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At the beginning of the 19th century, though there had been some advances in medical knowledge, scientists still did not understand what caused disease.

Germ theory

Joseph Lister was able to make a much more powerful microscope than had previously been possible. This was because of improvements in the quality of the glass he could use for the lenses. His model from 1826 could magnify objects 1,000 times, which enabled scientists to see germs and bacteria in more detail than had been possible before.

The next great breakthrough came in the 1860s when Louis Pasteur, using Lister’s microscope, discovered germs and revolutionised medical knowledge. Germs were given their name because they appeared to be germinating or growing.

Louis Pasteur

In the 1850s the French scientist Louis Pasteur was employed by a brewing company to find out why its beer was going sour. Through a microscope he discovered micro-organisms growing in the liquid. He believed that these germs were causing the problem. He discovered that the microscopic bacteria that turned beer bad could be killed by heating, ie by pasteurisation.

In 1861, Pasteur published his germ theory. By 1865, had proved the link between germs and disease. In 1879, he discovered a vaccine for chicken cholera. He found that when the germ was exposed to air it weakened, and that injecting this weakened germ into chickens prevented them from catching the disease. In 1881 he developed a vaccine for anthrax, and by 1885 a vaccine for rabies.

Robert Koch

In the late 1870s, a German physician, Robert Koch, began to apply Pasteur’s ideas to human diseases. In doing so, he created the science of bacteriology. He identified the bacteria that cause anthrax, tuberculosis and cholera. Koch was very thorough. To isolate the anthrax bacteria, he transferred the bacteria through 20 generations of mice until he was satisfied that he had the right micro-organism. Koch also developed a medium for growing bacteria and a way of staining them so that they could be seen more easily.

Further developments in bacteriology

Koch’s success spurred Pasteur into action again. At the time, there was intense rivalry between France and Germany, following a war in 1870. The German government had given Koch a team of scientists to assist him. Now the French government decided to back Pasteur, who went on to develop vaccines.

In the 1880s and 1890s, rapid progress was made in identifying the bacteria that caused disease and in developing vaccines.

Governments supported scientific research with money.

Scientists like Pasteur and Koch led teams of able scientists. Emil von Behring, a member of Koch’s team, discovered anti-toxins. With Emile Roux, an associate of Pasteur, Behring used anti-toxins to develop a vaccine for diphtheria.

Paul Ehrlich, a student of Koch, produced the drug Salvarsan 606 to treat syphilis. This was the first of what became known as ‘silver bullets’ - drugs designed to target specific germs.