Origin of Everything


How We Discovered Germs

Humanity didn't always know about the invisible viruses, bacteria, and microbes that can cause disease. But that doesn't mean we didn't come up with some truly bizarre ideas. From the four humors and miasma theory to bloodletting and trepanation, Danielle traces humanity's winding road to the Germ Theory of Disease that revolutionized the medical profession.

AIRED: May 29, 2020 | 0:09:07

Germs. We’re all familiar with the little creepy crawlies that are invisible to the

naked eye but can make us really sick. But humanity didn’t always know about these

tiny microbes, viruses and bacteria (commonly all grouped together as pathogens).

So what was the path to discovery that led us to realizing that tiny specimen even existed?

And what did we believe before and after the germ theory of disease was considered the


Well today on Origin of Everything we’re going to take a stroll down memory (or history)

lane to look back on all the twists and turns that led to the first germ discoveries of

the 19th and 20th centuries and how these new revelations revolutionized the medical profession.

So what were some of the working theories of disease before we knew what (actually)

makes us sick? Well hang on to your hats because some of these theories are going to sound

positively medieval... or ancient historical at the very least.

NPR’s “Goats and Soda” does an interesting job of tracing the history of humans and disease.

In short they note that early humans lived in forager and hunter societies where they

were migrating and living further apart. As a result though they were often exposed to

disease from interacting with the animals that they hunted for food, it was harder for

these diseases to spread from human to human.

But with the rise of the domestication of animals and agriculture, humans began to settle

down in fixed locations for long periods of time. This led to the development of towns

and cities where diseases could spread from person to person more rapidly.

But rather than deducing that living in close proximity to wild animals and other dirty

humans may not be such a hot thing, they attributed it to the rise of bad air.

One of the oldest and most commonly held beliefs about the spread of disease was a practice

known as “miasma theory.” Miasma theory stated that disease was spread by miasmas,

an outdated word that essentially means “bad air” or night air.

Miasmas were thought to emanate from foul smelling and unsanitary living conditions

like human waste (yuck), dirty water and rotting food. The thought went that these gross conditions

gave rise to miasmas that went on to cause major illnesses like cholera, malaria and

the plague (aka Black Death). And although this “bad air” belief may seem odd to

us today, it had a strangely long staying power.

The roots of miasma theory date back to Ancient Greece, China and Rome and continued to be

the prevalent theory of disease until the mid 19th century. That’s literally hundreds

of years believing that disease most likely came from one place.

We now know that things like unclean water, interacting with human waste and unsanitary

living conditions can contribute to disease, but we also know it’s not from big clouds

of bad air roaming through the streets.

However there is historical evidence that other schools of thought existed. And these

ranged from blaming illness on witchcraft to exposure to demons and devils. Some also

posit that certain religious rituals and rites (like hand washing) may have shown an early

understanding of how illness spreads.

But those theories were less about disease and science and stemmed more from personally

and culturally held views. Battling disease prior to the germ theory of disease’s emergence

in the 19th century was also equally misguided. People resorted to drilling holes in peoples

heads, bloodletting and leeching, arsenic, incantations, and a host of balms and salves

that could work...but could also ultimately kill a person faster than the pathogens would.

But big changes came on the scene in the mid 19th century.

Scientists were having doubts regarding the not-totally-logical theories about disease

spread, so they did what all good scientists do: they conducted experiments. Three important

experimenters helped develop germ theory.

The first was French scientist Louis Pasteur who in the mid-1800s demonstrated how yeast

could cause fermentation. This led to the invention of pasteurization, as you all know

from your middle school science classes, but it also led to an understanding that fermentation

was a biological process involving living organisms.

The second was one of Pasteur's contemporaries, German physician Robert Koch, who believed

that a microscopic organism was responsible for anthrax. After much research, he saw the

microbe Bacillus anthracis with his microscope, proving that a germ could cause a disease.

The third important contributor to germ theory was British physician Joseph Lister who read

Pasteur's research and conducted an experiment of his own: disinfecting bandages, medical

instruments, and spaces where patients were seen. He also began washing his hands.

These methods of course helped to keep patients healthier and other doctors and researchers

took note. By the way if you're interested in more about the history of hand washing,

we have a video on that right here on our channel.

It’d be impossible to overstate the importance of the work of Pasteur, Koch, Lister and their

contemporaries to the medical field. The understanding that germs -- primarily bacteria, viruses,

fungi, and protozoa -- are responsible for the spread of many diseases led to a massive

acceleration in researchers identifying specific disease causes, preventers, and treatments.

And like the researchers before them, this new wave of scientists found inspiration in

each other’s work.

One scientist who piggybacked off of their findings was a physician named Patrick Manson.

In 1878 he demonstrated for the first time that insects can host germ-carrying parasites

that cause diseases in humans.

His research then inspired a colleague, doctor Ronald Ross who, discovered that mosquitoes

were the ones spreading malaria to humans. These were hugely important findings. Now

that people understood that they could get sick from insects, it was possible to mitigate

epidemics of those diseases and start to work on cures.

Another disease that was causing major issues at the time was syphilis. Syphilis had emerged

in deadly outbreaks in Europe since at least the 1490s. Famous philosopher Erasmus once

called it “the most destructive of all diseases.”

In the early 20th century, two researchers, Paul Ehrlich and Sahachiro Hata, tested more

than 900 chemical compounds on mice before they made their discovery: compound #606 could

kill the microbe responsible for syphilis. This led to the release of the drug Salvarsan.

One of the researchers who immediately began giving Salvarsan to patients by inserting

it into their veins, a rare way of administering medicine at the time, was physician Alexander

Fleming. That’s right: the invention of Salvarsan led to Fleming’s greatest discovery:

penicillin in 1928. Being able to kill bacteria with antibiotics changed the world.

During the early 1900s, pneumonia had a reported 30-40% fatality rate; in a 2010 analysis of

over one million elderly patients hospitalized in the US with pneumonia, the mortality rate

was 11% within 30 days of admission. And that’s just one example of the positive consequences.

People could now take penicillin for a wide range of bacterial infections, but one of

the disease-causing germs remained more mysterious: the virus. Which is perhaps surprising considering

molecular genetic researcher Lotti Tajouri has put it: “Viruses are the most common

biological entities on Earth.”

They’re literally everywhere, including the one we’re facing now: SARS-CoV-2, the

virus behind COVID-19. But viruses are smaller than bacteria and protozoa so it wasn’t

until the early 1940s that we got clear photographs of them.

Most early discoveries regarding viruses actually came from botanists trying to better comprehend

a virus that was going after tobacco plants. The word “virus” was coined by a microbiologist

studying that phenomenon, who named it after the Latin term for venom.

Though there were a few vaccines for viruses before the 20th century, that’s the century

that virus vaccines exploded. Influenza got an effective vaccine in the 1940s.

One of the men responsible for its creation, physician and researcher Jonas Salk, went

on to announce that he’d created a polio vaccine in 1953, a year after a polio epidemic

in which 58,000 new diagnoses were reported in the US.

A measles vaccine was released in 1963. Up until that time 48,000 Americans had been

hospitalized with measles every year. In 1964, there was a rubella epidemic in which 12.5

million Americans contracted the disease. That same year physician and researcher Stanley

Plotkin developed the rubella vaccine. It was a golden age.

In 1972 the Natural History of Infectious Disease textbook boldly claimed: “The most

likely forecast about the future of infectious disease is that it will be very dull. There

may be some wholly unexpected emergence of a new and dangerous infectious disease, but

nothing of the sort has marked the last fifty years.” And indeed humanity would continue

to face pandemics, including the AIDS pandemic as well as one that we’re facing now, the

COVID-19 pandemic.

Even though we continue to face new challenges, , we can look back with hope on all of this

progress. Scientists figured out the genetic sequence of COVID-19 and just 63 days later,

vaccines were being tested on people.

Director of the National Institute of Allergy and Infectious Diseases Anthony Fauci called

that “record pace.” None other than 87-year-old Stanley Plotkin, the inventor of the rubella

vaccine, is currently consulting for six companies that are working on coronavirus vaccines.

So we continue to see the benefits of collective learning dating all the way back to the original

conceivers of germ theory. And who knows what problems this data we’re collecting now

will help to solve in the future.


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