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How did people/society/scientists' view this topic change over the course of this time period? (What did they think/know at the beginning and what did they think/know at the end of this time period?)

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How did people/society/scientists' view this topic change over the course of this time period? (What did they think/know at the beginning and what did they think/know at the end of this time period?)

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The people that once believed that foul odors could create disease or that “evil spirits” could cause a person to become ill, did not take seriously that Louis Pasteur made discoveries to describe how small organisms called germs could invade the body and cause disease. Society received it as a joke since it was not one of his most important discoveries and turned into political cartoons in a comic newspaper during its time. Eventually, out of fear people started to believe it and took precaution since it was published in serious political newspapers in the 1880's.

Gabriella Izaguirre

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"The germ theory of disease states that certain diseases are caused by specific germs or infectious agents."  Louis Pasteur discovered that there were tiny living organisms in the air and these organisms can cause disease.  Pasteur conducted many different experiments that proved his theory to be correct.

Abigail Dubovetsky

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Louis Pasteur was a French chemist-turned-microbiologist, who proved the existence of microbes in air. His pioneering studies laid the foundation for the modern-day understanding of diseases, their etiology as well as vaccine development.

Did You Know?

In the fear of contracting germs, Louis Pasteur never shook hands with anybody, not even the kings and queens.

We all know that when we are down with flu, it is a set of microbes that have invaded our bodies, thereby giving rise to the symptoms. In addition to this, we are also aware that boiling water and heating food items kills the germs, and makes them safe for consumption. It isn't rocket science, is it?

But way back in the 1800s, it was not this simple. We owe our current understanding of germs or microbes to a French chemist and microbiologist called Louis Pasteur. Apart from his germ theories of fermentation and disease, we also know him as the genius who gave us the process of pasteurization.

Given below is a brief account of the germ theory of disease, as well as the significant experiments and observations of Louis Pasteur, his germ theory of fermentation and its extension to diseases.

What is 'Germ Theory of Disease'

The germ theory of disease states that certain diseases are caused by specific germs or infectious agents.

In the 1800s, this idea was not widely accepted, and it took a series of experiments and hard work for Pasteur to prove that air contains infinitely small living organisms, and that these organisms are responsible for diseases.

Such tiny living things, which we know today as microorganisms, were first observed by Antonie van Leeuwenhoek, way back in the 1670s. Moreover, the presence of microscopic, disease-carrying agents was proposed by several individuals, hundreds of years before the time of Pasteur. Observations and speculation hinting towards the presence of germs and their involvement in disease also came from the works of Fracastorius, Edward Jenner, Ignaz Semmelweis, Agostino Bassi, John Snow, and several more. But the presence of tiny invisible organisms in air was ridiculed and considered to be a fanciful story.

It was only in the 1860s that this proposition was strongly backed by evidence that came from the experiments by Louis Pasteur, followed by pioneering studies by Robert Koch and Joseph Lister. This greatly revolutionized the approach towards the study of infectious diseases as well as the treatment methods.

What paved the way for the Germ Theory of Disease?

The 1800s witnessed several studies about the generation of life, of which the spontaneous generation theory was much discussed. According to this theory, life originated spontaneously from inanimate objects. Much famous was the recipe for mice, which stated that a fully grown mice can be created from an old cloth and rotting wheat in mere 21 days. Disproving this theory was the first step towards the formulation of germ theory.

Refutation of Spontaneous Generation

The 1800s witnessed several studies about the generation of life, of which the spontaneous generation theory was much discussed. According to this theory, life originated spontaneously from inanimate objects. Much famous was the recipe for mice, which stated that a fully grown mice can be created from an old cloth and rotting wheat in mere 21 days. Disproving this theory was the first step towards the formulation of germ theory.

At this time (1860s), it was a less known fact that fermentation of beer was brought about by yeasts. In case of Louis Pasteur's vats, instead of yielding alcohol, the beetroot fermentation broth was turning sour. In order to understand what must be wrong, he took samples from these 'sick' vats and began analyzing them.

His observation of live organisms in the broth led him to investigate the spontaneous generation theory, which stated that life arises spontaneously from nonliving matter. He performed a series of experiments that involved boiling water, broths and liquid media in flasks, exposing them to air to show the presence of microorganisms in air.

One of his simplest but most significant and ingenious experiments that proved this premise has been illustrated below.

Louis Pasteur took two swan-neck flasks containing a rich liquid broth, and boiled the broths. He retained one flask as it is; and broke the neck of the other flask. The broth in the first flask remained as it is; whereas the broth in the second flask became cloudy which indicated microbial growth.

Dust particles in air entered the first flask but were stuck in the swan neck and could not travel into the broth. On the other hand, dust particles easily fell in the second flask, thereby introducing microbes into the broth. This experiment proved the existence of germs in air (dust particles in air, to be precise), and served as the final nail in the coffin of spontaneous generation theory. This experiment silenced all the debates between germ theory and spontaneous generation theory of origin of life.

Formulation of Germ Theory of Fermentation

The above experiments led him to conclude that it was the microbes in the air that spoiled the fermentation broths. He further investigated fermentation processes for several other compounds like lactic acid, butyric acid, etc. In this pursuit, he formulated the germ theory of fermentation which states that each fermentation process is associated with a specific microbe.

Louis Pasteur's Work with Diseases

Pasteur extended the germ theory of fermentation to human and animal diseases, and speculated that diseases are also the result of germs growing in the body. With this in mind, he investigated several diseases including pébrine and flacherie in silkworms, chicken cholera, anthrax in sheep, and rabies in humans. He further developed Edward Jenner's idea of vaccination, and was the first to develop and use an artificially weakened microbe as vaccine in the form of rabies vaccine. He also inspired other scientists to investigate diseases using this approach, and the rest is history.

The papers submitted by Louis Pasteur and Robert Koch regarding their observations and therapeutic suggestion with respect to anthrax, constitute the first formal representations of the germ theory of diseases. But Pasteur's most significant contribution came from his experiments on germs, which permanently ended the debate with spontaneous generation. While demonstrating that boiled water can remain sterile until it is exposed to air, he said:
"Life is germ and a germ is life. Never will the doctrine of spontaneous generation recover from the mortal blow of this simple experiment."
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A Brief Summary of Louis Pasteur's Germ Theory of Disease

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Louis Pasteur was a French chemist-turned-microbiologist, who proved the existence of microbes in air. His pioneering studies laid the foundation for the modern-day understanding of diseases, their etiology as well as vaccine development. In the fear of contracting germs, Louis Pasteur never shook hands with anybody, not even the kings and queens.

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What evidence surfaced during this time related to the topic?

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What evidence surfaced during this time related to the topic?

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During this time period, Louis Pasteur's experiment and evidence or pasteurization proved that bacteria can still grow even when the object seems to appear "clean." In addition, he proved that when things interact with the air and are unsealed they can grow germs and bacteria that can lead to diseases.  The idea of if something appears clean or is washed or boiled does not mean it does not contain germs and/or bacteria. In addition, during this time period people learned that even though a certain object or substance is boiled and is "rid of germs" does not mean those germs cannot grow back. In this time period the public discovered that germs and bacteria can cause diseases.

Sophia Romano

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What is one aspect of this time period that would be useful to include if you were teaching your elementary students about this topic?

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What is one aspect of this time period that would be useful to include if you were teaching your elementary students about this topic?

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One aspect that would be useful for teaching  elementary students is that even though something looks clean, it does not mean it does not contain germs or bacteria. A teacher could teach this by explaining to their students how important it is to wash their hands. There are germs and bacteria on our hands and even though they do not appear dirty they still need to be washed to help get rid of the growing germs and bacteria. During this time period, people did not think about bacteria and/or diseases coming from unpreserved food for example.

Sophia Romano

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What changes were made to what we (society; people) believed to be true?

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What changes were made to what we (society; people) believed to be true?

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- The biggest thing that we, the people as a society, came to learn was that bacteria causes diseases. People thought many different things, such as you obtained a disease as a punishment due to one's evil behavior,  foul odors, or even poisonous vapors. Once we came to research and prove that bacteria is what causes diseases, these things that people had believed, changed.

Taylor Clivio

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The germ theory is a fundamental tenet of medicine that states that microorganisms, which are too small to be seen without the aid of a microscope, can invade the body and cause certain diseases.

Until the acceptance of the germ theory, many people believed that was punishment for a person's evil . When entire populations fell ill, the disease was often blamed on swamp vapors or foul odors from sewage. Even many educated individuals, such as the prominent seventeenth century English physician William Harvey, believed that epidemics were caused by miasmas, poisonous vapors created by planetary movements affecting the , or by disturbances within the Earth itself.

The development of the germ theory was made possible by the certain laboratory tools and techniques that permitted the study of bacteria during the seventeenth and eighteenth centuries.

The invention of primitive microscopes by the English scientist Robert Hooke and the Dutch merchant and amateur scientist Anton van Leeuwenhoek in the seventeenth century, gave scientists the means to observe microorganisms. During this period a debate raged among biologists regarding the concept of spontaneous generation.

Until the second part of the nineteenth century, many educated people believed that some lower life forms could arise spontaneously from nonliving , for example, from manure and maggots from decaying corpses. In 1668, however, the Italian physician Francisco Redi demonstrated that decaying meat in a container covered with a fine net did not produce maggots. Redi asserted this was proof that merely keeping egg-laying flies from the meat by covering it with a net while permitting the passage of air into the containers was enough to prevent the appearance of maggots. However, the belief in spontaneous generation remained widespread even in the scientific community.

In the 1700s, more evidence that microorganisms can cause certain diseases was passed over by physicians, who did not make the connection between vaccination and microorganisms. During the early part of the eighteenth century, Lady Montague, wife of the British ambassador to that country, noticed that the women of Constantinople routinely practiced a form of prevention that included "treating" healthy people with pus from individuals suffering from smallpox. Lady Montague noticed that the Turkish women removed pus from the lesions of smallpox victims and inserted a tiny bit of it into the of recipients.

While the practice generally caused a mild form of the illness, many of these same people remained healthy while others succumbed to smallpox epidemics. The reasons for the success of this preventive treatment, called variolation, were not understood at the , and depended on the coincidental use of a less virulent smallpox and the fact that the virus was introduced through the skin, rather than through its usually route of entry-the respiratory tract.

Lady Montague introduced the practice of variolation to England, where physician Edward Jenner later modified and improved the technique of variolation. Jenner noticed that milkmaids who contracted cowpox on their hands from touching the lesions on the udders of cows with the disease rarely got smallpox. He showed that inoculating people with cowpox can prevent smallpox. The success of this technique, which demonstrated that the identical substance need not be used to stimulate the body's protective mechanisms, still did not convince many educated people of the existence of disease-causing microorganisms.

Thus, the debate continued well into the 1800s. In 1848, Ignaz P. Semmelweis, a Hungarian physician working in German hospitals, discovered that a sometimes fatal commonly found in maternity hospitals in could be prevented by simple hygiene. Semmelweis demonstrated that medical students doing autopsies on the bodies of women who died from puerperal fever often spread that disease to maternity patients they subsequently examined. He ordered these students to wash their hands in chlorinated lime before examining pregnant women. Although the of puerperal fever in his hospital plummeted dramatically, many other physicians continued to criticize this practice as being useless.

In 1854, modern epidemiology was born when the English physician John Snow determined that the source of cholera epidemic in London was the contaminated water of the Broad Street pump. After he ordered the pump closed, the epidemic ebbed. Nevertheless, many physicians refused to believe that invisible organisms could spread disease.

The argument took an important turn in 1857, however, when the French chemist Louis Pasteur discovered "diseases" of wine and beer. French brewers asked Pasteur to determine why wine and beer sometimes spoiled. Pasteur showed that, while yeasts produce from the sugar in the brew, bacteria can change the alcohol to vinegar. His suggestion that brewers their product enough to kill bacteria but not , was a boon to the industry-a process called pasteurization. In addition, the connection Pasteur made between food spoilage and microorganisms was a key step in demonstrating the link between microorganisms and disease. Indeed, Pasteur observed that, "There are similarities between the diseases of animals or man and the diseases of beer and wine." The notion of spontaneous generation received another blow in 1858, when the German scientist Rudolf Virchow introduced the concept of biogenesis. This concept holds that living cells can arise only from preexisting living cells. This was followed in 1861 by Pasteur's demonstration that microorganisms present in the air can contaminate solutions that seemed sterile. For example, boiled nutrient media left uncovered will become contaminated with microorganisms, thus disproving the notion that air itself can create microbes.

In his classic experiments, Pasteur first filled short-necked flasks with beef broth and boiled them. He left some opened to the air to cool and sealed others. The sealed flasks remained free of microorganisms, while the open flasks were contaminated within a few days. Pasteur next placed broth in flasks that had open-ended, long necks. After bending the necks of the flasks into S-shaped curves that bent downward, then swept sharply upward, he boiled the contents. Even months after cooling, the uncapped flasks remained uncontaminated. Pasteur explained that the S-shaped curve allowed air to pass into the flask; however, the curved neck trapped airborne microorganisms before they could contaminate the broth.

Pasteur's work followed earlier demonstrations by both himself and Agostino Bassi, an amateur microscopist, that silkworm diseases can be caused by microorganisms. While these observations in the 1830s linked the activity of microorganisms to disease, it was not until 1876 the German physician Robert Koch proved that bacteria can cause diseases. Koch showed that the bacterium Bacillus anthracis was the cause of in cattle and , and he discovered the that causes tuberculosis.

Koch's systematic methodology in proving the cause of anthrax was generalized into a specific set of guidelines for determining the cause of infectious diseases, now known as Koch's postulates. Thus, the following steps are generally used to obtain proof that a particular organism causes a particular disease:

1. The organism must be present in every case of the disease.

2. The organism must be isolated from a host with the corresponding disease and grown in pure culture.

3. Samples of the organism removed from the pure culture must cause the corresponding disease when inoculated into a healthy, susceptible laboratory animal.

4. The organism must be isolated from the inoculated animal and identified as being identical to the original organisms isolated from the initial, diseased host.

By showing how specific organisms can be identified as the cause of specific diseases, Koch helped to destroy the notion of spontaneous generation, and laid the foundation for modern medical microbiology.

Koch's postulates introduced what has been called the "Golden Era" of medical bacteriology. Between 1879 and 1889, German microbiologists isolated the organisms that cause cholera, typhoid fever, diphtheria, , , meningitis, gonorrhea, as well the staphylococcus and streptococcus organisms.

Even as Koch's work was influencing the development of the germ theory, the influence of the English physician Joseph Lister was being felt in operating rooms. Building on the work of both Semmelweis and Pasteur, Lister began soaking surgical dressings in carbolic acid (phenol) to prevent postoperative infection. Other surgeons adopted this practice, which was one of the earliest attempts to control infectious microorganisms.

Thus, following the invention of microscopes, early scientists struggled to show that microbes can cause disease in humans, and that public health measures, such as closing down sources of contamination and giving healthy people vaccines, can prevent the spread of disease. This led to reduction of disease transmission in hospitals and the community, and the development of techniques to identify the organisms that for many years were considered to exist only in the imaginations of those researchers and physicians struggling to establish the germ theory.

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The germ theory is a fundamental tenet of medicine that states that microorganisms , which are too small to be seen without the aid of a microscope , can invade the body and cause certain diseases. Until the acceptance of the germ theory, many people believed that was punishment for a person's evil .

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1. What vaccinations can medical professionals create with this knowledge?
2. How can we use this theory to help save those who contract the diseases through germs?
3. Does anyone have immunity to germs based on this theory?

Megan Flowers

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Pasteur's Test of Spontaneous Generation 

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Pasteur's Test of Spontaneous Generation 

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 Timeline of major developments of the Germ Theory

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 Timeline of major developments of the Germ Theory

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1861- Louis Pasteur publishes the Germ Theory after experimentation and proves that bacteria causes diseases.

1861-Pasteur demonstrates that microorganisms present in the air can contaminate solutions that appear germ-free.

1862-Pasteur disproved spontaneous generation which is the theory that living organisms develop from nonliving matter.

1862- Pasteur invented a process where bacteria could be removed from liquid by heating and then cooling it.  This process is known as pasteurization.

1863-Casimir Joseph Davaine reported the transmission of anthrax by the injection of healthy sheep with the blood of animals dying of the disease and the finding of microscopic rod-shaped bodies in the blood of both groups of sheep.  However, Davaine did not know about the spores of bacteria that could cause anthrax

1864- Pasteur went on to study where the bacteria growing in food and drinks were coming from, and he finally figured out it came from the air or environment.

1875-1876- Robert Koch hypothesized that spores, without the bacteria present, could cause anthrax

1876- Robert Koch proves that bacteria can cause diseases.

1876-Robert Koch  discovered and invented agar, and that different kinds of microbes cause different kinds of diseases.

Abigail Dubovetsky