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Germ Theory and Scientists

Germ Theory

Vibrio cholerae causes cholera infection.

Germ Theory is the scientific idea that many diseases are caused by tiny organisms called germs, such as bacteria and viruses.

Germs can enter the body through the air, food, water, or contact with other people. Once inside the body, they can multiply and make a person sick.

Germ theory explains why handwashing, clean water, vaccines, and medicines help prevent and treat diseases.

In science, a theory is a well-tested explanation for how something works. Germ theory explains how microorganisms cause disease.

It took scientists hundreds of years to understand this. Germ theory replaced miasma theory. Germ theory the foundation of modern medicine.

Bacteria are free-living cells that can live inside or outside a body. Viruses are considered non-living by many scientists because they cannot reproduce on their own.

Obsolete Theories

Over the many years, people entertained many unusual theories including miasma theory and spontaneous generation. Miasma theory stated that disease was caused by noxious gas or night air. Miasma was thought to come from rotting matter. Spontaneous generation is discussed below.

Both miasma theory and spontaneous generation have been disproven.

An 1831 color lithograph by Robert Seymour depicts cholera as a robed, skeletal creature emanating a deadly black cloud.

Spontaneous Generation

Spontaneous Generation was a misguided belief that held that life came from nonliving matter. For instance, rats were thought to come from garbage. Mushrooms were thought to come from dead logs. Fleas arose from dust. No parents were thought necessary to bring about new life.

Aristotle (384 - 322 BC) supported spontaneous generation theory. Aristotle believed that "vital heat" was required for Spontaneous Generation to happen.

Spontaneous Generation was taken as scientific fact for 2000 years!

Jan Baptist van Helmont

He is remembered today for his ideas concerning spontaneous generation. He had a theory that mice come about from rags and wheat. He was not correct. (Baby mice come from mommy mice.)

Although Van Helmont was wrong about spontaneous generation, he did contribute to science. He coined the term "gas."

Perhaps his most famous experiment showed that tree mass can be attributed to water, not soil.

People believed in spontaneous generation for roughly two thousand years, since Aristotle first proposed it.

Finally, in 1862, Louis Pasteur proved spontaneous generation to be wrong with his famous swan neck flask experiment.

Some People Who Helped Develop Germ Theory

Listed below are some of the important people who helped mankind understand why and how people get sick.

Robert Hooke - 1665

Robert Hooke embraced and improved the first microscopes by designing his own light microscope.

Hooke observed cork cells and coined the term cell for describing biological organisms. The term was suggested by the resemblance of plant cells to monks' cells.

Robert Hooke was an excellent illustrator and he published his findings in a book called Micrographia. His work led to cell theory.

Robert Hooke saw cells first. He called them cells.

This picture shows Robert Hooke's microscope and what he saw.

Francesco Redi - 1668

In 1668, Francesco Redi was the founder of experimental biology. He showed that maggots came from adult flies. Maggots did not spontaneously generate from rotting meat. Unfortunately, although this experiment was pretty clear, scientists continued to debate spontaneous generation for another 200 years.

Francesco Redi

Red's experiment showed that maggots come from fly eggs. If flies cannot lay eggs on the meat, there will be no maggots.

Antonie Phillips van Leeuwenhoek - 1674

Microbes were first discovered by an amateur Dutch scientist named Antonie Phillips van Leeuwenhoek in the 1670s. He was a pioneer in microscopy. In fact, he was the first person to see microscopic life! He was the first to document muscle fibers, red blood cells, sperm cells, and bacteria. He was the father of microbiology.

Animicules = Protists

Dr. Edward Jenner - 1796

In 1796, Dr. Edward Jenner used Vaccinia (cowpox) to vaccinate against smallpox. He observed that milkmaids often suffered from cowpox but rarely suffered from smallpox. It occurred to him that cowpox prevented milkmaids from catching smallpox. Dr. Jenner inoculated a 13 year-old-boy with "vaccinia virus", which was known as cowpox. The boy was immune to smallpox. This was the first vaccine.

Smallpox virus, a stable DNA virus, is no longer found in the wild. However, it is reportedly held in a freezer at the CDC.

Latin word: vacca = cow. The word vaccine comes from vacca, meaning cow. Vaccinia is related to cowpox and was used to protect against smallpox.

On May 14, 1796, Dr. Edward Jenner used matter from a cowpox lesions to inoculate an 8-year-old boy, James Phipps.

Ignaz Semmelweis - 1847

Semmelweis faced strong opposition from other doctors, and his ideas were largely ignored during his lifetime.

1847 - Ignaz Semmelweis proved that hand washing prevented the spread of childbirth fever. Handwashing stops the spread of disease.

Childbirth fever was caused by bacteria entering the uterus.

Prior to this discovery, many doctors were responsible for infecting many of their patients. Oops.

Dr. John Snow - 1854

Cholera is a horrific diarrheal illness caused by Vibrio cholerae bacteria. This bacteria infects intestines. Cholera used to kill 50% of the people who got it.

In the 1800s, people believed that cholera was transmitted by "Miasma", a poisonous cloud. They did not believe in germ theory.

It was Robert Koch who discovered cholera bacillus, Vibrio cholerae in the year 1884.

In August 1854, a cholera outbreak occurred in Soho. Dr. John Snow proved that cholera was caused by drinking water that was tainted with human waste.

Dr. Snow collected death data and plotted cases of cholera on a map. Dr. Snow determined that the Broad Street pump was the site of infection.

Dr. Snow was the first doctor to trace cholera. He was our first epidemiologist. His peers at the time did not appreciate his efforts.

It wasn't until 1884 that Robert Koch discovered cholera bacillus, Vibrio cholerae.

Copy of Caroline and Claire

Louis Pasteur Proves Spontaneous Generation is False - 1862

Pasteur was a French chemist and microbiologist who finally put the spontaneous generation issue to rest in 1862.

Pasteur proved that spontaneous generation was not true with his elegant swan neck experiment that allowed air to enter the flask while trapping microbes. The broth remained sterile.

Pasteur showed that air alone does not support growth. Further, he showed that the broth could support growth once microbes were introduced.

Microbial growth comes from microbes - not the broth itself.

Before Pasteur, people thought that diseases just appeared. Louis Pasteur showed that invisible germs caused sickness and spoilage. Pasteur was very important in the development of germ theory.

Louis Pasteur in his lab.

Pasteur's Swan Neck Flask

Life comes from life

Louis Pasteur showed (with swan neck flasks) that microorganisms only came from other microorganisms and that a sterile broth would remain so -unless contaminated by life.

Life comes from preexisting life. Omne vivum ex vivo!

Louis Pasteur Invents Pasteurization - 1863

Louis Pasteur also showed that heating food would kill microbes that would make the food go bad. This process is now called Pasteurization. Pasteurization is used to treat milk and other foods.

Louis Pasteur

Pasteur's Disease Discoveries

From 1877 to 1887, Pasteur employed these fundamentals of microbiology in the battle against infectious diseases.

Pasteur and other scientists helped identify several disease-causing bacteria, including staphylococcus, streptococcus, and pneumococcus.

"Coccus" indicates that the bacteria are round.

Pasteur's Vaccines

Louis Pasteur discovered the method of weakening virulent microorganisms. His method is the basis of vaccination.

Vaccines contain a weak or dead germ. Sometimes vaccines contain only the proteins of germs. Vaccines are safe ways to teach your immune system how to fight off the real germ.

Louis Pasteur developed vaccines against chicken cholera, anthrax, and swine erysipelas.

Rabies Vaccine -1885

After mastering his method of vaccination, Louis Pasteur applied this concept to rabies. On July 6, 1885, Pasteur tested his pioneering rabies treatment on man for the first time: the young Joseph Meister was saved.

Rabies

Joseph Lister Uses Antiseptics - 1865

1865 - Joseph Lister proved that chemicals –specifically phenol (a.k.a., carbolic acid) - can be used to prevent infection. An antiseptic is a chemical that prevents infection.

Carbolic acid sprays on the open wound during surgery. The chemical kills germs.

Robert Koch - Proves Germs Cause Disease! Nobel Prize Winner (1905)

Robert Koch

In 1882, Robert Koch discovered tubercle bacillus that caused tuberculosis. Before Koch, people didn't really know what caused diseases like "consumption" (tuberculosis). Koch proved that tiny, invisible bacteria were the culprits, not bad air or curses. He proved that germs caused disease.
Koch was like a detective, finding the specific bacteria responsible for diseases like tuberculosis (the "consumption" germ) and cholera.
Koch's Postulates (His "Rulebook"): Koch created a simple set of rules (postulates) to prove a microbe causes a disease:

1. 1. Find the germ in sick animals.
  2. Grow it in a lab.
  3. Put it in a healthy animal, and it gets sick.
  4. Take the germ out of the new sick animal, and it's the same one.

Founder of Bacteriology: His work made bacteriology (the study of bacteria) a real science, helping us understand and prevent infections.

He also discovered cholera bacillus, Vibrio cholerae in the year 1884.

1890 – Robert Koch created experimental steps for directly relating a specific microbe to a specific disease:

1. Germ must be found in all sick animals, but not in healthy animals. a

2. Germ must be grown in culture.

3. Cultured germ should make healthy animals sick. b

4. Germ must be found in sick animal.

a. Sometimes healthy animals are carriers. (cholera and typhoid)

b TB, cholera and HIV-infection don’t always result in sickness

In the late 1800s, Louis Pasteur and Robert Koch helped develop the science of bacteriology when they discovered a link between bacteria, fermentation, and disease.

Koch and Pasteur independently provided experimental evidence anthrax was caused by anthrax bacillus. Their work established the germ theory of disease.

Sir Alexander Fleming Discovers Penicillin - Nobel Prize Winner (1945)

In 1928, Alexander Fleming discovered penicillin by accident. Penicillin is an antibiotic, which is used to treat bacterial infections.

Howard Walter Florey discovered Alexander Fleming's work on penicillin about 10 years later. He purified the active ingredients, tested the antibiotic on mice, and saw that it worked.

Antibiotics greatly reduced deaths from infection during World War II. Alexander Fleming was awarded the Nobel Prize for physiology or medicine in 1945 for work on penicillin.

Jonas Salk - Creates Polio Vaccine

In 1955, Jonas Salk made the Polio vaccine. He successfully disabled the virus so that it could not infect humans. The virus still had recognizable antigens.

Poliovirus attacks the coating of nerve cells. Paralysis is often the result.

Polio Virus

Victims

Iron Lung

How Germ Theory Changed the World:

Germ theory helped scientists and doctors understand that germs cause disease. Because of this, people learned how to prevent the spread of illness.

Handwashing and sanitation help remove germs from our hands and communities.

Clean water and food safety prevent germs from entering our bodies through drinking water or meals.

Hospitals and surgery became much safer when doctors used antiseptics and followed strict hygiene practices. Together, these practices save millions of lives and keep people healthy every day.

Random Practice Questions about Germ Theory

New England Vampire Folk Belief: The Archaeological Evidence" by Nick Bellantoni

Vampires in Exeter? The Gruesome Tale of Mercy L. and Edwin A. Brown

Try and infect the world!

Germ Theory Vocabulary

Antibiotic -An antibiotic is a medicine used to kill bacteria or stop them from growing. Antibiotics do not work against viruses.

Antigen - An antigen is a substance on a germ that triggers the immune system to make antibodies to fight the infection.

Antiseptic - An antiseptic is a chemical used on living tissue (like skin) to kill germs and prevent infection.

Carrier - A carrier is a person who has a pathogen in their body but does not feel sick. Carriers can still spread the disease to others.

Epidemiologist - An epidemiologist is a scientist who studies how diseases spread and works to control outbreaks.

Pathogen - A pathogen is a germ that causes disease. Examples include bacteria, viruses, fungi, and parasites.

Sanitation means keeping things clean to prevent the spread of germs and disease. This includes safe trash disposal, clean bathrooms, sewage systems, and washing hands and surfaces regularly.

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