hypothesis of spontaneous generation redi

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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• Location: Houston, Texas
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3 1.2 Spontaneous Generation

Learning objectives.

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

CLINICAL FOCUS: Part 1

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 (“vital heat”). As evidence, he noted several instances of the appearance of animals from environments previously devoid of such animals, such as the seemingly sudden appearance of fish in a new puddle of water. [1]

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

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

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 1.11 ).

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

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?

Key Takeaways

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

Multiple Choice

Fill in the blank, short answer.

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

Critical Thinking

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

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

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3. The Cell

3.1 Spontaneous Generation

Learning objectives.

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

CLINICAL FOCUS: Part 1

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 (“vital heat”). As evidence, he noted several instances of the appearance of animals from environments previously devoid of such animals, such as the seemingly sudden appearance of fish in a new puddle of water. [1]

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

However, one of van Helmont’s contemporaries, Italian physician Francesco Redi (1626–1697), performed an experiment in 1668 that was one of the first to refute the idea that maggots (the larvae of flies) spontaneously generate on meat left out in the open air. He predicted that preventing flies from having direct contact with the meat would also prevent the appearance of maggots. Redi left meat in each of six containers ( Figure 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 2 ).

• 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?

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. ↵

Microbiology: Canadian Edition Copyright © 2019 by Wendy Keenleyside is licensed under a Creative Commons Attribution 4.0 International License , except where otherwise noted.

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Redi experiment (1665)

Spontaneous Generation

Learning objectives.

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

Clinical Focus: Anika, Part 1

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

• What types of respiratory disease may be responsible?

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

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 (“vital heat”). As evidence, he noted several instances of the appearance of animals from environments previously devoid of such animals, such as the seemingly sudden appearance of fish in a new puddle of water. [1]

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

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

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

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

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).

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

Think about It

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

Disproving Spontaneous Generation

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

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

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

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

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

Key Concepts and Summary

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

Multiple Choice

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

• Francesco Redi
• Louis Pasteur
• John Needham
• Lazzaro Spallanzani

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

• Jan Baptista van Helmont

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

• Antonie van Leeuwenhoek

Fill in the Blank

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

Exposure to air is necessary for microbial growth.

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

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Francesco Redi and Controlled Experiments

Most people can name one 17th century Italian scientist who challenged Aristotle's writings and changed the way science was done for centuries to come. There were actually two! Galileo was one. Francesco Redi was the other. Francesco Redi is known for his early use of controlled experiments and his challenge to the theory of spontaneous generation.

Controlled Experiments

When a scientist designs an experiment it is important to eliminate as many unknowns as possible. For instance, if one were trying to assess the health effects of a drug on humans, there are many factors which may affect health..simply counting how many of the patients get better or worse when given the drug is not good enough. We want to know how many got better or worse specifically from the drug. One solution might be to introduce a control to compare the drug-based tests against some standard case. In these drug-tests one group is commonly given the drug and another group, the control group, is given a placebo (commonly a sugar-pill with no known health effects). The subjects do not know which type of pill they have been given. The drug results from the test group can then be compared against those of the control group and we can get a better idea of which effects result from the drug. This important advance in scientific methods was introduced only 25 years after the death of Galileo and only a few kilometres away from where he lived.

The Francesco Redi Experiment

Francesco Redi was able to disprove the theory that maggots could be spontaneously generated from meat using a controlled experiment. Spontaneous generation, the theory that life forms can be generated from inanimate objects, had been around since at least the time of Aristotle. Francesco took two sets of four jars. In one set he placed different types of meat and fish into the different jars but left the jars open. In the other set he placed the same types of meat and fish into the jars but securely sealed the tops with paper and string. Maggots developed in the open jars but did not develop in the paper-sealed jars. The diagram below shows one pair of jars. Redi repeated this experiment and got the same results. Redi realized that some may criticize the experiment because one set of jars was open to the air and the other was sealed, potentially affecting the results. Redi followed the original set of trials with one where he placed flesh and fish into a large vessel and sealed it with fine gauze instead of paper. This would allow air to enter and leave the vessel. The maggots did not form in the vessel [_1_] .

Today controlled experiments are commonly demanded by scientific journals and are sometimes legally required by regulatory bodies (especially for pharmaceuticals).

We are taught that Galileo introduced the scientific method while Francesco Redi introduced the controlled experiment. Both beliefs are simplistic. Francesco Redi and Galileo Galilei demonstrated their methods using very simple experiments then explained their procedures in clear and compelling ways. This is why both are so important. But scientists before Redi and Galileo had recognized the need to control variables and had described the sequence of steps described in Galileo's experimental method. When Galileo was still a young boy and Redi was yet to be born, Giuseppe Moletti, a professor at the University of Padua, conducted a series of experiments on free fall by dropping weights in different media (see Timeline of Classical Mechanics ). His test with free fall in water and air specified that the balls must be of the same substance, weight and figure in order to remove doubt. In the same book, when Moletti described dropping balls of wood and lead from a tower to demonstrate that free fall doesn't depend on weight (as Aristotle had said) he was careful to eliminate size as a nuisance variable by conducting the experiment with wooden balls of different sizes [_2_] .

Controlling for known variables doesn't guarantee that you will get correct results. That is because "you don't know what you don't know". There might be variables that need to be controlled that you don't even know exist. This is why the famous Tower of Pisa experiment actually came up with incorrect results. The Tower of Pisa experiment did occur even though it considered a myth (see Myth 1. The Tower of Pisa Myth ). It was conducted by Vincenzio Renieri, a Catholic monk, and not by Galileo as is commonly thought. Like Moletti before him, Renieri, controlled for size when he dropped two balls of the same size (one of wood and one of lead). He came up with the wrong results. There was almost 2 metres difference between the heavier and lighter balls when they hit the ground. Galileo described similar results in some of his works. These scientists could not have known that they needed to control for human physiology as well. Modern experiments with humans dropping balls of different weights show that there is a tendency to grip the heavier ball more tightly and release it more slowly [_3_] .

Francesco Redi and Galileo Galilei

There are many parallels between Francesco Redi and Galileo Galilei. Both were radical thinkers that challenged Aristotelian thought. It was Aristotle who proposed life-forms such as maggots spontaneously generated, and it was Redi who proved this false. Both wrote in Italian instead of Latin. Both graduated from the University of Pisa and went on to be associated with the court of the Medicis. Both are associated with advances in scientific methods.

There was one big difference between the two. Galileo had a major clash with the church later in life ( the Galileo Affair ) and Francesco died without encountering any major dispute with the church. This is odd. Francesco Redi was defending scientific ideas that were as radical as Galileo's yet his experience was completely different. Could Galileo's personality and his personal and professional disagreements with the other scientists of the day explain the difference? And leaving personality aside, could the difference be that Francesco Redi provided better arguments than did Galileo ( see Galileo and Heliocentricity ).

Copyright Joseph Sant (2019).

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Sant, Joseph (2019).Francesco Redi and Controlled Experiments. Retrieved from http://www.scientus.org/Redi-Galileo.html

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<a href="http://www.scientus.org/Redi-Galileo.html">Francesco Redi and Controlled Experiments</a>

Born: Feb. 18, 1626, Arezzo, Italy

Died: March 1, 1697, Pisa,Italy

Important Dates

1664 Redi's work,"Observations on Vipers" , dismisses several myths about poisonous snakes.

1668 "Experiments on the Generation of Insects" published. This reported on Redi's controlled experiments with insects that called into question the validity of "spontaneous generation".

1685 "Bacco in Toscana", a collection of Redi's poems is published.

Spontaneous Generation Theory

Table of Contents

Aristotle’s Work

Early experiments, franceso redi, pier antonio micheli, john needham, lazzaro spallanzani, disproving the theory, louis pasteur, john tyndall, frequently asked questions.

Spontaneous generation theory is an archaic scientific theory which stated that living organisms could arise from nonliving matter and that such a process was regular in nature. It also explained the origin of life from the nonliving subjects. According to that theory, a piece of bread and cheese wrapped and left in a corner could give rise to mice in a few weeks, or maggots could rise from dead flesh.

The hypothesis was designed by Aristotle on the basis of previous work of natural philosophers and the theory held its place for two millenniums. Francesco Redi and Lazzaro Spallanzani then challenged this theory in the 17th and 18th centuries, but it was still not discredited. It was not until the work of Louis Pasteur and John Tyndall in the 19th century that this theory was finally disproved.

The theory lines up with the theory of origin of life, which states the process of abiogenesis. Abiogenesis is the natural process of creation of simple organic compounds from nonliving matter. The term equivocal generation, also called heterogenesis, describes the theory of spontaneous generation. According to equivocal generation, one life arises from another unrelated life form.

According to Aristotle, every living being is made up of a compound of matter and form. In his sexual theory of reproduction, he stated that male’s semen was efficient cause that passed down characteristics to female matter (menstrual blood), and gave rise to its offspring. He believed that the male semen and female matter were refinements that were produced by bodies as a result of their proportions of heat, ingested food and were a byproduct of the elements earth and water. Yet, he believed that creatures arose from spontaneous generation and not sexual reproduction.

Analogous to his sexual reproduction theory, he said that non living matter just like seminal fluid had ‘pneuma’ or ‘vital heat’ that endowed the subtances with vital properties. He came to the conclusion that whether a life form arose from sexual reproduction or spontaneous generation, they were a result of interaction between vital heat and elemental matter.

Franceso Redi was an Italian naturalist who challenged the ancient belief of spontaneous generation of maggots on decaying meat in 1668. He believed that maggots could be prevented if flies were not allowed direct contact with the meat. He designed an experiment where he put pieces of meat in six different containers. He covered two of them with gauze, two tightly sealed with corks and left the remaining two open in the air. His hypothesis came true as it was observed that there were no maggots in the covered (with gauze and cork) containers but maggots were observed in the open container. He came to the conclusion that flies were able to lay their eggs on the open piece of meat and that the maggots were their offspring who grew on flesh.

Pier Antonio Micheli, an Italian botanist, performed another experiment in 1729 where he placed fungal spores on a slice of melon and observed that the same was produced on the melon slice. He concluded that the new spores definitely did not arise from spontaneous generation.

John Needham, an English biologist, did yet another experiment in 1745 with boiled broths. He infused a broth by mixing plant and animal matter and boiled it in the belief that it would kill all the microorganisms . He sealed the broth and left it for a few days. He observed that the broth had become cloudy and that it has microscopic organisms in it. He reiterated the spontaneous generation theory and many of his peers believed him. However, in reality, the broth was not boiled vigorously so as to kill all the microorganisms.

Lazzaro Spallanzani, an Italian biologist, reattempted Needham’s experiment in 1768. He took animal and plant matter-infused broths and boiled them vigorously. He kept one of the jars sealed and left the other one open to the air. According to his observations, the sealed jar was clear and did not have any growth. He then concluded that air was the force that was introducing microbes into the flask.

By this time, there was increased skepticism among scientists about the spontaneous generation theory.

In 1859, Louis Pasteur, a French microbiologist conducted another broth experiment that settled the question of spontaneous generation once and for all. He took swan flasks that had twisted necks for the experiment and boiled meat broth in it. The design of the flask was such that it allowed exchange or air from outside to inside but prevented the entry of microorganisms. If any microbes were to enter the flask they would get caught in the twisted neck of the flask. The broth remained clear for a long amount of time as long as the flask was kept intact. Once the flask was turned, which led to entry of microbes into the broth, it became cloudy.

John Tyndall, an Irish physicist, advanced the work of Louis Pasteur and finally the theory of spontaneous generation was disproved. Not much is known about Tyndall’s experiment on spontaneous generation.

In 1862, the French Academy of Sciences, announced a prize for the scientists who shed new light on the spontaneous generation controversy and appointed a jury to decide the winner. Louis pasteur was awarded the Alhumbert Prize from the Paris Academy of Sciences for his work that totally threw away the concept of spontaneous generation. 1n 1864, Pasteur was quoted saying in a lecture: “Omne vivum ex vivo” (“Life only comes from life”). Pasteur and other scientists started to use the word biogenesis for the origin of life which again meant that life comes only from another life.

This sums up the theory of spontaneous generation. Keep visiting BYJU’S Biology for more interesting topics.

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Unraveling The Mystery: Identifying The Problem In Redi’s Experiment

The history of science is filled with remarkable experiments that have shaped our understanding of the world around us. One such experiment that holds great significance is Redi’s experiment. By unraveling the mystery behind Redi’s experiment, we can gain valuable insights into the importance of identifying and addressing experimental errors in scientific research.

Table of Contents

Hook: Briefly mention the significance of Redi’s experiment in the history of science

Redi’s experiment marked a turning point in the field of biology, challenging long-held beliefs and paving the way for a more accurate understanding of the natural world. It played a crucial role in debunking the concept of spontaneous generation, which was widely accepted during Redi’s time.

To truly comprehend the significance of Redi’s experiment, we must delve into the details of the experiment itself and identify the flaw that led to an incorrect conclusion. By doing so, we can appreciate the importance of critical thinking and questioning in scientific research.

Redi’s experiment, conducted in the 17th century, aimed to challenge the prevailing belief in spontaneous generation. This belief suggested that living organisms could arise spontaneously from non-living matter. Redi sought to test this theory by focusing on the generation of maggots from decaying meat.

Describe the setup and procedure of the experiment

Redi set up multiple jars, each containing a piece of meat. Some jars were left open to the air, while others were covered with gauze to prevent flies from accessing the meat. The purpose of this setup was to determine whether maggots would appear on the meat, and if so, whether they were the result of spontaneous generation or the presence of flies.

Upon conducting the experiment, Redi observed that maggots only appeared on the meat in the open jars, where flies had access. In contrast, the covered jars remained free of maggots. Based on these observations, Redi concluded that maggots did not arise spontaneously from the meat, but rather from the eggs laid by flies.

However, Redi’s experiment was not without its flaws. The flaw lay in the fact that the gauze used to cover the jars prevented flies from accessing the meat, but it also prevented other potential sources of contamination from reaching the meat. This oversight led Redi to an incorrect conclusion, as he failed to consider the possibility of microorganisms or other small organisms present in the air or on the meat itself.

Discuss the importance of identifying and addressing experimental errors in scientific research

Redi’s experiment serves as a powerful reminder of the significance of identifying and addressing experimental errors in scientific research. It highlights the need for meticulous attention to detail and the consideration of all possible variables that may impact the outcome of an experiment.

In the subsequent sections of this blog post, we will explore how Redi’s experiment challenged the concept of spontaneous generation and the role it played in shaping the scientific method. We will also examine the experiments conducted by subsequent scientists to further disprove spontaneous generation, ultimately correcting the misconception and solidifying the understanding of biogenesis.

Overview of Redi’s Experiment

Redi’s experiment is a significant milestone in the history of science as it played a crucial role in challenging the prevailing belief in spontaneous generation . By conducting a well-designed experiment, Redi was able to provide evidence that contradicted the notion of life spontaneously arising from non-living matter.

Purpose of Redi’s Experiment

The primary objective of Redi’s experiment was to investigate the source of maggots found on decaying meat. During his time, it was commonly believed that maggots spontaneously generated from rotting organic material. Redi sought to test this hypothesis and provide a more accurate explanation for the presence of maggots.

Setup and Procedure of the Experiment

To conduct his experiment, Redi set up three different jars. In the first jar, he placed a piece of meat uncovered, allowing flies to access it. In the second jar, he covered the meat with a fine gauze, preventing flies from reaching it. The third jar remained empty and served as a control.

Over a period of time, Redi observed that maggots only appeared on the meat in the uncovered jar, while the covered jar and the control jar remained free of maggots. This observation led him to question the prevailing belief in spontaneous generation.

Based on his observations, Redi concluded that the maggots found on the uncovered meat originated from fly eggs. He proposed that flies laid their eggs on the meat, and the eggs hatched into maggots. This conclusion challenged the widely accepted belief that maggots spontaneously generated from decaying matter.

Redi’s experiment provided a crucial piece of evidence against spontaneous generation and laid the foundation for further scientific inquiry into the origin of life.

The significance of Redi’s experiment lies not only in its findings but also in the methodology employed. Redi’s experiment was carefully designed to control variables and eliminate potential sources of error. This approach set a precedent for future scientific investigations and emphasized the importance of rigorous experimentation.

Redi’s experiment, however, was not without its flaws, which became apparent in subsequent studies. While his experiment successfully disproved spontaneous generation in the case of maggots, it did not address the broader concept of spontaneous generation in other organisms.

Nonetheless, Redi’s experiment served as a catalyst for further scientific exploration and paved the way for subsequent scientists to build upon his findings. It sparked a series of experiments conducted by scientists such as Louis Pasteur, who further discredited the idea of spontaneous generation.

In conclusion, Redi’s experiment was a pivotal moment in the history of science. It challenged the prevailing belief in spontaneous generation and highlighted the importance of careful experimentation and critical thinking. By identifying the problem in Redi’s experiment, we can appreciate the significance of addressing experimental errors and the enduring relevance of Redi’s work in shaping modern scientific practices.

Identifying the Problem

In this section, we will delve into the flaws in Redi’s experiment and how these flaws led to an incorrect conclusion. It is crucial to identify and address experimental errors in scientific research to ensure accurate results and reliable conclusions.

Highlight the flaw in Redi’s experiment

Redi’s experiment aimed to challenge the prevailing belief in spontaneous generation, which suggested that living organisms could arise spontaneously from non-living matter. However, there was a fundamental flaw in Redi’s experiment that compromised its validity.

The flaw in Redi’s experiment was the use of sealed containers. Redi placed pieces of meat in jars, covering some with gauze and leaving others open. He observed that maggots only appeared in the open jars, while the covered jars remained free of maggots. Based on this observation, Redi concluded that maggots were not spontaneously generated but were instead the offspring of flies.

The flaw in Redi’s experiment lies in the fact that the sealed containers prevented flies from accessing the meat. As a result, the flies could not lay their eggs on the meat, which would have led to the development of maggots. By eliminating the flies from the equation, Redi inadvertently eliminated the source of the maggots, leading to the false conclusion that spontaneous generation did not occur.

Redi’s experiment serves as a reminder of the importance of identifying and addressing experimental errors in scientific research. Scientific progress relies on the ability to critically analyze experimental procedures and results . By recognizing and rectifying flaws in experiments, scientists can ensure the accuracy and reliability of their findings.

Identifying and addressing experimental errors also helps to prevent the perpetuation of misconceptions and false conclusions. In the case of Redi’s experiment, the flawed methodology led to an incorrect rejection of spontaneous generation. It was only through subsequent experiments and the correction of these errors that the true understanding of biogenesis, the theory that living organisms arise from other living organisms, was established.

By learning from Redi’s experiment, scientists today are better equipped to design experiments that minimize errors and produce reliable results. The scientific method, which emphasizes rigorous experimentation and critical thinking, has evolved to incorporate safeguards against experimental flaws . This ensures that scientific knowledge continues to advance and contribute to our understanding of the natural world.

In the next section, we will explore the historical significance of spontaneous generation and how Redi’s experiment challenged this prevailing belief. Stay tuned for an intriguing journey through scientific history!

The Role of Spontaneous Generation

Spontaneous generation, also known as abiogenesis, is the belief that living organisms can arise spontaneously from non-living matter. This concept was widely accepted during the time of Francesco Redi, the Italian physician and biologist who conducted the famous experiment that challenged this prevailing belief. Understanding the role of spontaneous generation in Redi’s experiment is crucial to unraveling the mystery behind his groundbreaking findings.

Define spontaneous generation and its historical significance

Spontaneous generation was a widely held belief for centuries, dating back to ancient times. It suggested that living organisms, such as maggots, mice, and even microorganisms, could arise spontaneously from decaying organic matter or other non-living substances. This concept played a significant role in shaping the understanding of life’s origins and the development of scientific thought.

Discuss the prevailing belief in spontaneous generation during Redi’s time

During the 17th century, when Redi conducted his experiment, the belief in spontaneous generation was deeply ingrained in the scientific community. It was commonly believed that maggots, for example, spontaneously generated from rotting meat. This belief was supported by observations that seemed to indicate the sudden appearance of these organisms in the absence of any visible source.

Explain how Redi’s experiment challenged the concept of spontaneous generation

Redi’s experiment aimed to challenge the notion of spontaneous generation by investigating the origin of maggots in decaying meat. He set up several jars, each containing a piece of meat. Some jars were left open, while others were covered with gauze to prevent flies from accessing the meat. Redi observed that maggots only appeared in the open jars, where flies could land and lay their eggs on the meat. The covered jars remained free of maggots.

This experiment provided compelling evidence against spontaneous generation. It demonstrated that the presence of flies, rather than the decaying meat itself, was necessary for the appearance of maggots. Redi’s findings suggested that living organisms, such as maggots, do not arise spontaneously from non-living matter but instead come from pre-existing living organisms.

Redi’s experiment challenged the prevailing belief in spontaneous generation and paved the way for further scientific inquiry into the origins of life.

Redi’s experiment played a pivotal role in debunking the concept of spontaneous generation. By demonstrating that maggots did not arise spontaneously from decaying meat, but rather from the eggs laid by flies, Redi provided compelling evidence against this long-held belief. His findings sparked a revolution in scientific thought and laid the foundation for the understanding of biogenesis, the principle that living organisms arise from pre-existing living organisms.

Understanding the role of spontaneous generation in Redi’s experiment is crucial to appreciating the significance of his findings. It highlights the importance of questioning prevailing beliefs and conducting rigorous experiments to uncover the truth. Redi’s experiment not only challenged the concept of spontaneous generation but also contributed to the development of the scientific method.

In modern scientific practices, Redi’s experiment serves as a reminder of the enduring relevance of critical thinking and empirical evidence. It encourages scientists to question established theories and investigate alternative explanations. By learning from Redi’s experiment, we can continue to advance our understanding of the natural world and make groundbreaking discoveries.

Correcting the Misconception

Introduce the work of subsequent scientists who built upon redi’s experiment.

After Francesco Redi’s groundbreaking experiment, subsequent scientists continued to build upon his work to further disprove the concept of spontaneous generation. One such scientist was Lazzaro Spallanzani, an Italian biologist who conducted experiments in the late 18th century.

Spallanzani’s experiments involved boiling broth and sealing it in flasks. By creating a sterile environment, he aimed to prevent any potential contamination that could lead to the formation of life. Spallanzani observed that no life forms appeared in the sealed flasks, even after prolonged periods of time. This experiment provided further evidence against the idea of spontaneous generation.

Discuss the experiments conducted by these scientists to further disprove spontaneous generation

Louis Pasteur, a French chemist and microbiologist, also contributed significantly to the understanding of biogenesis. In the mid-19th century, Pasteur conducted experiments that definitively disproved the concept of spontaneous generation.

Pasteur’s experiments involved using swan-necked flasks filled with nutrient broth. The long, curved neck of the flask allowed air to enter but prevented any potential contaminants from reaching the broth. Pasteur observed that no microbial growth occurred in the broth, even when left undisturbed for extended periods.

To further solidify his findings, Pasteur tilted the flasks, allowing the broth to come into contact with the curved neck. This resulted in microbial growth, demonstrating that contamination from the outside environment was necessary for life to form. Pasteur’s experiments conclusively proved that life only arises from pre-existing life, refuting the idea of spontaneous generation.

Explain how these experiments corrected the misconception and solidified the understanding of biogenesis

The experiments conducted by Spallanzani and Pasteur played a crucial role in correcting the misconception of spontaneous generation. They provided concrete evidence that life does not arise spontaneously but rather from pre-existing life.

By meticulously controlling the experimental conditions and eliminating potential sources of contamination, these scientists demonstrated that the formation of life requires the presence of living organisms or their reproductive elements. Their experiments helped establish the principle of biogenesis, which states that living organisms can only arise from other living organisms.

These findings revolutionized the field of biology and had a profound impact on scientific understanding. The experiments conducted by Spallanzani and Pasteur laid the foundation for the modern understanding of the origin of life and the processes involved in reproduction.

Lessons Learned

Reflect on the importance of critical thinking and questioning in scientific research.

The work of scientists like Redi, Spallanzani, and Pasteur highlights the importance of critical thinking and questioning in scientific research. They recognized the prevailing beliefs of their time and set out to challenge them through rigorous experimentation.

Their ability to identify flaws in existing theories and design experiments to test them allowed for the correction of misconceptions and the advancement of scientific knowledge. This serves as a valuable lesson for scientists today, emphasizing the need to question established ideas and continually seek evidence to support or refute them.

Discuss the impact of Redi’s experiment in shaping the scientific method

Redi’s experiment not only corrected a misconception but also played a significant role in shaping the scientific method. His experiment followed the principles of observation, hypothesis formulation, experimentation, and conclusion drawing. This systematic approach provided a framework for future scientists to follow in their own research.

The scientific method, as exemplified by Redi’s experiment, emphasizes the importance of reproducibility, controlled experimentation, and critical analysis. It has become the cornerstone of scientific inquiry, enabling researchers to investigate phenomena, test hypotheses, and arrive at reliable conclusions.

Highlight the enduring relevance of Redi’s experiment in modern scientific practices

Although Redi’s experiment was conducted centuries ago, its relevance in modern scientific practices remains significant. The experiment serves as a reminder of the importance of careful experimental design, control of variables, and the need to address potential sources of error.

Redi’s experiment also underscores the significance of peer review and replication in scientific research. By subjecting their work to scrutiny and encouraging others to replicate their experiments, scientists can ensure the validity and reliability of their findings.

In conclusion, the work of subsequent scientists who built upon Redi’s experiment, such as Spallanzani and Pasteur, played a crucial role in correcting the misconception of spontaneous generation. Their experiments provided concrete evidence against the idea and solidified the understanding of biogenesis. These findings highlight the importance of critical thinking, questioning established beliefs, and following the scientific method. Redi’s experiment continues to have enduring relevance in modern scientific practices, emphasizing the need for careful experimental design and the importance of peer review and replication.

In this section, we will delve into the lessons that can be learned from Francesco Redi’s experiment and its impact on the scientific community. Redi’s experiment not only challenged the prevailing belief in spontaneous generation but also highlighted the importance of critical thinking and questioning in scientific research. Let’s explore the lessons we can draw from this groundbreaking experiment.

Redi’s experiment serves as a powerful reminder of the significance of critical thinking in scientific research. By questioning the prevailing belief in spontaneous generation, Redi was able to design an experiment that challenged the existing paradigm. This highlights the importance of skepticism and the need to question established theories and beliefs in order to advance scientific knowledge.

Critical thinking involves analyzing information, evaluating evidence, and considering alternative explanations. It encourages scientists to approach their research with an open mind and to constantly question their findings. Redi’s experiment demonstrates that by critically examining the existing beliefs, scientists can uncover new insights and challenge long-held assumptions.

Redi’s experiment played a significant role in shaping the scientific method. The scientific method is a systematic approach used by scientists to investigate natural phenomena and acquire knowledge. It involves making observations, formulating hypotheses, conducting experiments, analyzing data, and drawing conclusions.

Redi’s experiment exemplifies the steps of the scientific method. He observed that maggots appeared on decaying meat, formulated a hypothesis that challenged the prevailing belief in spontaneous generation, designed an experiment to test his hypothesis, and drew conclusions based on the results of his experiment. This experiment laid the foundation for future scientists to follow a similar methodology in their research.

Although Redi’s experiment was conducted centuries ago, its relevance in modern scientific practices cannot be overstated. The principles of critical thinking, questioning, and experimentation that Redi employed are still fundamental to scientific research today.

Scientists continue to question existing theories, design experiments to test hypotheses, and critically analyze data to draw conclusions. Redi’s experiment serves as a reminder that scientific knowledge is not static but constantly evolving. It encourages scientists to challenge established beliefs and push the boundaries of understanding.

In addition, Redi’s experiment also emphasizes the importance of rigor and accuracy in scientific research. Identifying and addressing experimental errors is crucial to ensure the validity and reliability of scientific findings. By recognizing the flaw in Redi’s experiment, we learn the significance of meticulous experimental design and the need to consider all possible variables.

In conclusion, Redi’s experiment provides valuable lessons for the scientific community. It underscores the importance of critical thinking, questioning, and experimentation in scientific research. Furthermore, it highlights the impact of Redi’s experiment in shaping the scientific method and its enduring relevance in modern scientific practices. As we continue to explore the mysteries of the natural world, let us be inspired by Redi’s curiosity and commitment to uncovering the truth through scientific inquiry.

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Francesco Redi: History and Significance

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Francesco Redi was an Italian scientist most famous for his experimental work that refuted the spontaneous generation theory. His experiment with meat in glass containers was one of the earliest controlled experiments.

Who is Francesco Redi?

Francesco Redi was a scientist born in Arezzo, Italy on February 18, 1626. He completed degrees in medicine and philosophy at the University of Pisa. After graduating, Redi moved to Florence to become the physician to the Grand Duke of Tuscany.

Redi was inspired by the work of William Harvey, who correctly described blood circulation around the body. It led him to develop his own experimental work. His most famous work was a paper entitled, Esperienze Intorno alla Generazione degl'Insetti (Experiments on the Generation of Insects) which he published in 1668. This work provided evidence against the spontaneous generation theory.

The spontaneous generation theory, which claims living things can form from non-living objects, had been put forward by Aristotle and had been widely accepted for centuries. People believed that maggots would just emerge from rotting meat. In the experiment Redi prepared three groups of jars, each with a pieces of meat inside them. One group of jars was covered with gauze, one group was left open, and one group was completely sealed.

In the group of jars that were left open, Redi found maggots on the meat. Redi noticed that in the jars that were completely sealed, there were no maggots. In the group of jars that were covered in gauze, he noticed that there were no maggots on the meat, but maggots did appear on top of the gauze. This experiment provided evidence which refuted the spontaneous generation theory. He showed that maggots came from eggs laid by flies. This experiment was important as it was one of the first controlled experiments in history. Modern day scientific experiments require controls to eliminate the impact of other variables on the results of the experiment.

Redi died on March 1, 1697 in Pisa.

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Francesco redi’s accomplishments.

• Use of controlled experiments
• Disproving the spontaneous generation theory
• Discovery that snake venom is not produced in the gallbladder

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SPONTANEOUS GENERATION (ABIOGENESIS)

Spontaneous generation (abiogenesis) is the mistaken hypothesis that living organisms are capable of being generated from non-living things. Mankind for many centuries (even till the time of Aristotle in 4 th century BC) previously believed that non-living things such as meat and even decaying organic matter can generate living things (e.g. maggot). The belief that life can emanate from non-life was widely accepted as at the time even by scientists who could have experimented on it to either disprove or accept the theory.

Nevertheless several scientists (including John Needham , Francesco Redi , John Tyndall and Louis Pasteur ) as at the time abiogenesis was accepted were curious on how the concept of abiogenesis was true and relevant. This led this notable scientist’s to conduct series of experiments which led to the final disapproval of the theory of spontaneous generation.

Spontaneous generation (though an obsolete biological theory) sparked a lot of controversies for many years in the world; and scientists, religious leaders and especially philosophers had different views as to how life originated. A wider part of the society as at the time believed that life could originate from nothing especially from non-living things or some kind of vital forces that were present in decomposing organic matter.

• FERDINAND J. COHN (1828-1898)

PAUL EHRLICH (1854-1915)

• HANS CHRISTIAN JOACHIM GRAM (1853-1938)
• DMITRI IWANOVSKI (1864-1920)
• ANTHONY VAN LEEUWENHOEK (1632-1723)
• JOSEPH LISTER (1827-1912)
• Historical Perspectives of Microbiology

The concept of spontaneous generation was very appealing to some scientists and even philosophers as at the time who believed strongly that life originated from non-life, but religious leaders fought against it because they believed that life originated from a supernatural being. In the subsequent pages, we shall discover that spontaneous generation does not occur, and that life does not emanate from non-life but from pre-existing life as exemplified by the notable works of Louis Pasteur amongst others.

How did life originated? The increase in knowledge, human’s quest for understanding life and the development of the scientific method gave man a better perspective of his environment and how the organisms in it (inclusive of microorganisms) directly or indirectly affect him. Previously, people believed so many things even when they did not conduct experiment to know if what they observed in their immediate natural environment is true or not. The theory of spontaneous generation held-sway for a long period of time before it was challenged and disproven through the experimental works of some notable scientists like Louis Pasteur. It is noteworthy that the scientists who attempted to disprove abiogenesis carried out their experiments or testing based on the scientific method.

Scientific method is the general approach that involves series of systematic steps or modus operandi used by scientists (including microbiologists) to conduct research. This methodical approach enables scientists (anywhere in the world) to conduct make scientific inquiries and arrive at conclusive answers to their observations or questions; and scientific method is a universally accepted approach of conducting research by scientists. The basic steps involved in the scientific method (which may vary depending on the experimentation) are elaborated in Figure 1.

Before it was disproved, people believed that life originated from non-living matter, a biological phenomenon known as spontaneous generation. Biogenesis is an alternative hypothesis to spontaneous generation; and it postulates that living organisms originated from pre-existing living things. Those who supported the claims of spontaneous generation (i.e. abiogenesis) believed that living organisms arise from non-living things or decomposing organic matter; and this hypothesis was invoke even till the late 19 th century before it was disproven by series of experiments conducted by notable scientists.

Francesco Redi (1626-1697) , an Italian Physicianwas the first to attack the theory of spontaneous generation, and this happened in 1668. At a time when it was widely believed that maggots arose from decaying meat, Redi carried out his experiment by filling a series of jars with decaying meat in order to disprove this belief. Some of the jars was left completely open to the air ( the test ); others were completely sealed while the remaining jars was covered with fine clothe or gauze (which prevented insects from entering). The flasks or jars that were completely sealed and covered with gauze served as the controls.

Francesco Redi believed that flies deposited eggs on the decaying meat, and this resulted to the development of maggots on the meat. After some days, it was discovered that maggots appeared only in the open jars in which the flies could easily reach and lay their eggs. Maggots did not appear in the jars that where completely sealed or covered with gauze. The laying of eggs on the decaying meat led to the development of maggots on the meat, and this was enough for Redi to disprove the theory of spontaneous generation. Francesco Redi challenged the theory of spontaneous generation by showing in his jar-decaying meat experiment that the maggot that appeared on the decaying meat (in the opened jar) came from the eggs of the fly deposited on the meat, and that the meat did not produce them. Despite Redi’s significant experiment (which gave impetus to the origin of life), the theory of spontaneous generation or abiogenesis remained strong and this continued for many centuries.

John Needham (1713-1781) used the boiling technique to determine whether or not boiling killed microorganisms. Needham supported the theory of spontaneous generation with his mutton or chicken broth boiling flask technique. He boiled mutton broth and put it in a flask which was tightly sealed after the broth was introduced in it. It was believed that boiling kills microorganisms. Needham allowed the flask for a long period of time, and discovered later that microorganisms developed in the broth even after boiling. Though his experiment supported abiogenesis; the fight to disprove spontaneous generation continued.

Lazzaro Spallanzani (1729-1799) , an Italian cleric boiled nutrient solutions in flask, and he showed in his experiment (which was a modification of Needham’s) that flask containing broth when sealed and boiled had no microbial growth. He drew out air from the flask before boiling in order to create a partial vacuum in the medium. Lazzaro was not convinced with Needham’s experiment because he contemplated that microorganisms could have entered the broth after it was boiled and before it was sealed. He showed in his significant work that air carried germs or microorganisms to the broth, and that air could support the growth of the organisms in the broth. However, Lazzaro’s experiment was still not accepted by supporters of spontaneous generation who believed that abiogenesis could not occur in the absence of air.

The theory of spontaneous generation was later put to rest and totally disproven by the significant experiments of Louis Pasteur (1822-1895) in 1859 and John Tyndall ( 1820-1893 ), an English physicist who extended Pasteur’s work by working on heat-resistant bacteria . A French chemist and microbiologist, Pasteur used the swan-necked flask experiment ( Figure 2 ) to disprove the theory of spontaneous generation. Louis Pasteur improved on the works of Needham and Spallanzani by boiling meat broth in bent-flasks which was opened to the air. Pasteur suggested that microorganisms in the air (which could contaminate the sterile broth) would be trapped on the sides of the bent flasks before they could finally reach the broth; and that if sterile broth had no prior contact with microorganisms, the broth would still remain sterile or free from microbes.

Louis Pasteur boiled meat broth in a flask and heated the neck of the flask in a flame until it became bent or curved (i.e. swan-necked). Though air could easily enter the flask, microorganisms in the air would be trapped in the neck of the bent flask. This was Pasteur’s idea of disproving the theory of spontaneous generation. The curved or bent flasks containing the broth were boiled to kill any form of microorganisms in it; and the flask was observed for a period of time for any possible microbial growth. But if the neck of the bent-flask was broken, dust particles or air-borne microbes would enter the flask and the broth will become polluted, and this will support the growth of germs.

Pasteur’s swan-necked experiment showed that the broth remained sterile for months because air-borne microbes were trapped in the bent-neck of the flask. Louis Pasteur then concluded that life only arises from life, and this is known as biogenesis. Though Louis Pasteur’s work laid the theory of spontaneous generation to rest; his notable experiment also showed that microbes are ubiquitous i.e. they are everywhere (even in the air).    

The theory of spontaneous generation was wildly acceptable to many as at the time it was invoke, but the experiments of Louis Pasteur and that of John Tyndall helped in laying it to rest once and for all. John Tyndall ( 1820-1893 ) gave impetus to the experiment of Louis Pasteur by showing in 1877 that dust particles indeed harboured microbes, and that the absence of it could cause the broth to remain sterile.

Tyndall went a step further to show the existence of heat-resistant forms of bacteria known as endospores , which are not easily killed by boiling. It is possible that the bacterial growth that was observed in Needham’s experiment after boiling was endopores (i.e. heat-resistant forms of bacteria). The observance of bacterial growth after boiling chicken broth made Needham to propose in 1745 that spontaneous generation did occur because microbes grew after the process. However, Pasteur and Tyndall’s experiment put a final stop to the theory of spontaneous generation and they convincingly showed that abiogenesis did not actually occur.   

Barrett   J.T (1998).  Microbiology and Immunology Concepts.  Philadelphia,   PA:  Lippincott-Raven Publishers. USA.

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Brooks G.F., Butel J.S and Morse S.A (2004). Medical Microbiology, 23 rd edition. McGraw Hill Publishers. USA. Pp. 248-260.

Chung K.T, Stevens Jr., S.E and Ferris D.H (1995). A chronology of events and pioneers of microbiology. SIM News , 45(1):3–13.

Nester E.W, Anderson D.G, Roberts C.E and Nester M.T (2009). Microbiology: A Human Perspective. Sixth edition. McGraw-Hill Companies, Inc, New York, USA.

Salyers A.A and Whitt D.D (2001). Microbiology: diversity, disease, and the environment. Fitzgerald Science Press Inc. Maryland, USA.

Slonczewski J.L, Foster J.W and Gillen K.M (2011). Microbiology: An Evolving Science. Second edition. W.W. Norton and Company, Inc, New York, USA.

Summers W.C (2000). History of microbiology. In Encyclopedia of microbiology, vol. 2, J. Lederberg, editor, 677–97. San Diego: Academic Press.

Talaro, Kathleen P (2005). Foundations in Microbiology. 5 th edition. McGraw-Hill Companies Inc., New York, USA.

Wainwright M (2003). An Alternative View of the Early History of Microbiology. Advances in applied microbiology. Advances in Applied Microbiology, 52:333–355.

Willey J.M, Sherwood L.M and Woolverton C.J (2008). Harley and Klein’s Microbiology. 7 th ed. McGraw-Hill Higher Education, USA.

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Chika Ejikeugwu (PhD, 2017, UNIZIK, Nigeria) is a Fellow of the Alexander von Humboldt (AvH) Stiftung in Germany. Dr. Chika Ejikeugwu is currently a Research Fellow at the Helmholtz-Zentrum für Umweltforschung GmbH-UFZ, Leipzig, Germany, where he is working on "the soilRESIST project to investigate the effects of antibiotic mixtures on soil microbiomes." He founded Africa's Number 1 Microbiology website, www.MicrobiologyClass.net. Dr. Chika Ejikeugwu was a DAAD postdoctoral fellow at Bundesanstalt für Materialforschung und -prüfung (BAM), Berlin, Germany (2021) and a MIF Postdoctoral Fellow at Kyoto University, Kyoto, Japan (2018). In 2021, he was awarded the Young Investigator Award on Antimicrobial Resistance (AMR) by Institute Mérieux in France. Dr. Chika Ejikeugwu is a member of the Global Young Academy in Germany, and a member of other professional (microbiology) societies including Applied Microbiology International (AMI), European Society of Clinical Microbiology and Infectious Diseases (ESCMID), Nigerian Society for Microbiology (NSM) and American Society for Microbiology (ASM). He holds a doctorate degree in Pharmaceutical Microbiology and Biotechnology. Dr. Chika Ejikeugwu is a Senior Lecturer & Researcher at Enugu State University of Science & Technology (ESUT), Nigeria where he mentors undergraduate and postgraduate students on microbiology & other aspects of life. He has a flair for teaching, research and community service.

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Francesco Redi’s experiment

• March 4, 2023 March 4, 2023
• History of Microbiology , Microbiology

Francesco Redi was an Italian scientist who conducted a famous experiment in the 1660s. Francesco Redi’s experiment was important in helping to disprove the theory of spontaneous generation, which the belief that life could arise from non-living matter. that helped to disprove the theory of spontaneous generation and provide evidence for the theory of biogenesis.

Redi’s experiment was significant because it challenged the prevailing belief in spontaneous generation and provided evidence in support of the theory of biogenesis, which suggests that living organisms only arise from other living organisms. This experiment helped to pave the way for future experiments in microbiology and ultimately led to the development of the germ theory of disease.

The aim of Redi’s experiment was to test the hypothesis that “ maggots could spontaneously arise from decaying meat. “

• Three wide-mouthed glass jars with lids : Redi used three glass jars to hold the meat, one of which was left open to the air, one covered with gauze, and one sealed completely.
• Raw meat : Redi used a piece of raw meat, such as a chunk of beef, to test the theory of spontaneous generation.
• Fine gauze or mesh : Redi covered one of the jars with a fine mesh to allow air to enter but prevent flies from laying their eggs on the meat.

Redi designed an experiment in which he used three jars. In the first jar, he placed a piece of meat without any covering. Then in the second jar, he placed a piece of meat covered with gauze, which would allow air to pass through but prevent flies from reaching the meat. In the third jar, he sealed the meat with a lid, preventing both air and flies from reaching the meat.

Redi observed the jars for several days, documenting any changes or developments that occurred in each jar. He recorded the presence of flies, maggots, and any other organisms that appeared in the jars.

• The jar with uncovered meat developed maggots.
• The jar with gauze-covered meat did not produce any maggots, Instead, fly eggs were found on the gauze.
• The sealed jar, which prevented flies from accessing the meat, did not produce any maggots or other organisms.

Significance of Francesco Redi’s experiment

• Francesco Redi’s experiment disproved spontaneous generation.
• It laid the foundation for the germ theory of disease, encouraging scientific inquiry and the development of the scientific method.
• It was a significant milestone in the history of science, leading to further advancements in biology and medicine.

Francesco redi experiment conclusion

• Redi’s experiment showed maggots on decaying meat came from flies, not from the meat itself.
• The experiment supported the theory of biogenesis: life comes from other life.
• The experiment disproved spontaneous generation: life doesn’t come from non-living matter.

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April 8, 2024 feature

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The spontaneous emergence of 1D superconducting stripes at a 2D interface in an oxide heterostructure

by Ingrid Fadelli , Phys.org

Unconventional superconducting states are states of superconductivity rooted in physical processes that do not conform with the conventional theory of superconductivity, namely Bardeen, Cooper and Schrieffer (BCS) theory. These states are characterized by close interactions between magnetism and superconductivity.

Researchers at University of Science and Technology of China (USTC), Tsinghua University and Fudan University have recently been trying to better understand the mechanisms underlying unconventional superconductivity. Their paper , published in Nature Physics , unveiled the spontaneous emergence of a spatially varying superconducting state in an oxide heterostructure, specifically at the interface between KTaO 3 and ferromagnetic EuO.

"Our recent paper studied the unconventional superconductivity at the interface between (110)-oriented KTaO 3 (KTO) and ferromagnetic EuO," Ziji Xiang from USTC, co-author of the paper, told Phys.org. "Both KTO and EuO are insulators, yet their interface in such a heterostucture hosts two-dimensional electron gas (2DEG) that becomes superconducting at low temperatures."

The recent study by this team of researchers had two key objectives. The first was to unveil new superconducting states in in an oxide heterostructure with a ferromagnetic overlayer (i.e., EuO), The second was to explore the evolution of interface superconductivity following targeted experimental manipulations, such as changing the carrier density (n s ) of the interface.

"Our research is inspired by the idea that unconventional superconductivity usually emerges in proximity to magnetism," Xiang said. "In particular, for copper-based and iron-based high-temperature superconductors , many of the proposed superconducting pairing mechanisms are closely connected to magnetism; moreover, the interplay between magnetism and superconductivity may give birth to more peculiar phases of matter, including the pair-density-wave (PDW) order with a spatially oscillating superconducting order parameter and finite-momentum pairing which has been an intense focus of research recently."

The EuO/KTO heterostructure examined by Xiang and his colleagues exhibits a strong ferromagnetic proximity effect elicited by the EuO overlayer. This effect makes it an ideal platform to study unconventional superconductivity.

"The first report on the superconductivity at the EuO/KTO interface was published in 2021, focusing on the KTO (111) interface," Xiang said. "We have since worked on the EuO/KTO (110) interface (considering its improved interface quality), at which we revealed the emergence of two-dimensional superconductivity in a previous paper ."

The researchers prepared the EuO/KTO(110) heterostructures used in their experiments using a technique known as molecular-beam epitaxy. They specifically grew EuO films on top of (110)-oriented KTO single crystalline substrates.

"By controlling the growth conditions, we were able to obtain heterostructures with different interfacial carrier density n s ," Xiang said. "We then fabricated standard Hall-bar devices for conducting electrical transport measurements. The Hall-bar devices were specially designed such that the resistance of the interfacial 2DEG can be simultaneously measured for two orthogonal directions of applied electric current: on the KTO (110) surface, these two orthogonal directions are [001] and [1-10]."

In addition to conducting transport experiments, the researchers analyzed the heterostructures using a magnetometry technique based on a scanning superconducting interference device (scanning SQUID), in collaboration with the lab led by Prof. Yihua Wang at Fudan University. This technique allowed them to characterize the magnetic properties of their samples.

In collaboration with Prof. Zheng Liu's research group at Tsinghua University, the researchers also performed a series of first-principles calculations, to better understand their experimental observations. These calculations were aimed at outlining the electronic band structure of the interfacial 2DEG.

"Firstly, our electrical transport revealed a highly unusual in-plane anisotropy of the superconducting 2DEG at the EuO/KTO(110) interface," Xiang said. "That is to say, both the transition temperature (T c ) and the upper critical field (H c2 , the magnetic field at which the superconductivity breaks down) appear to be strongly dependent on the direction of applied electric current I; with I parallel to [001], both T c and H c2 are higher than the case of I parallel to [1-10]. Such directional dependence is very rare among superconductors."

Scanning SQUID imaging unveiled the occurrence of two successive diamagnetic transitions in the team's samples. This suggests that the directional dependence in transport they observed does indeed stem from the sub-micrometer co-existence of two superconducting phases.

"Based on our findings, we propose a scenario in which the superconducting phase with higher T c is a 'stripe' phase in which one-dimensional (1D) superconducting bundles aligned unidirectionally along [001] emerge," Xiang said.

"Coherent superconductivity is first developed within these 1D structures, giving rise to the directional-dependent T c and H c2 . The establishment of 2D superconductivity over the whole interface occurs only at a lower temperature."

The second central result is that the above-mentioned directional superconductivity only exists in heterostructures with low 2DEG carrier density (n s < ~8´10 13 cm -2 ). For 2DEGs with higher n s , the T c and H c2 never show any current-direction dependence. Hence, the emergence of proposed superconducting stripe phase must depend on band filling.

"Most importantly, both our experimental and theoretical investigations suggest that the 2DEG is strongly coupled to the EuO ferromagnetism only in the low-n s samples wherein the directional superconductivity is observed," Xiang said.

"Due to this strong coupling, the electronic bands of 2DEG show pronounced spin polarization. Thereby, we conclude that the formation of superconducting stripe phase must be closely related to such enhanced ferromagnetic proximity effect."

The recent work by Xiang and his colleagues unveils an unconventional superconducting state induced by the proximity with an oxide heterostructure. This state, marked by the spontaneous emergence of 1D superconducting stripes at a 2D interface, serves as an example of how dimensions can be reduced in superconducting states.

"This observed phenomenon reminds us of the dimension reduction reported in copper-oxide high-temperature superconductor La 2-x Ba x CuO 4 (x = 1/8), wherein 2D superconducting states develop in a three-dimensional system due to the interplay between superconductivity and charge/spin orders," Xiang said.

"These 2D superconducting states have been suggested to be PDW states. So, what is the nature of the emergent superconducting stripes in our heterostructures? Are they also manifestations of a PDW order or associated with some even more exotic superconducting phases?"

In their next studies, the researchers will try to answer these important questions. Their findings so far confirm that coupling with magnetism plays a crucial role in the realization of unconventional superconductivity.

In the future, Xiang and his colleagues plan to investigate the superconducting stripe phase they observed further, to find out more about its underlying superconducting pairing. This could allow them to better understand how this exotic superconducting state can emerge from electronic bands with a strong spin polarization.

"Unfortunately, the presence of EuO overlayer prevents the application of most spectroscopic probes for a direct study of the interface," Xiang added. "We have been working on the development of a technique that measures the superfluid density at the interface. By tracking the evolution of superfluid density with varying temperature, we can obtain valuable information about the primary thermodynamic properties of the superconducting stripe phase, which could be a crucial step towards a deeper understanding of the novel physics involved."

Journal information: Nature Physics

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5.1: Spontaneous Generation

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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

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.

Exercise \(\PageIndex{1}\)

What types of respiratory disease may be responsible?

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 (“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 17 th 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 17 th 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 \(\PageIndex{1}\)). Two were open to the air, two were covered with gauze, and two were tightly sealed. His hypothesis was supported when maggots developed in the uncovered jars, but no maggots appeared in either the gauze-covered or the tightly sealed jars. He concluded that maggots could only form when flies were allowed to lay eggs in the meat, and that the maggots were the offspring of flies, not the product of spontaneous generation.

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 \(\PageIndex{2}\)).

Exercise \(\PageIndex{2}\)

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

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

Exercise \(\PageIndex{3}\)

• 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?
• 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.”
• 1 K. Zwier. “Aristotle on Spontaneous Generation.” www.sju.edu/int/academics/cas...R.%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.