3.1 - Ideas about the cause of disease and illness

• What century was a very exciting time for science?

  18th century
• How did the influence of the Church change by 1700?

  It was not as great as before
• What did many people begin to focus on instead of divine explanations?

  Developing scientific explanations
• What intellectual movement made it fashionable to seek answers about the world?

  The Enlightenment
• What was the Enlightenment?

  A movement promoting independent thought
• What did the Enlightenment challenge regarding traditional authorities?

  Control over everyday life
• What areas of life did the Enlightenment influence?

  • Politics
  • Philosophy
  • History
  • Economics
  • Science
• What was happening simultaneously with the Age of Enlightenment?

  The Scientific Revolution
• What were the two halves of the Scientific Revolution?

  1. First half: Discrediting old theories
  2. Second half: New ideas replacing old ones
• When did the second half of the Scientific Revolution begin?

  c1700
• How did society change during the 18th century?

  Cities grew as people sought jobs
• What issue arose in the new cities that were formed?

  They became dirty and disease-ridden
• What diseases posed a threat to the working population?

  Tuberculosis, typhus, and smallpox
• Why was it important to understand the causes of disease and illness?

  To protect the new working population
• What was the prevailing belief about disease causes in the 18th century?

  There were not many new ideas
• What theory was discarded in the 18th century regarding disease?

  Theory of the Four Humours
• What theory about disease was still believed in the 18th century?

  Miasma theory
• How was the theory of spontaneous generation viewed in the early 18th century?

  As an alternative to the Four Humours
• What advancement helped scientists observe microbes in the 18th century?

  Improvements in glass lenses for microscopes
• What did most people believe about microbes found on decaying matter?

  They were products of decay
• Was spontaneous generation proven correct in the 18th century?

  No, it was just a theory
• When did scientists establish a solid link between microbes and disease?

  In the 19th century
• What was Germ Theory?

  The discovery that bacteria caused decay (not decay causing bacteria).
• Background: 1660s- Leeuwenhoek and Robert Hooke

  Leeuwenhoek was the first person to see bacteria under a microscope while observing linen. Robert Hooke used a microscope to draw an image of a plant cell. Neither of them linked these bacteria and miniscule cells to disease. They thought that rotten material caused bacteria and not the other way round, which became known to be the theory of spontaneous generation. 

  -       Miasma was still a common belief for the cause and spread of disease.
• The Development of Germ Theory:

  In 1860, the French Academy of Science challenged scientists to come up with evidence to either prove or disprove the theory of spontaneous generation.

  By the middle of the 19th century, microscopes had improved even more- it was now possible to magnify substances to a much higher level and keep the image clear enough to see. Because of this, Louis Pasteur, a French scientist, was able to observe unwanted microbes in wine and vinegar, which turned both liquids ‘bad’.

  Pasteur published the results of his experiments in 1861. He called his discovery Germ Theory.
• The four basic principles of Germ Theory:

  1. The air contains living microorganisms

  2. Microbes can be killed by heating them

  3. Microbes in the air cause decay

  4. Microbes are not evenly distributed in the air
• Pasteur proved that the idea of spontaneous generation was wrong because decay did not happen to sterilised matter that was left undisturbed. Instead, something in the air was causing the decay.

  Pasteur also theorised that, as germs were causing decay, they might also be causing disease in the human body. He observed one particular type of microorganism killing off France’s silkworm population, which seemed to prove his theory. However, he did not publish this germ theory of infection until 1878.
• Pasteur’s influence in Britain

  Pasteur’s work had almost no impact on British ideas about the causes of illness and disease. He was not a doctor, and his work focused on decay and spoiled food, not disease.
• In Britain, the theory of spontaneous generation continued to be important until the 1870s. It was promoted by Dr Henry Bastian, who was one of the most powerful doctors in the country. Because he was so well-respected, few people disagreed with him.

  However, some scientists did start to look for a link between the microbes and disease. One of these as Joseph Lister, who read Pasteur’s germ theory and linked it to infection problems his surgical patients had experienced.
• John Tyndall:

  Another scientist who promoted the link between microbes and disease was John Tyndall. He had discovered that there were small organic* particles in the air. In January 1870, he gave a lecture, linking his discovery with Pasteur’s germ theory and Lister’s work on wound infection. Tyndall theorised that dust particles carried the germs that caused disease.

  However, Tyndall wasn’t a doctor, he was a physicist. The medical world trusted Bastian’s beliefs rather than Tyndall’s theory.
• Lister’s ideas were also doubted, as he could not prove his theory. Although microscopes meant that microbes were visible, there were lots of them present in the blood or in a wound. Doctors could not yet identify what they were and what role they played. The gut is a good example of why they had problems: when examined under the microscope, scientists saw hundreds of microbes, even in healthy people. It seemed impossible to people that these microbes caused disease, too.
• Therefore, Pasteur’s theory had limited impact in Britain, because attitudes among doctors meant people refused to recognise the link between germs and disease- even though the link was correct. 

  Old ideas: the SPONTANEOUS GENERATION theory claimed rotting matter CREATED microbes. 

  New ideas: Pasteur’s GERM THEORY claimed that microbes CAUSED DECAY, and were not created by rotting matter.

  Both ideas theorised that microbes were spread through MIASMATA or air.
• Robert Koch successfully identified that different germs cause many common diseases. 

  Koch discovered the bacteria that caused tuberculosis, in 1882. He then published his ideas on the methods that could be used to identify disease-causing microbes.

  1. The microbe is present in every case of the disease

  2. Once taken from the body, the microbe can be reproduced into a pure culture*.

  3. The disease can be reproduced in test animals using that culture.

  4. The microbe can be taken out of the test animals and used to start a fresh culture.
• In 1883, Koch discovered cholera, and in 1884 he proved that it was spread in water supplies when he found it in the drinking water in India, where a cholera epidemic had broken out. This also provided proof for John Snow’s theory.

  Koch made it easier for future scientists to study bacteria by developing a new method of growing them, using agar jelly in a petri dish. This made it easier to study the bacteria under a microscope. Later, Koch also developed a method for staining them with industrial dyes, to make them easier to see.
• Koch’s research inspired other scientists. Over the next two decades, they went on to discover the microbes responsible for other diseases, such as diphtheria, pneumonia, meningitis, the plague, tetanus and various other infections. Koch received the Nobel Prize for Medicine in 1905. He is considered to be the father of bacteriology* and his methods are still used when seeking out the microbes responsible for disease today.
• Koch's influence in Britain:

  The identification of microbes that caused particular diseases was an enormous breakthrough in the diagnosis of disease. Whereas before, doctors had studied and treated symptoms, not they studied the disease itself. The medical profession had begun to recognise that he microbe created the symptoms of the disease, and it was the microbe that needed to be removed. 
• Example of Koch's influence:

  1883: the microbe that caused diphtheria was found.

  Symptoms: painful cough, fever. A leathery skin would grow over the tonsils and the back of the throat, which meant that the sufferer could not breathe.

  By studying the microbe, scientists were able to observe that it produced a poison. The poison, when breathed, stayed in the throat and caused the painful symptoms. Since the microbe had been identified, scientists were able to seek ways of attacking it directly, rather than just treating the symptoms. 
• Impact of Germ Theory

  Progress in treatment and prevention using Germ Theory was slow. Once Pasteur, Koch and other scientists had found the specific disease-causing microbes, cures and vaccines could be tested. Only after this did Germ Theory begin to have a direct impact on medical treatment.
• Setbacks to Germ Theory

  Even the British government rejected the Germ Theory of disease at first. When Koch travelled to Calcutta in 1884 to study an outbreak of cholera, he proved that it was caused by microbes in the supply of drinking water. However, this was ignored by the British government. Instead, they kept to the idea that the disease was present in the soil, and the miasma was brought out by the weather. This seemed to make sense, since there was more cholera around during the rainy season.
• Despite these setbacks, in the 20th century Germ Theory and the new study of bacteriology had an enormous impact on our understanding of the causes of disease and illness. It is now recognised that many diseases are caused by a microorganism-bacteria, virus or fungus.

  When diagnosing a disease, doctors now look for symptoms and try to match them to a disease caused by a specific microbe. 

  By the end of the 19th century, the mystery around what caused illness and disease had been solved.