The Development of Germ Theory Facts & Worksheets

Let’s learn more about the Germ Theory!

• Germ Theory is currently the most widely accepted scientific theory for many diseases across the globe. It simply states that microorganisms known as pathogens or “germs”, which exist in various conditions, can lead to disease. It has roots in the Middle Ages era.
• However, it really increased in prominence throughout the 19th and 20th centuries when industrialisation led to a rapid increase in the level of germs surrounding people at home and those at work. It took off with the study of numerous widespread diseases common in the 19th century including most prominently tuberculosis and cholera. The scientist most credited with the disease is Dr John Snow, who was the first to make a scientific link between water pollution and cholera epidemics in Victorian London and Louis Pasteur who would prove it in France.
• Apart from Louis Pasteur, several European researchers were particularly crucial to the development of the Germ Theory. They include Agostino Bassi, Ignaz Semmelweis, Gideon Mantell, John Snow, Robert Koch, and Joseph Lister.
• Semmelweis, Lister, and Snow were only retrospectively acknowledged for their achievements and discoveries in the field of Germ Theory.
• It was Louis Pasteur, in the 1860s, and then Robert Koch in the years that followed that conducted the laboratory experiments to provide scientific proof of the theory and open the door to research into disease-causing germs and lifesaving treatments.

Before the germs: Early mentions of the theory

• The earliest recorded mentions or theories on the links between sanitary conditions and illness go back to the Middle Ages.
• In 1025, the Persian physician Ibn Sina proposed a form of contagion theory to medicine in the medieval Islamic world.
• He outlined the classical miasma theory and attempted to blend it into his very own form of a contagion theory. He argued that people can transmit diseases to one another by breath as well as being spread by water and dirt.
• But, while there are traces of the logic behind germ theory arising earlier, this strand of medical research and theory really took off in the 19th century.
• Whilst conducting a whole series of experiments between 1808 and 1813, the Italian researcher Agostino Bassi became the very first person to prove that a disease was caused by a microorganism.
• Then in 1847, the Hungarian obstetrician Ignaz Semmelweis first made the connection between puerperal fever and examinations of delivering women by doctors.
• Having realized that there were sanitary issues as doctors would often jump from one task to another (like an autopsy to a delivery), Dr Semmelweis fundamentally changed the sanitation conditions in his hospital.

Cholera epidemic and Dr. John Snow

• Dr John Snow was infamously very sceptical of the miasma theory of illness, which was still fairly dominant in the first half of the 19th century. Although, in his era, the germ theory of disease, which was pioneered by Girolamo Fracastoro, had not yet been fully developed, Dr Snow demonstrated a very clear understanding of it in his publications.
• While many were still following the miasma theory of disease, Dr Snow was recommending for water in London to be filtered and boiled before use in as early as 1849. Today this is known as one of the very first practical applications of germ theory.
• His main discovery came in 1854 when the third major epidemic of cholera had struck on Broad Street in Soho. By conducting a thorough investigation of the outbreak and interviewing local residents, Snow was able to identify a single public water pump on Broad Street as the source of the outbreak.
• While Dr Snow’s chemical examination of a water sample from the Broad Street pump was not able to prove its danger, he instead made a convincing enough argument by studying the disease’s pattern.
• Snow mapped the cluster of cholera cases around the pump and used statistics to demonstrate that there was a connection between the quality of the water that residents drank and their contraction of cholera.
• Snow was credited with ending the 1854 cholera outbreak, however the local council reopened the well after the epidemic subsided.

Bacteria and Louis Pasteur

• While John Snow’s achievements on germ theory occurred in medical research in England, it was a study of alcohol in neighbouring France that actually confirmed germ theory.

• The French scientist Louis Pasteur was commissioned by a French alcohol company to investigate why sugar beet, which was used in the fermentation of wine, turned sour after some time. Pasteur conducted studies and determined that the alcohol had turned due to the germs in the air that the fermenting alcohol had come into contact with.
• He proved this by sterilizing water and placing it in a swan neck flask to prevent any contact with the air.
• Pasteur was finally able to prove that it was bacteria that caused disease rather than the other way around (the so-called theory of “spontaneous generation”). After wine, he turned his research to silkworms and their health. To this day, they produce silk for the clothing industry. Louis Pasteur experimented with silkworms and discovered that they became ill when they came into contact with others who suffered from the disease.
• This way, Pasteur was able to prove that a cell’s environment had direct effects on contagion. He was thus able to begin urging hospitals to increase sterilization to control the disease.
• Pasteur conducted a whole series of formal experiments on the links between germs and diseases in 1860-1864, making discoveries that scientists still use and rely on today. He is as such seen as the father of the Germ Theory of Disease.

Virology and Dr. Robert Koch

• Building on the work of his colleagues and his own research, Robert Koch discovered exactly which bacteria caused which illnesses, including anthrax (1876), septicaemia (1878), tuberculosis (1882) and cholera (1883). He did so by discovering first how to stain and grow bacteria in a ‘Petri dish’.
• The Petri dish was named after Koch’s assistant, Julius Petri.

• Dr Robert Koch is widely known for developing the four basic criteria to demonstrate that a disease is caused by a particular organism. Koch states that:
  • The microorganism must be found in abundance in all organisms which are suffering from the disease but in organisms that are healthy.
  • The microorganism must be isolated from a diseased organism and it must be grown in pure culture.
  • This cultured microorganism should then cause disease when introduced into a healthy organism.
  • Finally, the microorganism must be again isolated from the diseased host and identified as g identical to the original specific causative agent.
• Koch’s experiments showed the idea that specific organisms could cause specific disease. His work discredited the early idea of spontaneous generation and presented the foundation for modern medical microbiology.
• His postulates became known as the Golden Era of medical bacteriology. The years between 1879 and 1889, several German microbiologists had identified organisms that caused cholera, typhoid fever, pneumonia, tetanus, diphtheria, meningitis, and gonorrhea.

Additional events/discoveries to the theory

• Invention of the microscope
  • In the 17th century, the invention of microscopes by Robert Hooke and Anton van Leeuwenhoek gave many scientists the means to observe microorganisms. This was at the same time when biologists were arguing about the concept of spontaneous generation.
• Smallpox Inoculation and Lady Montagu
  • In the early 18th century, Lady Mary Wortley Montagu, wife of the British ambassador to Constantinople wrote in her letters about how Turkish women prevented healthy people from being infected by smallpox. This preventive treatment became known as variolation in which less virulent smallpox virus was introduced to a healthy individual by scratching the arms and putting pus from an infected person.
  • After surviving smallpox herself, Lady Montagu had her children variolated and informed the English people about it. In her letters to the Royal family, Lady Montagu was able to convince the Princess of Wales to have her children variolated.
  • It is believed that the method used by the Ottomans came from Africa and Asia. In the following decades, cowpox was used by Edward Jenner (credited for developing the first vaccine against smallpox) to make healthy people immune from smallpox.
  • After the invention of microscopes which led many scientists to observe and identify microorganisms that caused diseases, the development of vaccines also aided in preventing the spread. As a result, disease transmission in both community and hospitals were reduced. More importantly, it helped many scholars to establish the germ theory.

Germ Theory Today

• With the emergence of scientific explanations regarding diseases, the Theory of the Four Humour was gone. Although people still believed in Miasma, it became less popular and was replaced by the theory of spontaneous generation. Further studies of Pasteur, Koch, and other scientists later discredited this as well.
• Spontaneous generation was the theory that microbes were the product of decaying matter, rather than the cause of its decay.
• Koch identified specific microbes that caused certain diseases
• He also proved Snow’s theory that cholera was spread through water supplies. Moreover, he discovered the bacteria causing blood poisoning, tuberculosis, and cholera in the following years.
• While Pasteur strengthened the process of pasteurization, a treatment that destroys pathogenic microorganisms in number of foods and beverages.

Image sources:

[1.] https://upload.wikimedia.org/wikipedia/commons/f/f8/Ignaz_Semmelweis_1860.jpg

[2.] https://upload.wikimedia.org/wikipedia/commons/thumb/a/a6/Louis_Pasteur%2C_foto_av_Paul_Nadar%2C_Crisco_edit.jpg/743px-Louis_Pasteur%2C_foto_av_Paul_Nadar%2C_Crisco_edit.jpg

[3.] https://upload.wikimedia.org/wikipedia/commons/5/5b/Robert_Koch_NLM.jpg