pasteur's experiment explained

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Pasteur's Experiment

The steps of Pasteur's experiment are outlined below:

First, Pasteur prepared a nutrient broth similar to the broth one would use in soup.

Next, he placed equal amounts of the broth into two long-necked flasks. He left one flask with a straight neck. The other he bent to form an "S" shape.

Then he boiled the broth in each flask to kill any living matter in the liquid. The sterile broths were then left to sit, at room temperature and exposed to the air, in their open-mouthed flasks.

After several weeks, Pasteur observed that the broth in the straight-neck flask was discolored and cloudy, while the broth in the curved-neck flask had not changed.

He concluded that germs in the air were able to fall unobstructed down the straight-necked flask and contaminate the broth. The other flask, however, trapped germs in its curved neck, preventing them from reaching the broth, which never changed color or became cloudy.

If spontaneous generation had been a real phenomenon, Pasteur argued, the broth in the curved-neck flask would have eventually become reinfected because the germs would have spontaneously generated. But the curved-neck flask never became infected, indicating that the germs could only come from other germs.

Pasteur's experiment has all of the hallmarks of modern scientific inquiry. It begins with a hypothesis and it tests that hypothesis using a carefully controlled experiment. This same process — based on the same logical sequence of steps — has been employed by scientists for nearly 150 years. Over time, these steps have evolved into an idealized methodology that we now know as the scientific method. After several weeks, Pasteur observed that the broth in the straight-neck flask was discolored and cloudy, while the broth in the curved-neck flask had not changed.

Let's look more closely at these steps.

Please copy/paste the following text to properly cite this HowStuffWorks.com article:

3.1 Spontaneous Generation

Learning objectives.

By the end of this section, you will be able to:

Explain the theory of spontaneous generation and why people once accepted it as an explanation for the existence of certain types of organisms
Explain how certain individuals (van Helmont, Redi, Needham, Spallanzani, and Pasteur) tried to prove or disprove spontaneous generation

Clinical Focus

Barbara is a 19-year-old college student living in the dormitory. In January, she came down with a sore throat, headache, mild fever, chills, and a violent but unproductive (i.e., no mucus) cough. To treat these symptoms, Barbara began taking an over-the-counter cold medication, which did not seem to work. In fact, over the next few days, while some of Barbara’s symptoms began to resolve, her cough and fever persisted, and she felt very tired and weak.

What types of respiratory disease may be responsible?

Jump to the next Clinical Focus box

Humans have been asking for millennia: Where does new life come from? Religion, philosophy, and science have all wrestled with this question. One of the oldest explanations was the theory of spontaneous generation, which can be traced back to the ancient Greeks and was widely accepted through the Middle Ages.

The Theory of Spontaneous Generation

The Greek philosopher Aristotle (384–322 BC) was one of the earliest recorded scholars to articulate the theory of spontaneous generation , the notion that life can arise from nonliving matter. Aristotle proposed that life arose from nonliving material if the material contained pneuma (“spirit” or “breath”). As evidence, he noted several instances of the appearance of animals from environments previously devoid of such animals, such as the seemingly sudden appearance of fish in a new puddle of water. 1

This theory persisted into the 17th century, when scientists undertook additional experimentation to support or disprove it. By this time, the proponents of the theory cited how frogs simply seem to appear along the muddy banks of the Nile River in Egypt during the annual flooding. Others observed that mice simply appeared among grain stored in barns with thatched roofs. When the roof leaked and the grain molded, mice appeared. Jan Baptista van Helmont , a 17th century Flemish scientist, proposed that mice could arise from rags and wheat kernels left in an open container for 3 weeks. In reality, such habitats provided ideal food sources and shelter for mouse populations to flourish.

However, one of van Helmont’s contemporaries, Italian physician Francesco Redi (1626–1697), performed an experiment in 1668 that was one of the first to refute the idea that maggots (the larvae of flies) spontaneously generate on meat left out in the open air. He predicted that preventing flies from having direct contact with the meat would also prevent the appearance of maggots. Redi left meat in each of six containers ( Figure 3.2 ). Two were open to the air, two were covered with gauze, and two were tightly sealed. His hypothesis was supported when maggots developed in the uncovered jars, but no maggots appeared in either the gauze-covered or the tightly sealed jars. He concluded that maggots could only form when flies were allowed to lay eggs in the meat, and that the maggots were the offspring of flies, not the product of spontaneous generation.

In 1745, John Needham (1713–1781) published a report of his own experiments, in which he briefly boiled broth infused with plant or animal matter, hoping to kill all preexisting microbes. 2 He then sealed the flasks. After a few days, Needham observed that the broth had become cloudy and a single drop contained numerous microscopic creatures. He argued that the new microbes must have arisen spontaneously. In reality, however, he likely did not boil the broth enough to kill all preexisting microbes.

Lazzaro Spallanzani (1729–1799) did not agree with Needham’s conclusions, however, and performed hundreds of carefully executed experiments using heated broth. 3 As in Needham’s experiment, broth in sealed jars and unsealed jars was infused with plant and animal matter. Spallanzani’s results contradicted the findings of Needham: Heated but sealed flasks remained clear, without any signs of spontaneous growth, unless the flasks were subsequently opened to the air. This suggested that microbes were introduced into these flasks from the air. In response to Spallanzani’s findings, Needham argued that life originates from a “life force” that was destroyed during Spallanzani’s extended boiling. Any subsequent sealing of the flasks then prevented new life force from entering and causing spontaneous generation ( Figure 3.3 ).

Check Your Understanding

Describe the theory of spontaneous generation and some of the arguments used to support it.
Explain how the experiments of Redi and Spallanzani challenged the theory of spontaneous generation.

Disproving Spontaneous Generation

The debate over spontaneous generation continued well into the 19th century, with scientists serving as proponents of both sides. To settle the debate, the Paris Academy of Sciences offered a prize for resolution of the problem. Louis Pasteur , a prominent French chemist who had been studying microbial fermentation and the causes of wine spoilage, accepted the challenge. In 1858, Pasteur filtered air through a gun-cotton filter and, upon microscopic examination of the cotton, found it full of microorganisms, suggesting that the exposure of a broth to air was not introducing a “life force” to the broth but rather airborne microorganisms.

Later, Pasteur made a series of flasks with long, twisted necks (“swan-neck” flasks), in which he boiled broth to sterilize it ( Figure 3.4 ). His design allowed air inside the flasks to be exchanged with air from the outside, but prevented the introduction of any airborne microorganisms, which would get caught in the twists and bends of the flasks’ necks. If a life force besides the airborne microorganisms were responsible for microbial growth within the sterilized flasks, it would have access to the broth, whereas the microorganisms would not. He correctly predicted that sterilized broth in his swan-neck flasks would remain sterile as long as the swan necks remained intact. However, should the necks be broken, microorganisms would be introduced, contaminating the flasks and allowing microbial growth within the broth.

Pasteur’s set of experiments irrefutably disproved the theory of spontaneous generation and earned him the prestigious Alhumbert Prize from the Paris Academy of Sciences in 1862. In a subsequent lecture in 1864, Pasteur articulated “ Omne vivum ex vivo ” (“Life only comes from life”). In this lecture, Pasteur recounted his famous swan-neck flask experiment, stating that “…life is a germ and a germ is life. Never will the doctrine of spontaneous generation recover from the mortal blow of this simple experiment.” 4 To Pasteur’s credit, it never has.

How did Pasteur’s experimental design allow air, but not microbes, to enter, and why was this important?
What was the control group in Pasteur’s experiment and what did it show?
1 K. Zwier. “Aristotle on Spontaneous Generation.” http://www.sju.edu/int/academics/cas/resources/gppc/pdf/Karen%20R.%20Zwier.pdf
2 E. Capanna. “Lazzaro Spallanzani: At the Roots of Modern Biology.” Journal of Experimental Zoology 285 no. 3 (1999):178–196.
3 R. Mancini, M. Nigro, G. Ippolito. “Lazzaro Spallanzani and His Refutation of the Theory of Spontaneous Generation.” Le Infezioni in Medicina 15 no. 3 (2007):199–206.
4 R. Vallery-Radot. The Life of Pasteur , trans. R.L. Devonshire. New York: McClure, Phillips and Co, 1902, 1:142.

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Book title: Microbiology
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2.1 Spontaneous Generation

Learning objectives.

Explain the theory of spontaneous generation and why people once accepted it as an explanation for the existence of certain types of organisms
Explain how certain individuals (van Helmont, Redi, Needham, Spallanzani, and Pasteur) tried to prove or disprove spontaneous generation

The Theory of Spontaneous Generation

The Greek philosopher Aristotle (384–322 BC) was one of the earliest recorded scholars to articulate the theory of spontaneous generation , the notion that life can arise from nonliving matter. Aristotle proposed that life arose from nonliving material if the material contained pneuma (“vital heat”). As evidence, he noted several instances of the appearance of animals from environments previously devoid of such animals, such as the seemingly sudden appearance of fish in a new puddle of water. [1]

This theory persisted into the 17th century, when scientists undertook additional experimentation to support or disprove it. By this time, the proponents of the theory cited how frogs simply seem to appear along the muddy banks of the Nile River in Egypt during the annual flooding. Others observed that mice simply appeared among grain stored in barns with thatched roofs. When the roof leaked and the grain molded, mice appeared. Jan Baptista van Helmont, a 17th century Flemish scientist, proposed that mice could arise from rags and wheat kernels left in an open container for 3 weeks. In reality, such habitats provided ideal food sources and shelter for mouse populations to flourish.

However, one of van Helmont’s contemporaries, Italian physician Francesco Redi (1626–1697), performed an experiment in 1668 that was one of the first to refute the idea that maggots (the larvae of flies) spontaneously generate on meat left out in the open air. He predicted that preventing flies from having direct contact with the meat would also prevent the appearance of maggots. Redi left meat in each of six containers ( Figure 2 .2 ). Two were open to the air, two were covered with gauze, and two were tightly sealed. His hypothesis was supported when maggots developed in the uncovered jars, but no maggots appeared in either the gauze-covered or the tightly sealed jars. He concluded that maggots could only form when flies were allowed to lay eggs in the meat, and that the maggots were the offspring of flies, not the product of spontaneous generation.

Francesco Redi’s experimental setup consisted of an open container, a container sealed with a cork top, and a container covered in mesh that let in air but not flies. Maggots only appeared on the meat in the open container. However, maggots were also found on the gauze of the gauze-covered container.

In 1745, John Needham (1713–1781) published a report of his own experiments, in which he briefly boiled broth infused with plant or animal matter, hoping to kill all preexisting microbes. [2] He then sealed the flasks. After a few days, Needham observed that the broth had become cloudy and a single drop contained numerous microscopic creatures. He argued that the new microbes must have arisen spontaneously. In reality, however, he likely did not boil the broth enough to kill all preexisting microbes.

Lazzaro Spallanzani (1729–1799) did not agree with Needham’s conclusions, however, and performed hundreds of carefully executed experiments using heated broth. [3] As in Needham’s experiment, broth in sealed jars and unsealed jars was infused with plant and animal matter. Spallanzani’s results contradicted the findings of Needham: Heated but sealed flasks remained clear, without any signs of spontaneous growth, unless the flasks were subsequently opened to the air. This suggested that microbes were introduced into these flasks from the air. In response to Spallanzani’s findings, Needham argued that life originates from a “life force” that was destroyed during Spallanzani’s extended boiling. Any subsequent sealing of the flasks then prevented new life force from entering and causing spontaneous generation ( Figure 2 .3 ).

(a) Francesco Redi, who demonstrated that maggots were the offspring of flies, not products of spontaneous generation. (b) John Needham, who argued that microbes arose spontaneously in broth from a “life force.” (c) Lazzaro Spallanzani, whose experiments with broth aimed to disprove those of Needham.

Describe the theory of spontaneous generation and some of the arguments used to support it.
Explain how the experiments of Redi and Spallanzani challenged the theory of spontaneous generation.

Disproving Spontaneous Generation

The debate over spontaneous generation continued well into the 19th century, with scientists serving as proponents of both sides. To settle the debate, the Paris Academy of Sciences offered a prize for resolution of the problem. Louis Pasteur, a prominent French chemist who had been studying microbial fermentation and the causes of wine spoilage, accepted the challenge. In 1858, Pasteur filtered air through a gun-cotton filter and, upon microscopic examination of the cotton, found it full of microorganisms, suggesting that the exposure of a broth to air was not introducing a “life force” to the broth but rather airborne microorganisms.

Later, Pasteur made a series of flasks with long, twisted necks (“swan-neck” flasks), in which he boiled broth to sterilize it ( Figure 2 .4 ). His design allowed air inside the flasks to be exchanged with air from the outside, but prevented the introduction of any airborne microorganisms, which would get caught in the twists and bends of the flasks’ necks. If a life force besides the airborne microorganisms were responsible for microbial growth within the sterilized flasks, it would have access to the broth, whereas the microorganisms would not. He correctly predicted that sterilized broth in his swan-neck flasks would remain sterile as long as the swan necks remained intact. However, should the necks be broken, microorganisms would be introduced, contaminating the flasks and allowing microbial growth within the broth.

Pasteur’s set of experiments irrefutably disproved the theory of spontaneous generation and earned him the prestigious Alhumbert Prize from the Paris Academy of Sciences in 1862. In a subsequent lecture in 1864, Pasteur articulated “ Omne vivum ex vivo ” (“Life only comes from life”). In this lecture, Pasteur recounted his famous swan- neck flask experiment, stating that “…life is a germ and a germ is life. Never will the doctrine of spontaneous generation recover from the mortal blow of this simple experiment.” [4] To Pasteur’s credit, it never has.

(a) French scientist Louis Pasteur, who definitively refuted the long-disputed theory of spontaneous generation. (b) The unique swan-neck feature of the flasks used in Pasteur ’s experiment allowed air to enter the flask but prevented the entry of bacterial and fungal spores. (c) Pasteur’s experiment consisted of two parts. In the first part, the broth in the flask was boiled to sterilize it. When this broth was cooled, it remained free of contamination. In the second part of the experiment, the flask was boiled and then the neck was broken off. The broth in this flask became contaminated.

How did Pasteur’s experimental design allow air, but not microbes, to enter, and why was this important?
What was the control group in Pasteur’s experiment and what did it show?
K. Zwier. “Aristotle on Spontaneous Generation.” http://www.sju.edu/int/academics/cas/resources/gppc/pdf/Karen%20R.%20Zwier.pdf ↵
E. Capanna. “Lazzaro Spallanzani: At the Roots of Modern Biology.” Journal of Experimental Zoology 285 no. 3 (1999):178–196. ↵
R. Mancini, M. Nigro, G. Ippolito. “Lazzaro Spallanzani and His Refutation of the Theory of Spontaneous Generation.” Le Infezioni in Medicina 15 no. 3 (2007):199–206. ↵
R. Vallery-Radot. The Life of Pasteur, trans. R.L. Devonshire. New York: McClure, Phillips and Co, 1902, 1:142. ↵

Allied Health Microbiology Copyright © 2019 by Open Stax and Linda Bruslind is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License , except where otherwise noted.

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3 1.2 Spontaneous Generation

Learning objectives.

Explain the theory of spontaneous generation and why people once accepted it as an explanation for the existence of certain types of organisms
Explain how certain individuals (van Helmont, Redi, Needham, Spallanzani, and Pasteur) tried to prove or disprove spontaneous generation

CLINICAL FOCUS: Part 1

What types of respiratory disease may be responsible?

Jump to the next Clinical Focus box

The Theory of Spontaneous Generation

The Greek philosopher Aristotle (384–322 BC) was one of the earliest recorded scholars to articulate the theory of spontaneous generation, the notion that life can arise from nonliving matter. Aristotle proposed that life arose from nonliving material if the material contained pneuma (“vital heat”). As evidence, he noted several instances of the appearance of animals from environments previously devoid of such animals, such as the seemingly sudden appearance of fish in a new puddle of water. [1]

This theory persisted into the 17th century, when scientists undertook additional experimentation to support or disprove it. By this time, the proponents of the theory cited how frogs simply seem to appear along the muddy banks of the Nile River in Egypt during the annual flooding. Others observed that mice simply appeared among grain stored in barns with thatched roofs. When the roof leaked and the grain moulded, mice appeared. Jan Baptista van Helmont , a 17th century Flemish scientist, proposed that mice could arise from rags and wheat kernels left in an open container for 3 weeks. In reality, such habitats provided ideal food sources and shelter for mouse populations to flourish.

However, one of van Helmont’s contemporaries, Italian physician Francesco Redi (1626–1697), performed an experiment in 1668 that was one of the first to refute the idea that maggots (the larvae of flies) spontaneously generate on meat left out in the open air. He predicted that preventing flies from having direct contact with the meat would also prevent the appearance of maggots. Redi left meat in each of six containers ( Figure 1.10 ). Two were open to the air, two were covered with gauze, and two were tightly sealed. His hypothesis was supported when maggots developed in the uncovered jars, but no maggots appeared in either the gauze-covered or the tightly sealed jars. He concluded that maggots could only form when flies were allowed to lay eggs in the meat, and that the maggots were the offspring of flies, not the product of spontaneous generation.

An open container with meat has flies and the formation of maggots in meat. A cork-sealed container of meat has no flies and no formation of maggots in meat. A gauze covered container of meat has flies and maggots on the surface of the gauze but no maggots in the meat.

In 1745, John Needham (1713–1781) published a report of his own experiments, in which he briefly boiled broth infused with plant or animal matter, hoping to kill all preexisting microbes. [2] He then sealed the flasks. After a few days, Needham observed that the broth had become cloudy and a single drop contained numerous microscopic creatures. He argued that the new microbes must have arisen spontaneously. In reality, however, he likely did not boil the broth enough to kill all preexisting microbes.

a) drawing of Francesco Redi. B) drawing of John Needham c) drawing of Lazzaro Spallanzani.

Describe the theory of spontaneous generation and some of the arguments used to support it.
Explain how the experiments of Redi and Spallanzani challenged the theory of spontaneous generation.

Disproving Spontaneous Generation

Later, Pasteur made a series of flasks with long, twisted necks (“swan-neck” flasks), in which he boiled broth to sterilize it ( Figure 1.12 ). His design allowed air inside the flasks to be exchanged with air from the outside, but prevented the introduction of any airborne microorganisms, which would get caught in the twists and bends of the flasks’ necks. If a life force besides the airborne microorganisms were responsible for microbial growth within the sterilized flasks, it would have access to the broth, whereas the microorganisms would not. He correctly predicted that sterilized broth in his swan-neck flasks would remain sterile as long as the swan necks remained intact. However, should the necks be broken, microorganisms would be introduced, contaminating the flasks and allowing microbial growth within the broth.

a) Photo of Louis Pasteur b) Photo of Pasteur’s swan-necked flask, c) A drawing of Pasteur’s experiment that disproved the theory of spontaneous generation.

How did Pasteur’s experimental design allow air, but not microbes, to enter, and why was this important?
What was the control group in Pasteur’s experiment and what did it show?

Key Takeaways

The theory of spontaneous generation states that life arose from nonliving matter. It was a long-held belief dating back to Aristotle and the ancient Greeks.
Experimentation by Francesco Redi in the 17th century presented the first significant evidence refuting spontaneous generation by showing that flies must have access to meat for maggots to develop on the meat. Prominent scientists designed experiments and argued both in support of (John Needham) and against (Lazzaro Spallanzani) spontaneous generation.
Louis Pasteur is credited with conclusively disproving the theory of spontaneous generation with his famous swan-neck flask experiment. He subsequently proposed that “life only comes from life.”

Multiple Choice

Fill in the blank, short answer.

Explain in your own words Pasteur’s swan-neck flask experiment.
Explain why the experiments of Needham and Spallanzani yielded in different results even though they used similar methodologies.

Critical Thinking

What would the results of Pasteur’s swan-neck flask experiment have looked like if they supported the theory of spontaneous generation?
https://link.springer.com/content/pdf/10.1007%2Fs10739-017-9494-7.pdf ↵
E. Capanna. “Lazzaro Spallanzani: At the Roots of Modern Biology.” Journal of Experimental Zoology 285 no. 3 (1999):178–196. ↵
R. Mancini, M. Nigro, G. Ippolito. “Lazzaro Spallanzani and His Refutation of the Theory of Spontaneous Generation.” Le Infezioni in Medicina 15 no. 3 (2007):199–206. ↵
R. Vallery-Radot. The Life of Pasteur , trans. R.L. Devonshire. New York: McClure, Phillips and Co, 1902, 1:142. ↵

DeSales Microbiology Copyright © 2022 by DeSales University & Dr. Dia Beachboard is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License , except where otherwise noted.

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3. The Cell

3.1 Spontaneous Generation

Learning objectives.

Explain the theory of spontaneous generation and why people once accepted it as an explanation for the existence of certain types of organisms
Explain how certain individuals (van Helmont, Redi, Needham, Spallanzani, and Pasteur) tried to prove or disprove spontaneous generation

CLINICAL FOCUS: Part 1

What types of respiratory disease may be responsible?

Jump to the next Clinical Focus box

The Theory of Spontaneous Generation

The Greek philosopher Aristotle (384–322 BC) was one of the earliest recorded scholars to articulate the theory of spontaneous generation, the notion that life can arise from nonliving matter. Aristotle proposed that life arose from nonliving material if the material contained pneuma (“vital heat”). As evidence, he noted several instances of the appearance of animals from environments previously devoid of such animals, such as the seemingly sudden appearance of fish in a new puddle of water. [1]

This theory persisted into the 17th century, when scientists undertook additional experimentation to support or disprove it. By this time, the proponents of the theory cited how frogs simply seem to appear along the muddy banks of the Nile River in Egypt during the annual flooding. Others observed that mice simply appeared among grain stored in barns with thatched roofs. When the roof leaked and the grain moulded, mice appeared. Jan Baptista van Helmont , a 17th century Flemish scientist, proposed that mice could arise from rags and wheat kernels left in an open container for 3 weeks. In reality, such habitats provided ideal food sources and shelter for mouse populations to flourish.

In 1745, John Needham (1713–1781) published a report of his own experiments, in which he briefly boiled broth infused with plant or animal matter, hoping to kill all preexisting microbes. [2] He then sealed the flasks. After a few days, Needham observed that the broth had become cloudy and a single drop contained numerous microscopic creatures. He argued that the new microbes must have arisen spontaneously. In reality, however, he likely did not boil the broth enough to kill all preexisting microbes.

Describe the theory of spontaneous generation and some of the arguments used to support it.
Explain how the experiments of Redi and Spallanzani challenged the theory of spontaneous generation.

Disproving Spontaneous Generation

How did Pasteur’s experimental design allow air, but not microbes, to enter, and why was this important?
What was the control group in Pasteur’s experiment and what did it show?

Key Takeaways

The theory of spontaneous generation states that life arose from nonliving matter. It was a long-held belief dating back to Aristotle and the ancient Greeks.
Experimentation by Francesco Redi in the 17th century presented the first significant evidence refuting spontaneous generation by showing that flies must have access to meat for maggots to develop on the meat. Prominent scientists designed experiments and argued both in support of (John Needham) and against (Lazzaro Spallanzani) spontaneous generation.
Louis Pasteur is credited with conclusively disproving the theory of spontaneous generation with his famous swan-neck flask experiment. He subsequently proposed that “life only comes from life.”

Multiple Choice

Fill in the blank, short answer.

Explain in your own words Pasteur’s swan-neck flask experiment.
Explain why the experiments of Needham and Spallanzani yielded in different results even though they used similar methodologies.

Critical Thinking

What would the results of Pasteur’s swan-neck flask experiment have looked like if they supported the theory of spontaneous generation?

Media Attributions

OSC_Microbio_03_01_Rediexpt
https://link.springer.com/content/pdf/10.1007%2Fs10739-017-9494-7.pdf ↵
E. Capanna. “Lazzaro Spallanzani: At the Roots of Modern Biology.” Journal of Experimental Zoology 285 no. 3 (1999):178–196. ↵
R. Mancini, M. Nigro, G. Ippolito. “Lazzaro Spallanzani and His Refutation of the Theory of Spontaneous Generation.” Le Infezioni in Medicina 15 no. 3 (2007):199–206. ↵
R. Vallery-Radot. The Life of Pasteur , trans. R.L. Devonshire. New York: McClure, Phillips and Co, 1902, 1:142. ↵

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Home → Features → History and Humanities → People

Louis Pasteur, Spontaneous Generation, and Germ Theory

“For I have kept from them, and am still keeping from them, that one thing which is above the power of man to make; I have kept from them the germs that float in the air, I have kept them from life.” - Louis Pasteur

“For I have kept from them, and am still keeping from them, that one thing which is above the power of man to make; I have kept from them the germs that float in the air, I have kept them from life.” – Louis Pasteur (1)

May 19, 1861 is a date that probably doesn’t ring a bell or cause any light bulbs to go off in terms of huge scientific events. In the United States, people weren’t thinking too much about science. The Civil War was only five weeks old, and Union and Confederate gunships were trying, to no avail, to capture the Chesapeake Bay (2) .

In England, Charles Darwin’s On the Origin of Species had already been in circulation for a year and a half, leaving scientific revolution and controversy in its wake. (3) Elsewhere in Europe, Gregor Mendel still tended the pea plants that became the basis of what we now know as “classical” genetics after he presented his work to the scientific world in 1865 (4) . And in Paris, a chemist named Louis Pasteur presented an experiment in front of his colleagues at the Paris Society for Chemistry that would turn the scientific world and much of what we believed on its head (5) .

Prior to Pasteur’s experiment, a belief called “spontaneous generation” was a prevalent scientific method to explain how life came to be. This belief outlined that life can essentially arise from anything, even out of thin air. So if a piece of meat spoiled, the cause of the spoilage simply materialized from the air!

What Pasteur did was put the belief of spontaneous generation to rest with a simple, yet brilliant experiment. Pasteur boiled some nutrient broth inside a flask with a long, twisted neck. The flask, while still open to the air, did not allow any microbes to enter the main area of the flask where the sterile broth was. Any bacteria in the air couldn’t pass through the long neck of the flask to get to the broth inside. No bacteria meant no contamination, and the broth stayed sterile for one whole year! Pasteur then broke the neck of the flask and exposed the broth to the microbe-filled air, which contaminated the broth in short order.

Life Comes From Life

What is the ultimate impact of Pasteur’s experiment? He didn’t win the Nobel Prize for it (the first Nobel Prizes were awarded in 1901, and Pasteur died in 1895) (1, 6) .

But there came a shift in attitude regarding how life came to be. The idea that “life comes from life” is now one of the major tenets of biology. Its significance is right up there with evolution and the cell theory (7) .

Even more significantly, Pasteur’s experiment had an even greater impact on medicine. In the years following Pasteur’s experiment, Pasteur and one of his contemporaries (and eventually, his bitter rival) Robert Koch began studying various diseases closely and concluded that specific microbes have the ability to cause specific diseases (1, 8, 9) .

This is the germ theory of disease. This theory led to the successful identification and treatment of many microbial diseases (1) , saving millions of lives and contributing to the development of what we know today as modern medicine.

All because of a chemist and his funny-looking flask.

References:

Talaro, Kathleen Park, and Barry Chess. Foundations in Microbiology , ninth edition. New York: McGraw-Hill (2015).
Battle Summary: Sewell’s Point, VA . CWSCA Battle Summaries: The American Battlefield Preservation Program (ABPP) . Retrieved from https://www.nps.gov/abpp/Battles/va001.htm
Darwin, Charles. On the Origin of Species by Means of Natural Selection . London: John Murray (1859). Retrieved from https://www.gutenberg.org/files/1228/1228-h/1228-h.htm
Mendel, Gregor.Versuche über Pflanzen-Hybriden. Verh. Naturforsch. Ver. Brünn 4: 3–47 (1866) (Article in German). Retrieved from http://www.biodiversitylibrary.org/item/124139#page/133/mode/1up
Pasteur, Louis. Sur les corpuscles organisés qui existent dans l’atmosphère: Examen de la doctrine des générations spontanées. Leçon Professée a la Société Chimique de Paris, le 19 Mai 1861 (Article in French).
Nobel Prize Facts. Retrieved from http://www.nobelprize.org/nobel_prizes/facts/
Simon, Eric J., Dickey, Jean L., Hogan, Kelly A, and Jane B. Reece. Campbell Essential Biology, sixth edition. New York: Pearson Higher Education (2016).
Smith, Kendall. Louis Pasteur, the father of immunology? Frontiers in Immunology 3(68), 1-10 (April 2012).
Blevins, Steve M., and Bronze, Michael S. Robert Koch and the ‘golden age’ of bacteriology. International Journal of Infectious Diseases 14: e744–e751 (2010).

About the Author

Craig Fenn is in his fourth year of teaching for the American Public University in the School of Science, Technology, Engineering and Math, with a primary teaching assignment of SCIN 130 (Introduction to Biology with Lab). His primary employer is at Reading Area Community College, where he serves as the course lead for Principles of Biology and Microbiology as well as the chair of the Campus Life Committee. He is a native of Connecticut currently living outside of Lancaster, PA.

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Louis pasteur’s devotion to truth transformed what we know about health and disease.

A photo of Louis Pasteur's head surrounded by illustrations of scientific equipment, leaves, and swirls

Louis Pasteur demonstrated, more dramatically than any other scientist, the benefit of science for humankind.

Sam Falconer

How Pasteur developed pasteurization

In his youth, Pasteur did not especially excel as a student. His interests inclined toward art rather than science, and he did display exceptional skill at drawing and painting. But in light of career considerations (his father wanted him to be a scholar), Pasteur abandoned art for science and so applied to the prestigious École Normale Supérieure in Paris for advanced education. He finished 15th in the competitive entrance examination, good enough to secure admission. But not good enough for Pasteur. He spent another year on further studies emphasizing physical sciences and then took the École Normale exam again, finishing fourth. That was good enough, and he entered the school in 1843. There he earned his doctoral degree, in physics and chemistry, in 1847.

Among his special interests at the École Normale was crystallography. In particular he was drawn to investigate tartaric acid. It’s a chemical found in grapes responsible for tartar, a potassium compound that collects on the surfaces of wine vats. Scientists had recently discovered that tartaric acid possesses the intriguing power of twisting light — that is, rotating the orientation of light waves’ vibrations. In light that has been polarized (by passing it through certain crystals, filters or some sunglasses), the waves are all aligned in a single plane. Light passing through a tartaric acid solution along one plane emerges in a different plane.

Even more mysteriously, another acid (paratartaric acid, or racemic acid), with the exact same chemical composition as tartaric acid, did not twist light at all. Pasteur found that suspicious. He began a laborious study of the crystals of salts derived from the two acids. He discovered that racemic acid crystals could be sorted into two asymmetric mirror-image shapes, like pairs of right-handed and left-handed gloves. All the tartaric acid crystals, on the other hand, had shapes with identical asymmetry, analogous to gloves that were all right-handed.

An illustration of two crystal forms of racemic acid

Pasteur deduced that the asymmetry in the crystals reflected the asymmetric arrangement of atoms in their constituent molecules. Tartaric acid twisted light because of the asymmetry of its molecules, while in racemic acid, the two opposite shapes canceled out each other’s twisting effects.

Pasteur built the rest of his career on this discovery. His research on tartaric acid and wine led eventually to profound realizations about the relationship between microbes and human disease. Before Pasteur, most experts asserted that fermentation was a natural nonbiological chemical process. Yeast, a necessary ingredient in the fermenting fluid, was supposedly a lifeless chemical acting as a catalyst. Pasteur’s experiments showed yeast to be alive, a peculiar kind of “small plant” (now known to be a fungus) that caused fermentation by biological activity.

Pasteur demonstrated that, in the absence of air, yeast acquired oxygen from sugar, converting the sugar to alcohol in the process. “Fermentation by yeast,” he wrote, is “the direct consequence of the processes of nutrition,” a property of a “minute cellular plant … performing its respiratory functions.” Or more succinctly, he proclaimed that “fermentation … is life without air.” (Later scientists found that yeast accomplished fermentation by emitting enzymes that catalyzed the reaction.)

Pasteur also noticed that additional microorganisms present during fermentation could be responsible for the process going awry, a problem threatening the viability of French winemaking and beer brewing. He solved that problem by developing a method of heating that eliminated the bad microorganisms while preserving the quality of the beverages. This method, called “pasteurization,” was later applied to milk, eliminating the threat of illness from drinking milk contaminated by virulent microorganisms. Pasteurization became standard public health practice in the 20th century.

Incorporating additional insights from studies of other forms of fermentation, Pasteur summarized his work on microbial life in a famous paper published in 1857. “This paper can truly be regarded as the beginning of scientific microbiology,” wrote the distinguished microbiologist René Dubos, who called it “one of the most important landmarks of biochemical and biological sciences.”

The germ theory of disease is born

Pasteur’s investigations of the growth of microorganisms in fermentation collided with another prominent scientific issue: the possibility of spontaneous generation of life. Popular opinion even among many scientists held that microbial life self-generated under the proper conditions (spoiled meat, for example). Demonstrations by the 17th century Italian scientist Francesco Redi challenged that belief , but the case against spontaneous generation was not airtight.

A photo of a double flask in the foreground and another flask in the background, both used by Louis Pasteur

In the early 1860s Pasteur undertook a series of experiments that should have left no doubt that spontaneous generation, under conditions encountered on Earth today, was an illusion. Yet he was nevertheless accosted by critics, such as the French biologist Charles-Philippe Robin, to whom he returned verbal fire. “We trust that the day will come when M. Robin will … acknowledge that he has been in error on the subject of the doctrine of spontaneous generation, which he continues to affirm, without adducing any direct proofs in support of it,” Pasteur remarked.

It was his work on spontaneous generation that led Pasteur directly to the development of the germ theory of disease.

For centuries people had suspected that some diseases must be transmitted from person to person by close contact. But determining exactly how that happened seemed beyond the scope of scientific capabilities. Pasteur, having discerned the role of germs in fermentation, saw instantly that something similar to what made wine go bad might also harm human health.

After disproving spontaneous generation, he realized that there must exist “transmissible, contagious, infectious diseases of which the cause lies essentially and solely in the presence of microscopic organisms.” For some diseases, at least, it was necessary to abandon “the idea of … an infectious element suddenly originating in the bodies of men or animals.” Opinions to the contrary, he wrote, gave rise “to the gratuitous hypothesis of spontaneous generation” and were “fatal to medical progress.”

His first foray into applying the germ theory of disease came during the late 1860s in response to a decline in French silk production because of diseases afflicting silkworms. After success in tackling the silkworms’ maladies, he turned to anthrax, a terrible illness for cattle and humans alike. Many medical experts had long suspected that some form of bacteria caused anthrax, but it was Pasteur’s series of experiments that isolated the responsible microorganism, verifying the germ theory beyond doubt. (Similar work by Robert Koch in Germany around the same time provided further confirmation.)

Understanding anthrax’s cause led to the search for a way to prevent it. In this case, a fortuitous delay in Pasteur’s experiments with cholera in chickens produced a fortunate surprise. In the spring of 1879 he had planned to inject chickens with cholera bacteria he had cultured, but he didn’t get around to it until after his summer vacation. When he injected his chickens in the fall, they unexpectedly failed to get sick. So Pasteur prepared a fresh bacterial culture and brought in a new batch of chickens.

When both the new chickens and the previous batch were given the fresh bacteria, the new ones all died, while nearly all of the original chickens still remained healthy. And so, Pasteur realized, the original culture had weakened in potency over the summer and was unable to cause disease, while the new, obviously potent culture did not harm the chickens previously exposed to the weaker culture. “These animals have been vaccinated,” he declared.

Vaccination, of course, had been invented eight decades earlier, when British physician Edward Jenner protected people from smallpox by first exposing them to cowpox, a similar disease acquired from cows. (Vaccination comes from cowpox’s medical name, vaccinia, from vacca , Latin for cow.) Pasteur realized that the chickens surprisingly displayed a similar instance of vaccination because he was aware of Jenner’s discovery. “Chance favors the prepared mind,” Pasteur was famous for saying.

Because of his work on the germ theory of disease, Pasteur’s mind was prepared to grasp the key role of microbes in the prevention of smallpox, something Jenner could not have known. And Pasteur instantly saw that the specific idea of vaccination for smallpox could be generalized to other diseases. “Instead of depending on the chance finding of naturally occurring immunizing agents, as cowpox was for smallpox,” Dubos observed, “it should be possible to produce vaccines at will in the laboratory.”

Pasteur cultured the anthrax microbe and weakened it for tests in farm animals. Success in such tests not only affirmed the correctness of the germ theory of disease, but also allowed it to gain a foothold in devising new medical practices.

Later Pasteur confronted an even more difficult microscopic foe, the virus that causes rabies. He had begun intense experiments on rabies, a horrifying disease that’s almost always fatal, caused usually by the bites of rabid dogs or other animals. His experiments failed to find any bacterial cause for rabies, leading him to realize that it must be the result of some agent too small to see with his microscope. He could not grow cultures in lab dishes of what he could not see. So instead he decided to grow the disease-causing agent in living tissue — the spinal cords of rabbits. He used dried-out strips of spinal cord from infected rabbits to vaccinate other animals that then survived rabies injections.

Pasteur hesitated to test his rabies treatment on humans. Still, in 1885 when a mother brought to his lab a 9-year-old boy who had been badly bitten by a rabid dog, Pasteur agreed to administer the new vaccine. After a series of injections, the boy recovered fully. Soon more requests came for the rabies vaccine, and by early the next year over 300 rabies patients had received the vaccine and survived, with only one death among them.

Popularly hailed as a hero, Pasteur was also vilified by some hostile doctors, who considered him an uneducated interloper in medicine. Vaccine opponents complained that his vaccine was an untested method that might itself cause death. But of course, critics had also rejected Pasteur’s view of fermentation, the germ theory of disease and his disproof of spontaneous generation.

A cartoon from the magazine Puck in 1885 showing people in a line for Louis Pasteur's rabies vaccine

Pasteur stood his ground and eventually prevailed (although he did not turn out to be right about everything). His attitude and legacy of accomplishments inspired 20th century scientists to develop vaccines for more than a dozen deadly diseases. Still more diseases succumbed to antibiotics, following the discovery of penicillin by Alexander Fleming — who declared, “Without Pasteur I would have been nothing.”

Even in Pasteur’s own lifetime, thanks to his defeat of rabies, his public reputation was that of a genius.

Pasteur’s scientific legacy

As geniuses go, Pasteur was the opposite of Einstein. To get inspiration for his theories, Einstein imagined riding aside a light beam or daydreamed about falling off a ladder. Pasteur stuck to experiments. He typically initiated his experiments with a suspected result in mind, but he was scrupulous in verifying the conclusions he drew from them. Preconceived ideas, he said, can guide the experimenter’s interrogation of nature but must be abandoned in light of contrary evidence. “The greatest derangement of the mind,” he declared, “is to believe in something because one wishes it to be so.”

So even when Pasteur was sure his view was correct, he insisted on absolute proof, conducting many experiments over and over with variations designed to rule out all but the true interpretation.

“If Pasteur was a genius, it was not through ethereal subtlety of mind,” wrote Pasteur scholar Gerald Geison. Rather, he exhibited “clear-headedness, extraordinary experimental skill and tenacity — almost obstinacy — of purpose.”

This painting depicts French President Sadi Carnot helping Louis Pasteur walk across the stage during a ceremony held at the Sorbonne in Paris in honor of Pasteur’s 70th birthday

His tenacity, or obstinacy, helped him persevere through several personal tragedies, such as the deaths of three of his daughters, in 1859, 1865 and 1866. And then in 1868 he suffered a cerebral hemorrhage that left him paralyzed on his left side. But that did not slow his pace or impair continuing his investigations.

“Whatever the circumstances in which he had to work, he never submitted to them, but instead molded them to the demands of his imagination and his will,” Dubos wrote. “He was probably the most dedicated servant that science ever had.”

To the end of his life, Pasteur remained dedicated to science and the scientific method, stressing the importance of experimental science for the benefit of society. Laboratories are “sacred institutions,” he asserted. “Demand that they be multiplied and adorned; they are the temples of wealth and of the future.”

Three years before his death in 1895, Pasteur further extolled the value of science and asserted his optimism that the scientific spirit would prevail. In an address, delivered for him by his son, at a ceremony at the Sorbonne in Paris, he expressed his “invincible belief … that science and peace will triumph over ignorance and war, that nations will unite, not to destroy, but to build, and that the future will belong to those who will have done most for suffering humanity.”

A painted portrait of Louis Pasteur on the cover of a french newspaper from 1895

Two hundred years after his birth , ignorance and war remain perniciously prominent, as ineradicable as the microbes that continue to threaten public health, with the virus causing COVID-19 the latest conspicuous example. Vaccines, though, have substantially reduced the risks from COVID-19, extending the record of successful vaccines that have already tamed not only smallpox and rabies, but also polio, measles and a host of other once deadly maladies .

Yet even though vaccines have saved countless millions of lives, some politicians and so-called scientists who deny or ignore overwhelming evidence continue to condemn vaccines as more dangerous than the diseases they prevent. True, some vaccines can induce bad reactions, even fatal in a few cases out of millions of vaccinations. But shunning vaccines today, as advocated in artificially amplified social media outrage, is like refusing to eat because some people choke to death on sandwiches.

Today, Pasteur would be vilified just as he was in his own time, probably by some people who don’t even realize that they can safely drink milk because of him. Nobody knows exactly what Pasteur would say to these people now. But it’s certain that he would stand up for truth and science, and would be damn sure to tell everybody to get vaccinated.

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Spontaneous Generation

Learning objectives.

Explain the theory of spontaneous generation and why people once accepted it as an explanation for the existence of certain types of organisms
Explain how certain individuals (van Helmont, Redi, Needham, Spallanzani, and Pasteur) tried to prove or disprove spontaneous generation

Clinical Focus: Anika, Part 1

Anika is a 19-year-old college student living in the dormitory. In January, she came down with a sore throat, headache, mild fever, chills, and a violent but unproductive (i.e., no mucus) cough. To treat these symptoms, Anika began taking an over-the-counter cold medication, which did not seem to work. In fact, over the next few days, while some of Anika’s symptoms began to resolve, her cough and fever persisted, and she felt very tired and weak.

What types of respiratory disease may be responsible?

We’ll return to Anika’s example in later pages.

The Theory of Spontaneous Generation

The Greek philosopher Aristotle (384–322 BC) was one of the earliest recorded scholars to articulate the theory of spontaneous generation , the notion that life can arise from nonliving matter. Aristotle proposed that life arose from nonliving material if the material contained pneuma (“vital heat”). As evidence, he noted several instances of the appearance of animals from environments previously devoid of such animals, such as the seemingly sudden appearance of fish in a new puddle of water. [1]

This theory persisted into the seventeenth century, when scientists undertook additional experimentation to support or disprove it. By this time, the proponents of the theory cited how frogs simply seem to appear along the muddy banks of the Nile River in Egypt during the annual flooding. Others observed that mice simply appeared among grain stored in barns with thatched roofs. When the roof leaked and the grain molded, mice appeared. Jan Baptista van Helmont , a seventeenth century Flemish scientist, proposed that mice could arise from rags and wheat kernels left in an open container for 3 weeks. In reality, such habitats provided ideal food sources and shelter for mouse populations to flourish.

However, one of van Helmont’s contemporaries, Italian physician Francesco Redi (1626–1697), performed an experiment in 1668 that was one of the first to refute the idea that maggots (the larvae of flies) spontaneously generate on meat left out in the open air. He predicted that preventing flies from having direct contact with the meat would also prevent the appearance of maggots. Redi left meat in each of six containers (Figure 1). Two were open to the air, two were covered with gauze, and two were tightly sealed. His hypothesis was supported when maggots developed in the uncovered jars, but no maggots appeared in either the gauze-covered or the tightly sealed jars. He concluded that maggots could only form when flies were allowed to lay eggs in the meat, and that the maggots were the offspring of flies, not the product of spontaneous generation.

Figure 1. Francesco Redi’s experimental setup consisted of an open container, a container sealed with a cork top, and a container covered in mesh that let in air but not flies. Maggots only appeared on the meat in the open container. However, maggots were also found on the gauze of the gauze-covered container.

In 1745, John Needham (1713–1781) published a report of his own experiments, in which he briefly boiled broth infused with plant or animal matter, hoping to kill all preexisting microbes. [2] He then sealed the flasks. After a few days, Needham observed that the broth had become cloudy and a single drop contained numerous microscopic creatures. He argued that the new microbes must have arisen spontaneously. In reality, however, he likely did not boil the broth enough to kill all preexisting microbes.

Figure 2. (a) Francesco Redi, who demonstrated that maggots were the offspring of flies, not products of spontaneous generation. (b) John Needham, who argued that microbes arose spontaneously in broth from a “life force.” (c) Lazzaro Spallanzani, whose experiments with broth aimed to disprove those of Needham.

Think about It

Describe the theory of spontaneous generation and some of the arguments used to support it.
Explain how the experiments of Redi and Spallanzani challenged the theory of spontaneous generation.

Disproving Spontaneous Generation

The debate over spontaneous generation continued well into the nineteenth century, with scientists serving as proponents of both sides. To settle the debate, the Paris Academy of Sciences offered a prize for resolution of the problem. Louis Pasteur, a prominent French chemist who had been studying microbial fermentation and the causes of wine spoilage, accepted the challenge. In 1858, Pasteur filtered air through a gun-cotton filter and, upon microscopic examination of the cotton, found it full of microorganisms, suggesting that the exposure of a broth to air was not introducing a “life force” to the broth but rather airborne microorganisms.

Later, Pasteur made a series of flasks with long, twisted necks (“swan-neck” flasks), in which he boiled broth to sterilize it (Figure 3). His design allowed air inside the flasks to be exchanged with air from the outside, but prevented the introduction of any airborne microorganisms, which would get caught in the twists and bends of the flasks’ necks. If a life force besides the airborne microorganisms were responsible for microbial growth within the sterilized flasks, it would have access to the broth, whereas the microorganisms would not. He correctly predicted that sterilized broth in his swan-neck flasks would remain sterile as long as the swan necks remained intact. However, should the necks be broken, microorganisms would be introduced, contaminating the flasks and allowing microbial growth within the broth.

Pasteur’s set of experiments irrefutably disproved the theory of spontaneous generation and earned him the prestigious Alhumbert Prize from the Paris Academy of Sciences in 1862. In a subsequent lecture in 1864, Pasteur articulated “ Omne vivum ex vivo ” (“Life only comes from life”). In this lecture, Pasteur recounted his famous swan-neck flask experiment, stating that “life is a germ and a germ is life. Never will the doctrine of spontaneous generation recover from the mortal blow of this simple experiment.” [4] To Pasteur’s credit, it never has.

a) Photo of Louis Pasteur b) Photo of Pasteur’s flask – a round flask that is only opened to the outside through a long S-shaped tube. c) A drawing of Pasteur’s experiment. The top diagram shows the swan-neck flask from (b) containing broth that is being boiled to kill microorganisms in the broth. After the boiling process the cooled flask remains sterile because the curve of the flask prevents outside air from entering the flask. So, no contamination occurs. The bottom diagram shows the same flask being boiled. Next, the swan-neck is removed and the flask is opened to the environment. When the neck of the flask is broken off, bacteria reach the sterile broth and organism growth occurs. This is seen as cloudiness in the broth.

Figure 3. (a) French scientist Louis Pasteur, who definitively refuted the long-disputed theory of spontaneous generation. (b) The unique swan-neck feature of the flasks used in Pasteur’s experiment allowed air to enter the flask but prevented the entry of bacterial and fungal spores. (c) Pasteur’s experiment consisted of two parts. In the first part, the broth in the flask was boiled to sterilize it. When this broth was cooled, it remained free of contamination. In the second part of the experiment, the flask was boiled and then the neck was broken off. The broth in this flask became contaminated. (credit b: modification of work by “Wellcome Images”/Wikimedia Commons)

How did Pasteur’s experimental design allow air, but not microbes, to enter, and why was this important?
What was the control group in Pasteur’s experiment and what did it show?

Key Concepts and Summary

The theory of spontaneous generation states that life arose from nonliving matter. It was a long-held belief dating back to Aristotle and the ancient Greeks.
Experimentation by Francesco Redi in the seventeenth century presented the first significant evidence refuting spontaneous generation by showing that flies must have access to meat for maggots to develop on the meat. Prominent scientists designed experiments and argued both in support of (John Needham) and against (Lazzaro Spallanzani) spontaneous generation.
Louis Pasteur is credited with conclusively disproving the theory of spontaneous generation with his famous swan-neck flask experiment. He subsequently proposed that “life only comes from life.”

Multiple Choice

Which of the following individuals argued in favor of the theory of spontaneous generation?

Francesco Redi
Louis Pasteur
John Needham
Lazzaro Spallanzani

Which of the following individuals is credited for definitively refuting the theory of spontaneous generation using broth in swan-neck flask?

Jan Baptista van Helmont

Which of the following experimented with raw meat, maggots, and flies in an attempt to disprove the theory of spontaneous generation.

Antonie van Leeuwenhoek

Fill in the Blank

The assertion that “life only comes from life” was stated by Louis Pasteur in regard to his experiments that definitively refuted the theory of ___________.

Exposure to air is necessary for microbial growth.

Explain in your own words Pasteur’s swan-neck flask experiment.
Explain why the experiments of Needham and Spallanzani yielded in different results even though they used similar methodologies.
What would the results of Pasteur’s swan-neck flask experiment have looked like if they supported the theory of spontaneous generation?
K. Zwier. "Aristotle on Spontaneous Generation." http://www.sju.edu/int/academics/cas/resources/gppc/pdf/Karen%20R.%20Zwier.pdf ↵
E. Capanna. "Lazzaro Spallanzani: At the Roots of Modern Biology." Journal of Experimental Zoology 285 no. 3 (1999):178–196. ↵
R. Mancini, M. Nigro, G. Ippolito. "Lazzaro Spallanzani and His Refutation of the Theory of Spontaneous Generation." Le Infezioni in Medicina 15 no. 3 (2007):199–206. ↵
R. Vallery-Radot. The Life of Pasteur , trans. R.L. Devonshire. New York: McClure, Phillips and Co, 1902, 1:142. ↵
OpenStax Microbiology. Provided by : OpenStax CNX. Located at : http://cnx.org/contents/[email protected] . License : CC BY: Attribution . License Terms : Download for free at http://cnx.org/contents/[email protected]

Origin of Life: Spontaneous Generation

Spontaneous Generation

Origin of Life

Introduction
Early Earth Environment

It was once believed that life could come from nonliving things, such as mice from corn, flies from bovine manure, maggots from rotting meat, and fish from the mud of previously dry lakes. Spontaneous generation is the incorrect hypothesis that nonliving things are capable of producing life. Several experiments have been conducted to disprove spontaneous generation; a few of them are covered in the sections that follow.

Redi's Experiment and Needham's Rebuttal

In 1668, Francesco Redi, an Italian scientist, designed a scientific experiment to test the spontaneous creation of maggots by placing fresh meat in each of two different jars. One jar was left open; the other was covered with a cloth. Days later, the open jar contained maggots, whereas the covered jar contained no maggots. He did note that maggots were found on the exterior surface of the cloth that covered the jar. Redi successfully demonstrated that the maggots came from fly eggs and thereby helped to disprove spontaneous generation. Or so he thought.

In England, John Needham challenged Redi's findings by conducting an experiment in which he placed a broth, or gravy, into a bottle, heated the bottle to kill anything inside, then sealed it. Days later, he reported the presence of life in the broth and announced that life had been created from nonlife. In actuality, he did not heat it long enough to kill all the microbes.

Spallanzani's Experiment

Lazzaro Spallanzani, also an Italian scientist, reviewed both Redi's and Needham's data and experimental design and concluded that perhaps Needham's heating of the bottle did not kill everything inside. He constructed his own experiment by placing broth in each of two separate bottles, boiling the broth in both bottles, then sealing one bottle and leaving the other open. Days later, the unsealed bottle was teeming with small living things that he could observe more clearly with the newly invented microscope. The sealed bottle showed no signs of life. This certainly excluded spontaneous generation as a viable theory. Except it was noted by scientists of the day that Spallanzani had deprived the closed bottle of air, and it was thought that air was necessary for spontaneous generation. So although his experiment was successful, a strong rebuttal blunted his claims.

Pasteurization originally was the process of heating foodstuffs to kill harmful microorganisms before human consumption; now ultraviolet light, steam, pressure, and other methods are available to purify foodsin the name of Pasteur.

Pasteur's Experiment

Louis Pasteur, the notable French scientist, accepted the challenge to re-create the experiment and leave the system open to air. He subsequently designed several bottles with S-curved necks that were oriented downward so gravity would prevent access by airborne foreign materials. He placed a nutrient-enriched broth in one of the goose-neck bottles, boiled the broth inside the bottle, and observed no life in the jar for one year. He then broke off the top of the bottle, exposing it more directly to the air, and noted life-forms in the broth within days. He noted that as long as dust and other airborne particles were trapped in the S-shaped neck of the bottle, no life was created until this obstacle was removed. He reasoned that the contamination came from life-forms in the air. Pasteur finally convinced the learned world that even if exposed to air, life did not arise from nonlife.

Excerpted from The Complete Idiot's Guide to Biology © 2004 by Glen E. Moulton, Ed.D.. All rights reserved including the right of reproduction in whole or in part in any form. Used by arrangement with Alpha Books , a member of Penguin Group (USA) Inc.

To order this book direct from the publisher, visit the Penguin USA website or call 1-800-253-6476. You can also purchase this book at Amazon.com and Barnes & Noble .

Origin of Prokaryotes and Eukaryotes: Origin of Prokaryotes

Here are the facts and trivia that people are buzzing about.

The Theory of Biogenesis

What is Biogenesis?

An important theory in biology and molecular genetics, Biogenesis postulates the production of new living organisms from pre-existing life. Read ahead as we explore this seminal theory that changed age-old beliefs.

Biogenesis is based on the theory that life can only come from life, and it refers to any process by which a lifeform can give rise to other lifeforms. For instance, a chicken laying eggs, which hatch and become baby chicken.

Meaning of Biogenesis

The term ‘biogenesis’ comes from ‘bio’ meaning ‘life’, and ‘ genesis’, meaning ‘beginning’. Rudolf Virchow, in 1858, had come up with the hypothesis of biogenesis, but could not experimentally prove it. In 1859, Louis Pasteur set up his demonstrative experiments to prove biogenesis right down to a bacterial level. By 1861, he succeeded in establishing biogenesis as a solid theory rather than a controversial hypothesis.

What Was the Idea of Spontaneous Generation?

The belief in a spontaneous generation is age-old, quite literally. Aristotle in Ancient Greece first pronounces the idea. And consequently, the idea also came to be known as Aristotelian Abiogenesis.

The reason behind the resounding faith in this idea was perhaps the elusive and stealthy nature of the creatures attributed to it, i.e, mice, bacteria, flies, maggots, etc.

The 18th-century path-breaking invention of the microscope that allows most of these creatures, so we can observe them under the microscope and de-mystify their origin. By the time Pasteur set about to do his work in the field, macroscopic biogenesis was already accepted by the scientific community at large. He only had to confirm microscopic biogenesis to prove the hypothesis beyond doubt.

Macroscopic Biogenesis: Francesco Redi’s Experiment

Francesco Redi, as far back as 1668, had set out to refute the idea of macroscopic spontaneous generation, by publishing the results of his experimentation on the matter. Instead of his experiment , Redi had placed some rotting meat in two containers, one with a piece of gauze covering the opening, and the other without it.

He noticed that in the container without the gauze, maggots would grow on the meat itself. However, when he provided the gauze, the maggots would appear on the gauze instead of on the meat. He also observed that flies tend to lay eggs as close to a food source as possible. Thus, he surmised the possibility of macroscopic biogenesis.

Microscopic Biogenesis

Spallanzani’s experiment.

Source: Emaze

He solved this problem by drawing out all the air in the container after sealing it. After experimenting with this manner, he achieved his desired results of a broth that had not clouded with bacterial growth, in line with the theory of biogenesis.

However, his inference was countered by critics who asserted that air was indispensable to support life, therefore the lack of bacterial growth should be attributed to the lack of air, rather than the fact that bacteria spread through contamination. For almost a century since this criticism lay unchallenged.

Pasteur’s Experiment

The caveat of Pasteur’s 1859 experiment was to establish that microbes live suspended in air, and can contaminate food and water, however, the microbes do not simply appear out of thin air. As the primary step to his experiment, Pasteur boiled beef broth in a special flask that had its long neck bent downwards and then upwards.

This interesting contraption ensured the free diffusion of air, and at the same time prevent any bacterial contamination. As long as the apparatus remained upright, the flask remained free of any bacterial growth.

Once we slant the flask, it allows the broth to pass beyond the ‘goose-neck’ bend of the flask’s neck. The broth became clouded with bacterial growth in no time. This path-breaking experiment not only silenced all the criticism based on Spallanzani’s experiment but also cemented the Law of Biogenesis.

Law of Biogenesis Vs. Evolutionary Theory

Scientist fears that the law of biogenesis opposes the theory of evolution. It has surmised that all life stems from inorganic matter from billions of years ago. However, biogenesis simply refutes the theory of spontaneous generation and delves in a matter of generational time-span, and not of what may be achieved over thousands of generations.

While the evolutionary theories take into account the lack of predators, the difference in the chemical composition of the Earth’s atmosphere during the inception of life on Earth, as well as the trial-and-error that had taken place over millions of years to bring us to the stage of life on this planet we witness now, these do not concern the law of biogenesis at all.

Whereas the evolutionary theory demonstrates how life on earth took millions of years of trial-and-error and conducive but very different atmospheric conditions, the theory of spontaneous generation had asserted that complex life could simply appear fully formed in a matter of days. This is the belief that biogenesis had successfully challenged.

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Q. Who Has Propounded the Theory of Spontaneous Generation?

Spallanzani

Ans. C. Aristotle. The idea was first propounded by Aristotle in Ancient Greece. Consequently, the idea came to be known as Aristotelian Abiogenesis.

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Standing next to a table covered by test tubes and beakers, Louis Pasteur holds a bottle partially filled with an unidentified liquid.

Louis Pasteur’s scientific discoveries in the 19th century revolutionized medicine and continue to save the lives of millions today

Regents' Professor of Clinical Laboratory Science, Texas State University

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Rodney E. Rohde has received funding from the American Society of Clinical Pathologists (ASCP), American Society for Clinical Laboratory Science (ASCLS), U.S. Department of Labor (OSHA), and other public and private entities/foundations. Rohde is affiliated with ASCP, ASCLS, ASM, and serves on several scientific advisory boards. See https://rodneyerohde.wp.txstate.edu/service/ .

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Some of the greatest scientific discoveries haven’t resulted in Nobel Prizes.

Louis Pasteur , who lived from 1822 to 1895, is arguably the world’s best-known microbiologist. He is widely credited for the germ theory of disease and for inventing the process of pasteurization – which is named after him – to preserve foods. Remarkably, he also developed the rabies and anthrax vaccines and made major contributions to combating cholera .

But because he died in 1895, six years before the first Nobel Prize was awarded, that prize isn’t on his resume. Had he lived in the era of Nobel Prizes, he would undoubtedly have been deserving of one for his work. Nobel Prizes, which are awarded in various fields, including physiology and medicine , are not given posthumously.

During the current time of ongoing threats from emerging or reemerging infectious diseases, from COVID-19 and polio to monkeypox and rabies , it is awe-inspiring to look back on Pasteur’s legacy. His efforts fundamentally changed how people view infectious diseases and how to fight them via vaccines.

I’ve worked in public health and medical laboratories specializing in viruses and other microbes, while training future medical laboratory scientists . My career started in virology with a front-row seat to rabies detection and surveillance and zoonotic agents, and it rests in large part on Pasteur’s pioneering work in microbiology, immunology and vaccinology.

A black and white illustration of Pasteur with a group of patients.

First, a chemist

In my assessment, Pasteur’s strongest contributions to science are his remarkable achievements in the field of medical microbiology and immunology. However, his story begins with chemistry.

Pasteur studied under the French chemist Jean-Baptiste-André Dumas . During that time, Pasteur became interested in the origins of life and worked in the field of polarized light and crystallography .

In 1848, just months after receiving his doctorate degree, Pasteur was studying the properties of crystals formed in the process of wine-making when he discovered that crystals occur in mirror-image forms , a property known as chirality. This discovery became the foundation of a subdiscipline of chemistry known as stereochemistry , which is the study of the spatial arrangement of atoms within molecules. This chirality, or handedness, of molecules was a “ revolutionary hypothesis ” at the time.

These findings led Pasteur to suspect what would later be proved through molecular biology: All life processes ultimately stem from the precise arrangement of atoms within biological molecules.

Wine and beer – from fermentation to germ theory

Beer and wine were critical to the economy of France and Italy in the 1800s. It was not uncommon during Pasteur’s life for products to spoil and become bitter or dangerous to drink. At the time, the scientific notion of “spontaneous generation” held that life can arise from nonliving matter, which was believed to be the culprit behind wine spoiling.

While many scientists tried to disprove the theory of spontaneous generation, in 1745, English biologist John Turberville Needham believed he had created the perfect experiment favoring spontaneous generation. Most scientists believed that heat killed life, so Needham created an experiment to show that microorganisms could grow on food, even after boiling. After boiling chicken broth, he placed it in a flask, heated it, then sealed it and waited, not realizing that air could make its way back into the flask prior to sealing. After some time, microorganisms grew, and Needham claimed victory.

However, his experiment had two major flaws . For one, the boiling time was not sufficient to kill all microbes. And importantly, his flasks allowed air to flow back in, which enabled microbial contamination.

To settle the scientific battle, the French Academy of Sciences sponsored a contest for the best experiment to prove or disprove spontaneous generation . Pasteur’s response to the contest was a series of experiments, including a prize-winning 1861 essay .

Pasteur deemed one of these experiments as “unassailable and decisive” because, unlike Needham, after he sterilized his cultures, he kept them free from contamination. By using his now famous swan-necked flasks, which had a long S-shaped neck, he allowed air to flow in while at the same time preventing falling particles from reaching the broth during heating. As a result, the flask remained free of growth for an extended period. This showed that if air was not allowed directly into his boiled infusions, then no “living microorganisms would appear, even after months of observation.” However, importantly, if dust was introduced, living microbes appeared.

Through that process, Pasteur not only refuted the theory of spontaneous generation, but he also demonstrated that microorganisms were everywhere. When he showed that food and wine spoiled because of contamination from invisible bacteria rather than from spontaneous generation, the modern germ theory of disease was born .

The origins of vaccination in the 1800s

In the 1860s, when the silk industry was being devastated by two diseases that were infecting silkworms , Pasteur developed a clever process by which to examine silkworm eggs under a microscope and preserve those that were healthy. Much like his efforts with wine, he was able to apply his observations into industry methods, and he became something of a French hero .

Even with failing health from a severe stroke that left him partially paralyzed, Pasteur continued his work. In 1878, he succeeded in identifying and culturing the bacterium that caused the avian disease fowl cholera . He recognized that old bacterial cultures were no longer harmful and that chickens vaccinated with old cultures could survive exposure to wild strains of the bacteria. And his observation that surviving chickens excreted harmful bacteria helped establish an important concept now all too familiar in the age of COVID-19 – asymptomatic “healthy carriers” can still spread germs during outbreaks.

After bird cholera, Pasteur turned to the prevention of anthrax , a widespread plague of cattle and other animals caused by the bacterium Bacillus anthracis . Building on his own work and that of German physician Robert Koch , Pasteur developed the concept of the attenuated, or weakened, versions of microbes for use in vaccines.

In the late 1880s, he showed beyond any doubt that exposing cattle to a weakened form of anthrax vaccine could lead to what is now well known as immunity, dramatically reducing cattle mortality.

A computer-generated image of the rabies virus, colored brown in this illustration and resembling a pinecone.

The rabies vaccine breakthrough

In my professional assessment of Louis Pasteur, the discovery of vaccination against rabies is the most important of all his achievements.

Rabies has been called the “ world’s most diabolical virus ,” spreading from animal to human via a bite .

Working with rabies virus is incredibly dangerous, as mortality approaches 100% once symptoms appear and without vaccination. Through astute observation, Pasteur discovered that drying out the spinal cords of dead rabid rabbits and monkeys resulted in a weakened form of rabies virus. Using that weakened version as a vaccine to gradually expose dogs to the rabies virus, Pasteur showed that he could effectively immunize the dogs against rabies.

Then, in July 1885, Joseph Meister, a 9-year-old boy from France, was severely bitten by a rabid dog. With Joseph facing almost certain death, his mother took him to Paris to see Pasteur because she had heard that he was working to develop a cure for rabies.

Pasteur took on the case, and alongside two physicians, he gave the boy a series of injections over several weeks. Joseph survived and Pasteur shocked the world with a cure for a universally lethal disease. This discovery opened the door to the widespread use of Pasteur’s rabies vaccine around 1885, which dramatically reduced rabies’ deaths in humans and animals .

A Nobel Prize-worthy life

Pasteur once famously said in a lecture , “In the fields of observation, chance favors only the prepared mind.”

Pasteur had a knack for applying his brilliant – and prepared – scientific mind to the most practical dilemmas faced by humankind.

While Louis Pasteur died prior to the initiation of the Nobel Prize, I would argue that his amazing lifetime of discovery and contribution to science in medicine, infectious diseases, vaccination, medical microbiology and immunology place him among the all-time greatest scientists.

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Louis Pasteur’s Contributions to Science

Louis Pasteur in his laboratory, painting by Albert Edelfelt.

Many people know Louis Pasteur for the process that bears his name— pasteurization . However, Pasteur made several other very important contributions to science that you should know about.

Molecular asymmetry In studying crystals of sodium ammonium tartrate, Pasteur found that although they had the same chemical composition, they did not necessarily have the same structure. He noted that the molecules occurred in two mirror-image arrangements that could not be superimposed. This molecular asymmetry, or chirality, is the foundation of a branch of science known as stereochemistry . It had huge implications for how we now understand such things as DNA; the chirality of molecules can even affect how medication is absorbed in the body.
Fermentation In the mid-1850s, Pasteur undertook a series of studies on alcoholic fermentation at a local distillery. He learned about many aspects of fermentation, including the compounds that cause milk to sour. In 1857 he presented evidence that all fermentation is caused by microorganisms and that specific microorganisms cause specific kinds of fermentation.
Pasteurization Using his work with fermentation, Pasteur was able to devise a process, now known as pasteurization , to kill microbes and preserve certain products. Pasteurization prevents fermenting and spoilage in beer, milk, and other goods.
Spontaneous generation Before Pasteur, many prominent scientists believed that life could arise spontaneously . For instance, many people thought that maggots appeared from rotted flesh and that dust created fleas. Pasteur suspected that this was not the case. He disproved spontaneous generation by boiling beef broth in a special flask that deters contamination. When the broth was not exposed to air, it remained sterile and free of microorganisms. When the flask neck was broken and air was allowed to reach the broth, the fluid became cloudy with microbial contamination.
Germ theory Pasteur’s work with microorganisms in fermentation and pasteurization led to a much better understanding of germ theory —that certain diseases result from invasion of the body by microorganisms. Before Pasteur’s time, most people, including scientists, believed that all disease came from inside the body rather than from outside. Pasteur’s findings eventually led to improvements in sterilizing and cleaning in medical practices and antiseptic methods in surgery.
Infectious disease Pasteur successfully identified the organisms that had caused a mysterious disease in silkworms and endangered the French silk industry. He learned how to preserve healthy silkworm moth eggs and prevent contamination by disease-causing organisms. The methods he developed are still used in silk production today. Through his study of silkworms, Pasteur made advances in the field of epidemiology , the study of the distribution of disease as a result of the way host and parasite populations interact.
Vaccines Using his germ theory of disease, Pasteur also made important strides in the field of vaccination . He developed vaccines for chicken cholera and anthrax . Arguably his most important work with vaccines was his development of a rabies vaccine, a new “inactivated” type of vaccine, consisting of a neutralized agent rather than attenuated microorganisms. In 1885 he vaccinated a nine-year-old boy who had been bitten by a rabid dog and helped usher in the practice of preventive medicine.
Virulence Pasteur was the first scientist to recognize that virulence could be increased as well as decreased. This has become extremely important in the study of infectious diseases and their spread, especially epidemics of bovine spongiform encephalopathy ("mad cow" disease) and acquired immunodeficiency syndrome (AIDS), for example.

COMMENTS

Pasteur's Experiment
Pasteur's Experiment
3.1 Spontaneous Generation
Explain the theory of spontaneous generation and why people once accepted it as an explanation for the existence of certain types of organisms; ... Pasteur's experiment consisted of two parts. In the first part, the broth in the flask was boiled to sterilize it. When this broth was cooled, it remained free of contamination.
Louis Pasteur
Louis Pasteur - Microbiology, Germ Theory, Pasteurization
2.1 Spontaneous Generation
Explain how the experiments of Redi and Spallanzani challenged the theory of spontaneous generation. ... Pasteur's experiment consisted of two parts. In the first part, the broth in the flask was boiled to sterilize it. When this broth was cooled, it remained free of contamination. In the second part of the experiment, the flask was boiled ...
1.2 Spontaneous Generation
In this lecture, Pasteur recounted his famous swan-neck flask experiment, stating that "…life is a germ and a germ is life. Never will the doctrine of spontaneous generation recover from the mortal blow of this simple experiment." [4] To Pasteur's credit, it never has. Figure 1.12.
3.1 Spontaneous Generation
In this lecture, Pasteur recounted his famous swan-neck flask experiment, stating that "…life is a germ and a germ is life. Never will the doctrine of spontaneous generation recover from the mortal blow of this simple experiment." [4] To Pasteur's credit, it never has. Figure 3.4.
Louis Pasteur, Spontaneous Generation, and Germ Theory
Prior to Pasteur's experiment, a belief called "spontaneous generation" was a prevalent scientific method to explain how life came to be. This belief outlined that life can essentially arise ...
Pasteur Swan-Neck flask experiment (1861):
Louis Pasteur devised the experiment illustrated above. He heated an infusion sealed in a vessel with a S-shaped or "Swan neck", let it cool, and then broke of the tip of the vessel. This allowed fresh air to enter, but any particulate matter was trapped in the bend of the neck. The culture did not putrefy, even though it had access to air.
Louis Pasteur invented microbiology and transformed public health
Louis Pasteur invented microbiology and transformed ...
Spontaneous Generation
Figure 3. (a) French scientist Louis Pasteur, who definitively refuted the long-disputed theory of spontaneous generation. (b) The unique swan-neck feature of the flasks used in Pasteur's experiment allowed air to enter the flask but prevented the entry of bacterial and fungal spores. (c) Pasteur's experiment consisted of two parts.
Pasteur's Experiment
1 Louis Pasteur designed a procedure to test whether sterile nutrient broth could spontaneously generate microbial life. To do this, he set up two experiments. In both, Pasteur added nutrient broth to flasks, bent the necks of the flasks into S shapes, and then boiled the broth to kill any existing microbes. If left undisturbed, will the broth ...
Origin of Life: Spontaneous Generation
Pasteur's Experiment. Louis Pasteur, the notable French scientist, accepted the challenge to re-create the experiment and leave the system open to air. He subsequently designed several bottles with S-curved necks that were oriented downward so gravity would prevent access by airborne foreign materials. He placed a nutrient-enriched broth in one ...
The Theory of Biogenesis
The Theory of Biogenesis | Spallanzani's and Pasteur's ...
Louis Pasteur's scientific discoveries in the 19th century
Louis Pasteur's scientific discoveries in the 19th century ...
Louis Pasteur's Contributions to Science
However, Pasteur made several other very important contributions to science that you should know about. Molecular asymmetry. In studying crystals of sodium ammonium tartrate, Pasteur found that although they had the same chemical composition, they did not necessarily have the same structure. He noted that the molecules occurred in two mirror ...
Louis Pasteur Biography, Experiments & Inventions
Louis Pasteur Biography, Experiments & Inventions - Lesson

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Pasteur's Experiment

3.1 Spontaneous Generation

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The Theory of Spontaneous Generation

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Disproving Spontaneous Generation

2.1 Spontaneous Generation

The Theory of Spontaneous Generation

Disproving Spontaneous Generation

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3 1.2 Spontaneous Generation

CLINICAL FOCUS: Part 1

The Theory of Spontaneous Generation

Disproving Spontaneous Generation

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Critical Thinking

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3.1 Spontaneous Generation

CLINICAL FOCUS: Part 1

The Theory of Spontaneous Generation

Disproving Spontaneous Generation

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Louis Pasteur, Spontaneous Generation, and Germ Theory

Life Comes From Life

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Louis Pasteur’s scientific discoveries in the 19th century revolutionized medicine and continue to save the lives of millions today

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First, a chemist

Wine and beer – from fermentation to germ theory

The origins of vaccination in the 1800s

The rabies vaccine breakthrough

A Nobel Prize-worthy life

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