Before the 1860s, scientists actually believed that decaying matter created germs, not the other way around! This disproven theory, known as Spontaneous Generation, was finally overturned by the French chemist Louis Pasteur.
In 1857, while investigating why brewery liquids turned sour, Pasteur discovered that microorganisms caused fermentation. He published his Germ Theory in 1861, proving that microbes in the air caused decay. Pasteur demonstrated this using his famous swan-neck flask experiment:
Pasteur's work soon expanded from decay to disease. In 1865, he found the first link between germs and animal disease by identifying a microbe killing silkworms. By 1878, he published his Germ Theory of Infection, arguing that germs caused illness in humans.
Pasteur also transformed treatment by developing vaccines. His major milestones included:
You can know a criminal exists, but it takes a detective to systematically track them down and prove their guilt. While Pasteur proved that germs caused disease in general, the German doctor Robert Koch founded the science of Bacteriology. He achieved this by identifying the specific Pathogen responsible for individual diseases.
Koch engaged in Microbe Hunting, developing rigorous scientific methods to isolate and study bacteria. To prove a specific microbe caused a specific disease, he developed Koch's Postulates, a systematic 4-step method:
To achieve this, Koch relied on key technical innovations:
Using these methods, Koch linked specific bacteria to deadly diseases. His major breakthrough discoveries included:
This work was heavily fueled by national rivalry. Following the Franco-Prussian War (1870-1871), the French and German governments heavily funded Pasteur and Koch to prove their nation's scientific superiority.
Understanding how diseases spread explains why our modern hospitals use sterile equipment and our cities have clean water systems. The discoveries of Pasteur and Koch caused a fundamental shift in medical practice. Doctors moved away from treating symptoms caused by "bad air" (miasma) towards targeting specific microbes.
In surgery, Germ Theory had an immediate impact on patient survival:
In public health, Koch's identification of waterborne pathogens provided the undeniable scientific proof needed for the 1875 Public Health Act. This forced local councils to provide clean water and sewers, permanently ending the government's laissez-faire attitude to public health.
Every time you take a targeted medicine, you are benefiting from a concept first dreamt up over a century ago. Paul Ehrlich, a former member of Koch's team, wanted to find a chemical cure that would act internally. He aimed to destroy an infection without harming the patient.
Ehrlich was inspired by the body's natural Antibodies, which target specific bacteria. He theorised the concept of Selective Toxicity: if Koch's chemical dyes could target and stain specific bacteria, then synthetic chemicals could be designed to kill those same bacteria. Ehrlich called this theoretical targeted compound a Magic Bullet, establishing the new field of Chemotherapy.
The search for the first synthetic cure focused on syphilis, after its bacterium was identified in 1905:
Salvarsan 606 was a groundbreaking discovery, but it had significant limitations. Because it was an arsenic-based compound, it was painful to inject and could be lethal if the dosage was incorrect. Despite these limitations, Ehrlich's breakthrough paved the way for future medical discoveries, such as Gerhard Domagk's discovery of Prontosil (a red dye) in 1932 to cure blood poisoning.
Students often confuse Magic Bullets with modern antibiotics. Remember that Magic Bullets (like Salvarsan 606 and Prontosil) are synthetic chemicals, whereas antibiotics (like Penicillin) are derived from living microorganisms like mould.
In 'Explain the significance' questions, examiners expect you to link Pasteur and Koch's discoveries to three wider areas of medicine: Treatment (vaccines), Surgery (Lister and aseptics), and Public Health (providing evidence for the 1875 Act).
Do not underestimate the role of national rivalry; explicitly mention how the Franco-Prussian War (1870-1871) accelerated medical discoveries by forcing the French and German governments to heavily fund Pasteur and Koch.
When describing Pasteur's Swan-Neck Flask experiment, clearly state that the neck allowed air in but trapped the microbes, as this proved that the germs came from the air and did not spontaneously generate.
Spontaneous Generation
The disproven medical belief that living organisms, such as disease-causing microbes, could emerge spontaneously from non-living, decaying matter.
Germ Theory
The scientific theory that many diseases are caused by the presence and actions of specific microorganisms in the body.
Attenuation
The laboratory process of weakening a pathogen so that it can be safely used to create a vaccine.
Bacteriology
The systematic scientific study of bacteria, a medical field pioneered by Robert Koch.
Pathogen
A specific microscopic organism, such as a bacterium or virus, that enters the body and causes a disease.
Microbe Hunting
The systematic, scientific search for and identification of the specific pathogens responsible for particular diseases.
Koch's Postulates
A four-step scientific method developed by Robert Koch to systematically prove that a specific microbe causes a specific disease.
Pure Culture
A laboratory culture containing only a single species of microorganism, allowing scientists to study its specific effects without contamination.
Antiseptic Surgery
The medical practice of using chemicals, like carbolic acid, to kill germs that are already present in a wound or operating theatre.
Aseptic Surgery
The medical practice of creating a completely germ-free environment to prevent infection before an operation even begins.
Antibodies
Natural substances produced by the body's immune system that target and destroy specific invading bacteria.
Selective Toxicity
The ability of a chemical substance to be toxic to a harmful microorganism without damaging the human patient's healthy cells.
Magic Bullet
A synthetic chemical compound designed to target and kill a specific pathogen without harming the host's body.
Chemotherapy
The medical treatment of a disease using synthetic chemical substances.
Salvarsan 606
The world's first magic bullet, an arsenic-based chemical compound discovered in 1909 that successfully cured syphilis.
Put your knowledge into practice — try past paper questions for History
Spontaneous Generation
The disproven medical belief that living organisms, such as disease-causing microbes, could emerge spontaneously from non-living, decaying matter.
Germ Theory
The scientific theory that many diseases are caused by the presence and actions of specific microorganisms in the body.
Attenuation
The laboratory process of weakening a pathogen so that it can be safely used to create a vaccine.
Bacteriology
The systematic scientific study of bacteria, a medical field pioneered by Robert Koch.
Pathogen
A specific microscopic organism, such as a bacterium or virus, that enters the body and causes a disease.
Microbe Hunting
The systematic, scientific search for and identification of the specific pathogens responsible for particular diseases.
Koch's Postulates
A four-step scientific method developed by Robert Koch to systematically prove that a specific microbe causes a specific disease.
Pure Culture
A laboratory culture containing only a single species of microorganism, allowing scientists to study its specific effects without contamination.
Antiseptic Surgery
The medical practice of using chemicals, like carbolic acid, to kill germs that are already present in a wound or operating theatre.
Aseptic Surgery
The medical practice of creating a completely germ-free environment to prevent infection before an operation even begins.
Antibodies
Natural substances produced by the body's immune system that target and destroy specific invading bacteria.
Selective Toxicity
The ability of a chemical substance to be toxic to a harmful microorganism without damaging the human patient's healthy cells.
Magic Bullet
A synthetic chemical compound designed to target and kill a specific pathogen without harming the host's body.
Chemotherapy
The medical treatment of a disease using synthetic chemical substances.
Salvarsan 606
The world's first magic bullet, an arsenic-based chemical compound discovered in 1909 that successfully cured syphilis.