---
title: "Lazzaro Spallanzani | Microbiology"
description: "Lazzaro Spallanzani is the microbiologist who showed boiled broth stays sterile when sealed, helping disprove spontaneous generation and support biogenesis."
canonical: "https://fiveable.me/microbio/key-terms/lazzaro-spallanzani"
type: "key-term"
subject: "Microbiology"
unit: "Unit 3"
---

# Lazzaro Spallanzani | Microbiology

## Definition

Lazzaro Spallanzani was an 18th-century scientist whose broth experiments showed that microbes come from preexisting life, not spontaneous generation. In microbiology, he is a major early step toward biogenesis and germ theory.

## What It Is

Lazzaro Spallanzani is the scientist you usually meet when microbiology starts tracing how people proved that microbes do not just appear out of nowhere. His classic experiments with boiled broth showed that if nutrient broth was heated and sealed from air, it stayed clear, but if it was exposed to air, it spoiled. That result pushed students of microbiology away from spontaneous generation and toward the idea that contamination comes from living microbes already present in the environment.

What made his work so useful was the setup. Boiling the broth killed the microbes already in the liquid, so any later growth had to come from somewhere else. When the broth was kept airtight, nothing grew. When air could reach it, spoilage happened, which suggested that air was carrying microscopic life or particles that could seed growth. In other words, he was not just noticing decay, he was controlling one variable at a time.

That detail matters because spontaneous generation was a real scientific debate, not a cartoon mistake. People saw maggots on meat or microbes in rotting materials and assumed life was emerging from nonliving matter. Spallanzani’s approach challenged that by showing a cleaner cause-and-effect pattern: remove the source of contamination, and growth does not appear. The result fit better with biogenesis, the principle that life comes from preexisting life.

His work also sits right before later germ theory arguments. Spallanzani did not yet know about bacteria, sterilization technique, or modern aseptic methods, but he was already testing the idea that invisible organisms move through the environment and contaminate food or fluids. That is a microbiology mindset, even before the word microbiology was fully established.

One useful way to remember him is this: Spallanzani made a broth experiment into evidence about invisible life. He showed that if you heat a medium and keep it sealed, microbial growth is prevented. That simple result became part of the longer chain of evidence that led to modern lab sterilization, contamination control, and the rejection of spontaneous generation.

## Why It Matters

Spallanzani matters because his experiments explain one of the biggest turning points in microbiology, the move from guessing where living things come from to testing it with controlled methods. Once you understand his broth work, you can make sense of why microbiologists care so much about sterilization, contamination, and aseptic technique.

His results also connect directly to disease thinking. If microbes come from the environment and can enter nutrient-rich material, then the same logic can apply to wounds, food, water, and the body. That line of thinking supports germ theory of disease, where specific microorganisms are linked to specific illnesses instead of illness being blamed on vague causes.

Spallanzani is also a great example of how one experiment can challenge a popular theory without solving every detail at once. He did not have microscopes powerful enough to identify every organism in the broth, but he still used a careful comparison between sealed and exposed samples. That kind of comparison shows up all over microbiology, especially in lab reports and experimental design questions.

If you are reading about spontaneous generation, biogenesis, or the origins of germ theory, Spallanzani is one of the names that bridges the old idea and the modern one. He gives you the mechanism behind the historical shift: microbes were not magically appearing, they were entering from outside sources and reproducing in the right conditions.

## Connections

### Spontaneous Generation

Spallanzani’s work was aimed directly at this idea. Spontaneous generation claimed life could arise from nonliving matter, like broth or rotting meat. His sealed-broth experiments challenged that by showing that when contamination was blocked, no new growth appeared. He helped turn the debate into an experimental question instead of a philosophical one.

### Germ Theory of Disease

Spallanzani did not fully develop germ theory, but his findings supported the basic logic behind it. If microbes are carried in air and can contaminate broth, then microscopic organisms can also spread through bodies, wounds, and food. That makes his work an early step toward understanding disease as caused by microbes rather than by spontaneous decay.

### Biogenesis

Biogenesis is the idea that life comes from preexisting life, and Spallanzani’s experiments fit that principle. His broth did not generate life on its own after boiling and sealing, which suggested that any later growth had to come from living contaminants already present in the environment. This is the opposite of spontaneous generation.

### [Francesco Redi](/microbio/key-terms/francesco-redi)

Redi had already shown that maggots on meat came from flies, not from the meat itself. Spallanzani extended the same logic into microbiology by testing invisible life in broth instead of visible insects on food. Together, their work shows how scientific evidence accumulated over time against spontaneous generation.

## On the AP Exam

A quiz question or lab-analysis prompt may ask you to match Spallanzani with the sealed-broth experiment and explain what the results showed about contamination. The move you make is simple: identify the controlled condition, say what changed when air was allowed in, and connect that outcome to biogenesis rather than spontaneous generation. If you see a question about the origin of microbial growth in boiled nutrient broth, Spallanzani is the name tied to the evidence.

In a short-answer response, you might compare his setup to another anti-spontaneous-generation experiment and explain why sealing the flask mattered. In a lab discussion, you could use his work to describe why sterile media stay uncontaminated until exposed to microbes from the environment. The point is not to memorize his biography, but to recognize how his experiment supports the broader microbiology idea that growth comes from existing life.

## Lazzaro Spallanzani vs Francesco Redi

Both scientists challenged spontaneous generation, so they are easy to mix up. Redi worked with meat and maggots to show that flies produce maggots, while Spallanzani worked with boiled broth and sealing to show that microbial growth comes from outside contamination. If the example is insects on meat, think Redi. If the example is sterile broth and air exposure, think Spallanzani.

## Key Takeaways

- Lazzaro Spallanzani is best known in microbiology for experiments that showed boiled broth stays free of growth when it is sealed from outside contamination.
- His results challenged spontaneous generation and supported biogenesis, the idea that life comes from preexisting life.
- The air-exposure difference in his experiments mattered because it pointed to microbes in the environment as the source of spoilage.
- Spallanzani’s work is an early foundation for germ theory, since it helped scientists think about invisible organisms moving through air and causing contamination.
- If you remember one thing, remember the setup: boil, seal, and compare what happens when air is blocked versus when it is allowed in.

## FAQs

### What is Lazzaro Spallanzani in Microbiology?

Lazzaro Spallanzani was an 18th-century scientist who used boiled broth experiments to argue against spontaneous generation. In microbiology, he is remembered for showing that microbial growth comes from contamination by preexisting life, not from nonliving broth itself.

### What did Spallanzani’s broth experiment show?

He showed that boiled broth stayed clear when sealed in airtight containers, but spoiled when exposed to air. That difference suggested that microorganisms were coming from the air or environment, not appearing spontaneously inside the broth.

### How is Spallanzani different from Francesco Redi?

Redi tested spontaneous generation with meat and maggots, while Spallanzani tested it with boiled broth and microbes. They both challenged the same old idea, but Spallanzani’s work pushed the argument into the microscopic world.

### Why does Spallanzani matter for germ theory?

His experiments supported the idea that invisible microorganisms can move through the environment and contaminate materials. That idea fits the later germ theory view that specific microbes can cause disease and spoilage.

## Related Study Guides

- [3.1 Spontaneous Generation](/microbio/unit-3/1-spontaneous-generation/study-guide/pB2kvMEZf2G0qls2)

## About This Document

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- [llms-full.txt](https://fiveable.me/llms-full.txt): complete subject and unit listing
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