: many diseases still had no cure, and the new ideas reached patients slowly. Salvarsan was only for syphilis.
Common mistakes
- Saying Landsteiner invented blood transfusions. They were tried long before 1901. He discovered blood groups, which made them safer.
- Thinking a magic bullet is a vaccine. A vaccine helps the body defend itself. A magic bullet is a chemical that attacks the germ.
- Writing that Salvarsan was a perfect cure. It had side effects and was hard to use.
Exam-style question
Explain TWO causes of the development of Salvarsan 606 by 1910. [8 marks]
Remember: one cause alone cannot score more than half marks, so make sure you explain two.
Model answer
One cause was the work of Pasteur and Koch on germs. Their work showed that diseases are caused by particular bacteria, and in 1905 scientists identified the bacterium that causes syphilis. This gave Ehrlich a clear target to aim at. Without a known germ he could not have tested whether a chemical killed it, so the search for a cure for syphilis, which ended with Salvarsan, only became possible because of this knowledge.
A second cause was Ehrlich's idea of the magic bullet, which grew out of the staining of bacteria with dyes. He saw that a dye could attach to one kind of cell and not others, and reasoned that a chemical could be found that would kill a germ and leave the patient unharmed. This led his team, with Sahachiro Hata, to test hundreds of arsenic-based compounds on infected animals one by one, until the 606th worked in 1909. His idea gave the search a clear direction and led straight to Salvarsan.
What lifts this to the top level: each cause is backed with precise facts (1905, the dyes, Hata, the 606th compound) and the answer explains how each cause led to Salvarsan.
Exam tip
Begin each paragraph with the cause, add a date or a name, then finish by linking back to the question, for example "This led to Salvarsan because...".