redi & pasteur experiments

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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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.

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.

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 ).

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

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?

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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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.

(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. ↵

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Microbe Notes

Experiments in support and against Spontaneous Generation

Spontaneous generation is an obsolete theory which states that living organisms can originate from inanimate objects.
The theory believed that dust created fleas, maggots arose from rotting meat, and bread or wheat left in a dark corner produced mice among others.
Although the idea that living things originate from the non-living may seem ridiculous today, the theory of spontaneous generation was hotly debated for hundreds of years.
During this time, many experiments were conducted to both prove and disprove the theory.

Table of Contents

Interesting Science Videos

Experiments in Support of Spontaneous Generation

The doctrine of spontaneous generation was coherently synthesized by Aristotle, who compiled and expanded the work of earlier natural philosophers and the various ancient explanations for the appearance of organisms, and was taken as scientific fact for two millennia.

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.

John Needham

The English naturalist John Turberville Needham was in support of the theory.
Needham found that large numbers of organisms subsequently developed in prepared infusions of many different substances that had been exposed to intense heat in sealed tubes for 30 minutes.
Assuming that such heat treatment must have killed any previous organisms, Needham explained the presence of the new population on the grounds of spontaneous generation.
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.

Experiments against Spontaneous Generation

Though challenged in the 17th and 18th centuries by the experiments of Francesco Redi and Lazzaro Spallanzani, spontaneous generation was not disproved until the work of Louis Pasteur and John Tyndall in the mid-19th century.

Francesco Redi

The Italian physician and poet Francesco Redi was one of the first to question the spontaneous origin of living things.
Having observed the development of maggots and flies on decaying meat, Redi in 1668 devised a number of experiments, all pointing to the same conclusion: if flies are excluded from rotten meat, maggots do not develop. On meat exposed to air, however, eggs laid by flies develop into maggots.
He tested 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.

Lazzaro Spallanzani

The experiments of Needham appeared irrefutable until the Italian physiologist Lazzaro Spallanzani repeated them and obtained conflicting results.
He published his findings around 1775, claiming that Needham had not heated his tubes long enough, nor had he sealed them in a satisfactory manner.
Although Spallanzani’s results should have been convincing, Needham had the support of the influential French naturalist Buffon; hence, the matter of spontaneous generation remained unresolved.

Louis Pasteur

Louis Pasteur ‘s 1859 experiment is widely seen as having settled the question of spontaneous generation.
He boiled a meat broth in a flask that had a long neck that curved downward, like that of a goose or swan.
The idea was that the bend in the neck prevented falling particles from reaching the broth, while still allowing the free flow of air.
The flask remained free of growth for an extended period. When the flask was turned so that particles could fall down the bends, the broth quickly became clouded.
This work was so conclusive; that biology codified the “Law of Biogenesis,” which states that life only comes from previously existing life.

John Tyndall

Support for Pasteur’s findings came in 1876 from the English physicist John Tyndall, who devised an apparatus to demonstrate that air had the ability to carry particulate matter.
Because such matter in air reflects light when the air is illuminated under special conditions, Tyndall’s apparatus could be used to indicate when air was pure.
Tyndall found that no organisms were produced when pure air was introduced into media capable of supporting the growth of microorganisms.
It was those results, together with Pasteur’s findings, that put an end to the doctrine of spontaneous generation.
Parija S.C. (2012). Textbook of Microbiology & Immunology.(2 ed.). India: Elsevier India.
Sastry A.S. & Bhat S.K. (2016). Essentials of Medical Microbiology. New Delhi : Jaypee Brothers Medical Publishers.
https://study.com/academy/lesson/spontaneous-generation-definition-theory-examples.html
https://www.britannica.com/science/biology#ref498783
https://www.infoplease.com/science/biology/origin-life-spontaneous-generation
https://www.allaboutscience.org/what-is-spontaneous-generation-faq.htm
https://courses.lumenlearning.com/microbiology/chapter/spontaneous-generation/

About Author

Sagar Aryal

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.

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Science News

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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Is Spontaneous Generation Real?

Cell Biology
Weather & Climate
B.A., Biology, Emory University
A.S., Nursing, Chattahoochee Technical College

For several centuries it was believed that living organisms could spontaneously come from nonliving matter. This idea, known as spontaneous generation, is now known to be false. Proponents of at least some aspects of spontaneous generation included well-respected philosophers and scientists such as Aristotle, Rene Descartes, William Harvey, and Isaac Newton . Spontaneous generation was a popular notion due to the fact that it seemed to be consistent with observations that a number of animal organisms would apparently arise from nonliving sources. Spontaneous generation was disproved through the performance of several significant scientific experiments.

Key Takeaways

Spontaneous generation is the idea that living organisms can spontaneously come from nonliving matter.
Over the years great minds like Aristotle and Isaac Newton were proponents of some aspects of spontaneous generation which have all been shown to be false.
Francesco Redi did an experiment with meat and maggots and concluded that maggots do not arise spontaneously from rotting meat.
The Needham and the Spallanzani experiments were additional experiments that were conducted to help disprove spontaneous generation.
The Pasteur experiment was the most famous experiment conducted that disproved spontaneous generation that was accepted by the majority of the scientific community. Pasteur demonstrated that bacteria appearing in broth are not the result of spontaneous generation.

Do Animals Spontaneously Generate?

Prior to the mid-19th century, it was commonly believed that the origin of certain animals was from nonliving sources. Lice were thought to come from dirt or sweat. Worms, salamanders, and frogs were thought to be birthed from the mud. Maggots were derived from rotting meat, aphids and beetles supposedly sprang from wheat, and mice were generated from soiled clothing mixed with wheat grains. While these theories seem quite ludicrous, at the time they were thought to be reasonable explanations for how certain bugs and other animals seemed to appear from no other living matter.

Spontaneous Generation Debate

While a popular theory throughout history, spontaneous generation was not without its critics. Several scientists set out to refute this theory through scientific experimentation. At the same time, other scientists tried to find evidence in support of spontaneous generation. This debate would last for centuries.

Redi Experiment

In 1668, the Italian scientist and physician Francesco Redi set out to disprove the hypothesis that maggots were spontaneously generated from rotting meat. He contended that the maggots were the result of flies laying eggs on exposed meat. In his experiment, Redi placed meat in several jars. Some jars were left uncovered, some were covered with gauze, and some were sealed with a lid. Over time, the meat in the uncovered jars and the jars covered with gauze became infested with maggots. However, the meat in the sealed jars did not have maggots. Since only the meat that was accessible to flies had maggots, Redi concluded that maggots do not spontaneously arise from meat.

Needham Experiment

In 1745, English biologist and priest John Needham set out to demonstrate that microbes, such as bacteria , were the result of spontaneous generation. Thanks to the invention of the microscope in the 1600s and increased improvements to its usage, scientists were able to view microscopic organisms such as fungi , bacteria, and protists. In his experiment, Needham heated chicken broth in a flask in order to kill any living organisms within the broth. He allowed the broth to cool and placed it in a sealed flask. Needham also placed unheated broth in another container. Over time, both the heated broth and unheated broth contained microbes. Needham was convinced that his experiment had proven spontaneous generation in microbes.

Spallanzani Experiment

In 1765, Italian biologist and priest Lazzaro Spallanzani, set out to demonstrate that microbes do not spontaneously generate. He contended that microbes are capable of moving through the air. Spallanzani believed that microbes appeared in Needham's experiment because the broth had been exposed to air after boiling but before the flask had been sealed. Spallanzani devised an experiment where he placed the broth in a flask, sealed the flask, and removed the air from the flask before boiling. The results of his experiment showed that no microbes appeared in the broth as long as it remained in its sealed condition. While it appeared that the results of this experiment had dealt a devastating blow to the idea of spontaneous generation in microbes, Needham argued that it was the removal of air from the flask that made spontaneous generation impossible.

Pasteur Experiment

In 1861, Louis Pasteur presented evidence that would virtually put an end to the debate. He designed an experiment similar to Spallanzani's, however, Pasteur's experiment implemented a way to filter out microorganisms. Pasteur used a flask with a long, curved tube called a swan-necked flask. This flask allowed air to have access to the heated broth while trapping dust containing bacterial spores in the curved neck of the tube. The results of this experiment were that no microbes grew in the broth. When Pasteur tilted the flask on its side allowing the broth access to the curved neck of the tube and then set the flask upright again, the broth became contaminated and bacteria reproduced in the broth. Bacteria also appeared in the broth if the flask was broken near the neck allowing the broth to be exposed to non-filtered air. This experiment demonstrated that bacteria appearing in broth are not the result of spontaneous generation. The majority of the scientific community considered this conclusive evidence against spontaneous generation and proof that living organisms only arise from living organisms.

Microscope, Through the. “Spontaneous Generation Was an Attractive Theory to Many People, but Was Ultimately Disproven.” Through the Microscope Main News , www.microbiologytext.com/5th_ed/book/displayarticle/aid/27.
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Redi experiment (1665)

Origins of Life I: Early ideas and experiments

by David Warmflash, MD, Nathan H Lents, Ph.D.

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Did you know that it is much easier to determine when life appeared on Earth than how life came to exist? Evidence points to life on Earth as early as 3.8 billion years ago, but the question of how life came to be has puzzled scientists and philosophers since prehistoric times. In the 1950s, scientists successfully created biological molecules by recreating the atmosphere of primordial Earth in a bottle and shocking it with lightning. This and other experiments give clues to the origins of life.

Theories about the origins of life are as ancient as human culture. Greek thinkers like Anaximander thought life originated with spontaneous generation, the idea that small organisms are spontaneously generated from nonliving matter.

The theory of spontaneous generation was challenged in the 18th and 19th centuries by scientists conducting experiments on the growth of microorganisms. Louis Pasteur, by conducting experiments that showed exposure to fresh air was the cause of microorganism growth, effectively disproved the spontaneous generation theory.

Abiogenesis, the theory that life evolved from nonliving chemical systems, replaced spontaneous generation as the leading theory for the origin of life.

Haldane and Oparin theorized that a "soup" of organic molecules on ancient Earth was the source of life's building blocks. Experiments by Miller and Urey showed that likely conditions on early Earth could create the needed organic molecules for life to appear.

RNA, and through evolutionary processes, DNA and the diversity of life as we know it, likely formed due to chemical reactions among the organic compounds in the "soup" of early Earth.

The work of Darwin and Wallace went a long way in answering the question of how species evolved over time. The theory of natural selection provided a mechanism by which complex life forms, including humans, could arise from simpler organisms . But that still left open a more difficult question, namely, what is the origin of life itself? It’s one of the most challenging questions in science, even today when we can say confidently when life appeared on Earth.

Microscopic fossils called stromatolites and remains of communities of microorganisms called microbial mats suggest that Earth harbored microorganisms 3.5 billion years ago (Figure 1). Also, the presence of particular carbon isotopes in certain metamorphic rocks in Greenland tell scientists that some kind of life may have been present as much as 3.8 billion years ago. This means that 700 million to one billion years after Earth had formed, life was here. It makes sense, because it corresponds to the time when the planet had reached a cool enough temperature for any life to survive. But honing in on the time when life appeared on this planet still does not tell us how life came to exist.

Stromatolites in the Soeginina Beds of Estonia

Since prehistoric times, people sought mostly spiritual answers to this question. Around campfires during the Stone Age, each budding culture told and retold tales of how the gods created life from some kind of nonliving material, be it mud, clay, rock, or straw. The details of the ancient creation stories changed noticeably over time, but religion was still the mode of thinking by Darwin’s era when it came to the initiation of life itself. Darwin did consider the origin of life and speculated that it had occurred in a warm pond. He suggested that phosphoric salts and ammonia in the pre-biotic pond somehow had been changed chemically by heat , light , and electricity, leading to the synthesis of the organic compounds needed to produce the first living cells . Darwin was not a chemist and this was a very cursory speculation about Earth’s pre-biotic chemistry. It contrasted sharply with the detail and systematic approach of Darwin’s own theory of natural selection .

Even so, the pond idea was a start. Despite living in a society that almost universally assumed Earth had an intelligent creator, scientists in Darwin’s time were already comfortable with and accustomed to considering the possibility of life getting started without intervention from the gods. The idea was called spontaneous generation and, while it was already very well established by Darwin’s time, it dates all the way back to the time of the ancient Greeks.

Early thinkers

About 2,600 years ago, in the Ionian city of Miletus (Figure 2), the natural philosopher Anaximander (c. 610–546 BCE) pondered how human babies were born utterly helpless. Without their parents , young humans had no chance to survive and the state of helplessness continued for years. That reality made for a dilemma when considering the first generation of humans, which, Anaximander assumed, must have begun as infants. To grow up and have their own babies, human ancestors in the very distant past must have been more independent as newborns, Anaximander reasoned. They must have been more like certain other animals whose young are born ready to survive on their own.

Location of Miletus on the western coast of Anatolia

Considering the various animals, Anaximander decided the ancestors of humans had to be fish. Unlike mammals, which needed their mothers to get started in life, fish simply emerge from their eggs and either die or survive. This means that distant human ancestors could survive as infants if they were more like fish than like humans.

Even in Anaximander’s time, people saw skeletons from long-dead creatures. Fossils of extinct life were found long before paleontologists went looking for them. Ancient Greeks lived by the sea, and often the sea washed up skeletons or eroded the ground to expose buried bones. Living in this environment , Anaximander had a general idea of skeletal anatomy and how it was similar and different between humans and other animals. Because of this, he decided that the transition from fish to humans must have been gradual. In other words, humans descended from fish through an evolutionary process .

Since Anaximander proposed no idea of how the apparent evolution from fish to human had taken place, it was not an early form of Darwin’s theory of natural selection . But it was the beginning of thinking that life on Earth began with small organisms . Anaximander’s idea quickly led to the idea that small organisms were generated through a natural process from nonliving matter , such as the mud at the bottom of the sea.

Over the next centuries, Greek thinkers such as Anaximenes (588–524 BCE), Xenophanes (576–480), Empedocles (495–435), Democritus (460–370), and finally Aristotle (384–322) developed and modified the spontaneous generation idea so that it corresponded to what people often observed on land. Farmers leaving grain in an open container noticed that pretty soon mice appeared, as if the grain generated the mice. People leaving meat untended returned to find maggots infesting the meat, as if the meat generated the maggots.

Comprehension Checkpoint

Testing spontaneous generation

By the 18 th and 19 th century, the older Greek idea of spontaneous generation was well ingrained in the minds of everyone who ventured to think that the origin of life might not have required the gods. And living at a time when science was coming to age, some early modern thinkers started treating spontaneous generation less like a philosophy and more like a scientific hypothesis . Gradually, they began subjecting the idea to scientific experimentation.

An early attempt at testing spontaneous generation occurred in the 17 th century, when the Italian scientist Francesco Redi (c. 1626–1697) looked carefully at the meat-maggot phenomenon. After leaving meat in an open jar, he observed that maggots did indeed appear, and that the maggots then developed into flies, which then flew away. However, when he left meat in a sealed jar, the maggots did not appear. Nor did maggots appear when he left the meat in a jar covered with a mesh screen, a precaution he took just in case spontaneous generation required fresh air for some reason. In the terminology of today’s science, we say that the mesh-covered jar “controlled for” the possibility that spontaneous generation required fresh air (Figure 3).

Francesco Redi's spontaneous generation experiment

Since the mesh cover prevented the appearance of maggots, it meant that the maggots were not coming from spontaneous generation , but simply from eggs of adult flies. By the standards of experimental methods in contemporary science, it was a rudimentary experiment , but it was as good as it could be given the equipment available in Redi’s time.

Despite the result of his maggot experiment , Redi still believed that smaller creatures, called “gall insects” came from spontaneous generation . At the same time, a developing invention, the microscope, allowed scientists to focus on creatures even smaller: microorganisms. Using his microscope, an English experimenter, John Needham, noticed that broths made from meat were teeming with microorganisms, so he put spontaneous generation to his own test (see our module Experimentation in Scientific Research ). Needham heated a bottle of broth to kill any microorganisms, and left the bottle for a few days. Then, he looked at the broth under the microscope and found that, despite the earlier heating, the broth contained microorganisms again (Figure 4a).

Needham's spontaneous generation experiment

In Needham’s mind, this finding suggested that the lifeless broth had given rise to life. But another scientist, an Italian named Lazzaro Spallanzani , thought that Needham must have done something wrong. Perhaps, he hadn’t heated the broth to a high enough temperature or for a long enough time. To find out, Spallanzani performed his own experiment . He boiled broth in two bottles, left one bottle open and one closed, and found that new microorganisms appeared only in the open bottle. His conclusion: the microorganisms entered the bottle through the air; they were not generated spontaneously in the broth (Figure 4b).

Experiments seeming to prove or disprove spontaneous generation of life went on for another century. Because of the difference between closed and open vessels, arguments focused on the possibility that spontaneous generation of life might require fresh air. Thus, lack of air in Spallanzani’s closed bottle could have been a factor confusing the results. This possibility attracted the attention of the 19 th century’s most famous microbiologist: Darwin’s contemporary, Louis Pasteur .

Pasteur was drawn to the issue, but once involved he knew he that needed to control for the possibility that air was needed to generate life from nonliving matter . To do this, he designed flasks with long, specially curved, swanlike necks. This allowed sterilized broth to be exposed to fresh air from the outside, but any microorganisms from the air would be trapped in a pool of water in the neck. (See our module Experimentation in Scientific Research for more information on designing experiments .)

The sterilized broths in Pasteur’s special flasks did not become infested with microorganisms despite being exposed to fresh air (Figure 5). And so, after a run of more than 24 centuries, the hypothesis of spontaneous generation was finally laid to rest.

Pasteur's flask with long, swan-like necks

This meant that scientists no longer thought that microorganisms, or small animals, could suddenly emerge with no parents , but it didn’t stop people from thinking about life coming from nonliving matter . Pasteur’s publication of his experimental results disproving spontaneous generation of microorganisms came in the very same year as Darwin’s Origin of Species . This made for paradox. Around the world, scientists were fairly certain that evolution really happened, that all modern species came ultimately from pre-existing, living forms. However, as for the question of how life started in the first place, scientists had just disproved the only explanation they had.

Darwin’s pond idea was completely speculative. There was no way to test it the way he tested natural selection through years of observation of numerous species . And so, when it came to the initiation of life itself, scientists of Darwin’s era were stumped. All they could do was to throw up their hands, or chalk it up to the creation stories of their religions.

Old and new ideas

In addition to spontaneous generation , the ancient Greeks produced another idea for the origin of life on Earth: panspermia . An Ionian Greek named Anaxagoras (510–428 BCE) thought that life arrived on Earth as seedlings that came through space from other worlds. Often people think of panspermia as an alternative to the idea of life emerging from nonliving matter , but it’s actually not. Instead, panspermia only moves the origin of life off the Earth to another planet or moon, and further back in time. Thus, after Pasteur’s disproval of spontaneous generation , the motivation was stronger than ever to determine how life got started.

By the late 19th century, English biologist Thomas Henry Huxley (1825–1895) coined the term abiogenesis to describe life forms emerging from non-living chemical systems . On first hearing the term, it may sound as if abiogenesis is merely a more modern take on spontaneous generation , but there is a major difference. With spontaneous generation , the idea was that certain materials, be it meat, grain, or mud, were capable of constantly producing some kind of creature. What Huxley had in mind was the chemical reactions of life slowly emerging on the early Earth over a long period of time. Huxley knew that the mixture would have to be more complex than Darwin’s ammonia and phosphoric salts , but he did not attempt to work out the details. Somehow, though, he thought an optimal mixture of simple chemicals generated the complex chemicals needed for life, such as enzymes , and the earliest living cells .

Abiogenesis

As for how abiogenesis could occur on the primordial Earth, serious thinking about this began in the 1920s with two scientists working entirely independently of one another.

In 1922, Aleksandr Oparin, a Russian biochemist, gave a lecture on the origins of life, which was published as a booklet in 1924. For several years, the booklet was not translated from Oparin’s native Russian, so his ideas were unknown outside of the USSR. Meanwhile, British biochemist John Burdon Sanderson Haldane (usually known by his initials JBS Haldane) was working on similar ideas. Unlike his Russian counterpart, Haldane and his work were extremely visible. He was a great popularizer of science, doing for the early 20th century what astronomer Carl Sagan did later, making science understandable and fascinating for the masses. Haldane’s hands were in numerous areas of life science. He was the author of dozens of scientific papers and spent a great deal of time explaining his work and its importance to people outside the scientific world.

In connection with other questions of biology, Haldane was working with enzymes , which he thought were on the border between living and nonliving chemistry. Consequently, he hypothesized that abiogenesis took place through a complex mechanism involving enzymes and viruses. By Haldane’s time, scientists figured out that the atmosphere of the primordial Earth had been a reduced atmosphere. This means that it contained reduced carbon chemical compounds , such as methane, in contrast to oxidized chemical compounds, such as carbon dioxide (which could be present, but in much lower quantities compared with methane). It also contained hydrogen, ammonia, some water vapor, and, importantly, no oxygen.

Oxygen can come only from organisms that carry out photosynthesis to make their own food. Such organisms are called autotrophs. Haldane reasoned that the first cells must have been heterotrophs, organisms that take their food from the surrounding environment . Methane is a gas , but other simple, organic compounds made from it are liquid and would have rained down on the early Earth. They accumulated as pools of liquid on the surface , forming a kind of organic broth that became known as “Haldane’s soup” (Figure 6).

Grand Prismatic Spring in Yellowstone National Park

Because there was no oxygen in the atmosphere , the early Earth lacked a layer of ozone to block out powerful ultraviolet radiation from space. Haldane hypothesized that the ultraviolet radiation from space, along with lightning constantly hitting the primordial organic soup, delivered energy to the various simple organic compounds . This caused chemical bonds between the atoms of the molecules to break and reform, creating new and different molecules, leading to extremely large, complex organic molecules . Haldane speculated that this happened over millions of years, until finally a molecule arose that could copy itself crudely using other molecules in the “soup” as building blocks.

Molecules that could copy better than their neighbors multiplied and gradually dominated the soup. Some of these self-copying molecules became surrounded by a kind of barrier, the precursor to what we call a membrane . This happened by accident, so it was very rare, but when it did happen, Haldane explained, the enclosed, self-copying molecules had an enormous survival advantage. So they came to dominate, ate up the soup, and life had begun.

Haldane’s idea was purely hypothetical. No one tested it yet, but it was far more elaborate than Darwin’s phosphoric salt idea. Moreover, it was perfectly consistent with the state of science in the 1920s and 30s regarding the chemistry of the early Earth. Then, in 1936, Oparin’s work was finally translated from Russian. It turned out that he was proposing almost the same thing as Haldane, so the idea became known as the Oparin-Haldane hypothesis .

Putting ancient Earth into the lab

As for testing the Oparin-Haldane hypothesis , that role fell into the hands of a graduate student, Stanley Miller. In the early 1950s, Miller was looking for a thesis project in the Department of Chemistry at the University of Chicago. In 1952, his academic mentor, Professor and Nobel laureate Harold Urey, suggested that he try putting the origins of living molecules to a test. That meant recreating the kind of atmosphere that scientists thought had existed on primordial Earth: hydrogen, methane, ammonia, and water. It also meant providing what Haldane thought set the stage for creating more complicated molecules needed for life: lightning and ultraviolet light .

Once the ancient atmosphere was created and contained in a flask, Miller and Urey exposed the mixture to powerful ultraviolet light . They also put electrodes inside the flask and sent an electric current through the apparatus, creating sparks to simulate lightning, which interacted with the gases in the flask. After several days, they checked the contents of the liquid that accumulated at the bottom of the apparatus (Figure 7). They found that different molecules had been created, including various important biological molecules, such as the amino acids glycine, alanine, and valine. They ran the experiment over and over and, depending on how they changed around the gas mixture, different varieties of amino acids and other biological molecules were created. This showed that it was possible for biologically important molecules to form on a planet under abiotic conditions.

Over the years, as Miller progressed through his career, scientists studying planetary atmospheres and the ancient Earth had second thoughts about Earth’s primordial atmosphere. Perhaps it had not been dominated by methane, hydrogen, and ammonia, and possibly it could have been more oxidized as opposed to reduced. But as theories about the ancient atmosphere were refined, Miller tried variations of his original experiment with the adjusted gas mixtures . Although chemical products changed with each new mixture, in each case they included compounds that were vital to life, such as amino acids , or nitrogenous bases , the building blocks needed to make DNA and RNA . The emerging answer seemed to be that, almost regardless what the precise mixture and conditions were, complex organic molecules would result.

After the Miller-Urey experiment: Exploring proteins and membranes

While ideas about Earth’s primordial atmosphere were in flux from the 1970s onward, NASA’s exploration of the outer Solar System revealed some amazing things about the moons orbiting Jupiter and Saturn. In particular, the space probes Voyager 1 , Voyager 2 , and Cassini and an atmospheric entry probe to Saturn’s moon Titan called the Huygens probe revealed the exact makeup of Titan’s atmosphere. This inspired other scientists, such as Carl Sagan , to redo Miller’s 1952 experiment with a Titan atmospheric mixture. This too produced important biological compounds . Thus, today, the moon Titan is a prime focus for astrobiology studies in the Solar System. It may have exotic life forms, or it may be a model of how Earth was prior to life.

Several years after the original Miller-Urey experiment , another investigator, Sidney Fox, ran experiments showing that some of the Miller-Urey compounds – the amino acids – could join together to form polymers , bigger molecules known as peptides , or small proteins . This happened when amino acids made through a Miller-Urey mechanism were splashed onto surfaces of clays and other materials, under hot, dry conditions. On the ancient Earth, such conditions would have occurred at the boundary between ancient ponds or seas and ancient land. Given enough time, complex proteins could arise.

Other researchers later found that spheres of lipids (the class of organic molecules that includes fats) also could form under conditions thought to exist on the ancient Earth. This would create a water environment inside the sphere that was separated from the outside. In other words, crude membranes can form spontaneously under the same conditions in which biological compounds like amino acids and small proteins can form. The fact that membranes can form spontaneously is key to origins of life research . This is because to move from non-living chemistry to biology, very complex networks of chemical reactions need to emerge. Like a car being made on an assembly line, biological molecules are put together section by section. They also are converted into different molecules section by section, so there is a series of intermediate chemicals in addition to a starting molecule (called a substrate) and final product of each reaction .

In an open environment like Haldane’s primordial soup, or in an ocean, the various intermediates would simply diffuse away before the chemical pathway had a chance to evolve. But a membrane would enclose all of the chemicals within a compartment. That compartment would then act as a chemical laboratory, holding inside any reactions that happened to emerge. Since we know that membrane spheres can spontaneously form, the primordial soup of early Earth must have had billions of these little chemical laboratories in which the chemistry of life was sputtering along.

Moving to a DNA world

Demonstration that biological molecules and membranes can arise in an abiotic environment is not a demonstration of the emergence of life. It shows only what might have happened in the transition from non-living chemistry to the eventual formation of life. It does, however, show that a necessary step in abiogenesis – the spontaneous emergence of complex organic molecules – is not only possible, but likely under the right conditions.

Theoretically, continuous rearrangement and construction of larger and larger organic molecules from chemical building blocks that would form on the early Earth should eventually lead to molecules that can copy themselves. That’s because the bigger an organic molecule gets, the more functional chemical groups it has. Functional groups are sections of molecules with atoms other than carbon, such as oxygen, nitrogen, and phosphorus, which like to hold onto electrons . This allows for electrons to be moved around between parts of the molecule and between the molecule and other molecules. Also, the bigger a molecule gets, the more it’s able to bend and twist around. This capability, together with the capability to move around a lot of electrons, &^means it’s possible, simply by luck, for any random, very large organic molecule with a lot of nitrogen, oxygen, and phosphorus atoms to have some enzymatic capability –that is, to be able to catalyze chemical reactions .

Certain sets of reactions catalyzed by a molecule can result in the molecule making a copy of itself. Thus, with plenty of building materials in a Haldane soup, as time goes on, it is likely that self-replicating molecules would emerge. The first self-replicating molecule would have only crude copying ability. But, since it would not copy itself exactly, each new “copy” would be a little different than the “parent” molecule. Randomly, a newly copied molecule might have the ability to copy slightly better than the molecule that made it. Natural selection would then work for non-living chemical molecules similar to how Darwin described it working for living organisms . Those molecules copying better would make more copies using building blocks taken from the breakdown of other molecules that could not copy themselves so well.

Self-copying molecules enclosed in membranes would fare even better because they would be held close together with other chemicals. But for life to really begin, there has to have been a molecule whose copying ability was extremely good. Today, there is such a molecule: DNA . However, DNA is incredibly complex and this makes for a chicken and egg kind of dilemma.

In the 1980s, scientists began to realize that not all enzymes are proteins . Scientists dissected some cell components called ribosomes and found that they are made of protein and RNA . What was strange was that some of the RNA molecules actually work as enzymes. They can catalyze chemical changes in themselves and in other RNA molecules.

Like DNA , RNA can hold genetic information, but RNA is less complex than DNA (Figure 8). Consequently, a hypothesis called the “RNA world” was proposed independently by three different researchers: Leslie Orgel, Francis Crick , and Carl Woese. It’s a keystone in origins of life research today. The idea is that RNA emerged on Earth prior to DNA and was the genetic material in the first cells (or in the first cells on a different world, if life began somewhere else).

Today, no known bacterial cell or other fully-fledged life form uses RNA the way that we use DNA , as the storage molecule for genetic information. But there are RNA viruses. Not all viruses are RNA viruses; some use DNA to hold genetic instructions, just as our cells do. But if RNA is adequate as the only genetic material in some viruses, it’s easy to imagine RNA also being the only genetic material in an early bacterium, or other singled-celled creature that could have existed on the early Earth.

It’s not hard to image how the transition from RNA to DNA might have occurred. As with the evolution of everything else, there would have been mistakes. In living organisms today, DNA stores genetic information over the long term and DNA sequences are transcribed into RNA sequences, which then are used to put together sequences of amino acids into proteins (see our Gene Expression: An overview module). Essentially, DNA is an additional layer beyond RNA and the proteins that RNA makes. RNA sequences could have been the genes before a mistake created DNA. Being more stable chemically than RNA, DNA took over the job of storing genetic information. This gave RNA a chance to get better at translating genetic information into proteins.

That would have been an enormous step in life’s evolution . It also would mean that life was not here all at once. Rather, abiogenesis occurred in increments or steps during prebiotic, chemical evolution. Thus, entities must have existed along a spectrum from nonliving to living, just as viruses today have characteristics of both living and nonliving entities. We don’t know the precise abiogenesis pathway, but scientists have worked out each of the major steps necessary to go from nonliving chemistry to self-sustaining cells . Importantly, scientists also have conducted laboratory experiments demonstrating that each step is possible. Unlike the days of Anaximander , Darwin, or even Haldane, there are no big holes or theoretical barriers to abiogenesis. Scientists have a good idea of how it probably happened. Still, in terms of the details within each major step, that is where science is now focused on getting some answers.

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How the Scientific Method Works

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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.

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Pasteur Brewing Louis Pasteur – Science, Health, and Brewing

Louis pasteur, francesco redi, and spontaneous generation for kids.

Where do cells come from? If a cut of meat is let out, over time it will putrefy and begin to teem with microorganisms and possibly with larger organisms like maggots. Prior to the mid-to-late 19th century, the origin of microorganisms in decaying matter was in question. Some maintained that microbes arose from other microbes that landed on the food from the air. Other supported the hypothesis of spontaneous generation, which states that living organisms can arise spontaneously from nonliving matter.

Redi’s Experiment

In the 1600’s, Francesco Redi sought to test the hypothesis of spontaneous generation by applying what came to be known as the scientific method–a process of making observations, asking questions, formulating a hypothesis and designing experiments to test the hypotheses.

Redi and others observed that flies and then maggots could be seen around pieces of meat that were left out in the open. He therefore asked the following questions: Where do flies come from? Is the rotting meat transformed into the flies? From these questions, Redi formulated the hypothesis that only flies can make flies, and that rotting meat cannot be transformed into flies.

Redi sought to test his hypothesis by performing the following experiment. He placed pieces of meat into three glass jars. The first jar was left open, the second was covered with a loos netting, and the third was completely sealed. All jars were exposed to flies in the surrounding room. Redi predicted that if meat could not be transformed into flies, then the sealed containers should not produce either maggots or flies. Whereas if the meat can be so transformed, then the sealed jar should also develop maggots and flies.

Redi recorded the presence or absence of flies and maggots in each of the three types of jars. As he predicted, neither flies nor maggots were found in the sealed jars, whereas in the open jars, maggots and flies were abundant. In the jars covered with netting, maggots were found within the netting itself, but not on the meat inside the jar. Redi concluded that meat could not transform into flies, only flies could produce flies. The theory of spontaneous generation could not be supported and was therefore incorrect.

Pasteur’s Experiment

Unfortunately, Redi’s experiment did not convince everyone. Some argued that while spontaneous generation might not apply to larger organisms like maggots and flies, it might still be applicable to smaller microbes. The question was finally answered definitively in the late 1800s by Louis Pasteur, in his now classic experiment.

Pasteur’s hypothesis was that if cells could arise from nonliving substances, then they should appear spontaneously in sterile broth.

To test his hypothesis, he created two treatment groups: a broth that was exposed to a source of microbial cells, and a broth that was not. For his control treatment, Pasteur used a straight-necked flask that allowed particles in the air to fall into the broth stored in the flask. For his experimental treatment, Pasteur used a swan-necked flask. The neck shaped and length assured that no cells could enter the broth from the air.

Swan Necked Flasks from Pasteur's Laboratory

By changing a single variable–the shape of the flask neck–Pasteur was able to conclude that cells were not generated spontaneously but were actually entering the broth from the surrounding air. Microorganisms, carried by dust particles, fell into the straight-necked flask. However, the swan neck trapped the particles, preventing cells from entering the broth.

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The Experiments of Redi and Pasteur Helped to Demonstrate That
Louis Pasteur, Francesco Redi, and Spontaneous Generation for Kids
Origem da vida Redi e Pasteur
Experimento de Redi e o fim da abiogênese
The Experiments of Redi and Pasteur Helped to Demonstrate That
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3.1 Spontaneous Generation
Figure 3.4 (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.
3.1 Spontaneous Generation
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."
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 ...
Experiments in support and against Spontaneous Generation
Though challenged in the 17th and 18th centuries by the experiments of Francesco Redi and Lazzaro Spallanzani, spontaneous generation was not disproved until the work of Louis Pasteur and John Tyndall in the mid-19th century. ... Louis Pasteur. Louis Pasteur's 1859 experiment is widely seen as having settled the question of spontaneous ...
Origin of Life: Spontaneous Generation
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. ... Pasteur's Experiment. Louis Pasteur, the notable French ...
Louis Pasteur invented microbiology and transformed public health
Demonstrations by the 17th century Italian scientist Francesco Redi challenged that belief, ... but it was Pasteur's series of experiments that isolated the responsible microorganism, verifying ...
Spontaneous Generation vs. Biogenesis SCIENTIFIC Classic Experiments by
• Redi continued his experiment by placing living or dead flies in sealed jars and noting the outcome. • Decrease the time for growth in Pasteur's experiment by placing the end of the plastic tubing into the nutrient broth. • Pasteur also proved that microorganisms cannot travel long distances without the assistance of air current or ...
Is Spontaneous Generation Real?
The Pasteur experiment was the most famous experiment conducted that disproved spontaneous generation that was accepted by the majority of the scientific community. Pasteur demonstrated that bacteria appearing in broth are not the result of spontaneous generation. ... In his experiment, Redi placed meat in several jars. Some jars were left ...
Redi experiment
Redi experiment (1665) As late as the 17th century, some biologists thought that some simpler forms of life were generated by spontaneous generation from inanimate matter. Although this was rejected for more complex forms such as mice, which were observed to be born from mother mice after they copulated with father mice, there remained doubt for such things as insects whose reproductive cycle ...
Origins of Life I
Since prehistoric times, people have pondered how life came to exist. This module describes investigations into the origins of life through history, including Louis Pasteur's experiments that disproved the long-held idea of spontaneous generation and and later research showing that the emergence of biological molecules from a nonliving environment - or abiogenesis - is not only possible ...
Francesco Redi
Francesco Redi was born in Tuscany, Italy on February 18, 1626. In 1647, at the age of 21, Redi graduated with his doctoral degree in medicine and philosophy from the University of Pisa. After ...
Life Science B
What was the control in Pasteur's experiment? a straight neck flask to allow air to get in. What was the variable in Pasteur's experiment? a swan neck flask that prevented air from getting in. What did Redi find in his experiment? Flies were not found in the sealed jars of rotting meat.
Redi/ Pasteur experiment Flashcards
what was Pasteur's experiment trying to prove. disprove the idea that microorganisms arise spontaneously from vital force in the air. what did pasteur's experiment look like. what was the iv in pasteur's experiment. exposure of broth to dust particles. what was the dv in pasteur's experiment. microorganism growth.
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 ...
Francesco Redi and Spontaneous Generation
http://www.pasteurbrewing.comSimilar to Louis Pasteur's spontaneous generation experiment, the 17th century Italian scientist Franceso Redi conducted an expe...
Francesco Redi and Spontaneous Generation
The theory of Spontaneous Generation proposed that life or living organisms could be "spontaneously generated" from non living matter. Similar to Louis Pasteur's spontaneous generation experiment, the 17th century Italian scientist Franceso Redi conducted an experiment to refute the theory of Spontaneous Generation nearly 200 years earlier.
Louis Pasteur, Francesco Redi, and Spontaneous Generation for Kids
Redi's Experiment. In the 1600's, Francesco Redi sought to test the hypothesis of spontaneous generation by applying what came to be known as the scientific method-a process of making observations, asking questions, formulating a hypothesis and designing experiments to test the hypotheses. Redi and others observed that flies and then ...

3.1 Spontaneous Generation

Clinical Focus

The Theory of Spontaneous Generation

Check Your Understanding

Disproving Spontaneous Generation

3.1 Spontaneous Generation

CLINICAL FOCUS: Part 1

The Theory of Spontaneous Generation

Disproving Spontaneous Generation

Multiple Choice

Critical Thinking

Media Attributions

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2.1 Spontaneous Generation

The Theory of Spontaneous Generation

Disproving Spontaneous Generation

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Experiments in support and against Spontaneous Generation

Experiments in Support of Spontaneous Generation

John Needham

Experiments against Spontaneous Generation

Francesco Redi

Lazzaro Spallanzani

Louis Pasteur

John Tyndall

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Origin of Life: Spontaneous Generation

Origin of Life

Redi's Experiment and Needham's Rebuttal

Spallanzani's Experiment

Pasteur's Experiment

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Is Spontaneous Generation Real?

Key Takeaways

Do Animals Spontaneously Generate?

Spontaneous Generation Debate

Redi Experiment

Needham Experiment

Spallanzani Experiment

Pasteur Experiment

Origins of Life I: Early ideas and experiments

Comprehension Checkpoint

How the Scientific Method Works

Pasteur's Experiment

Pasteur Brewing Louis Pasteur – Science, Health, and Brewing

Redi’s Experiment

Pasteur’s Experiment

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