1. The Story of Spontaneous Generation

2. Spontaneous generation
Spontaneous generation is the idea that living things can be produced from non-living things.
From the time of the ancient Romans, through the Middle Ages, and until the late nineteenth century, it was generally accepted that some life forms arose spontaneously from non-living matter.

3. The Question
Where did life forms such as mice, maggots, and microorganisms come from?

4. Different Theories of Spontaneous Generation
Theory 1 = the spontaneous production of mice required placing sweaty underwear and husks of wheat in an open-mouthed jar, then waiting for about 21 days, during which time it was alleged that the sweat from the underwear would penetrate the husks of wheat, changing them into mice.

5. The Theories T2 = maggots arise spontaneously in rotting meat
T3 = microorganisms arise spontaneously in broth.

6. Different scientist tested theses theories over the years
Francesco Redi
An Italian doctor
Louis Pasteur
A French Scientist
Lazzaro Spallanzani
An Italian Scientist

7. Redi’s Experiment Question: where did maggots come from
Hypothesis: maggots came from the eggs of flies

8. Redi’s Experiment Procedure: Redi put rotting meat into three jars.
Jar 1 – open to the air
Jar 2 – covered with netting
Jar 3 – sealed off completely from outside

9. Redi’s Experiment Results: Jar 1 = maggots developed on rotting meat
Flies were observed on meat

10. Redi’s Experiment Results Jar 2 = maggots appeared on netting
Flies were observed on netting

11. Redi’s Experiment Results
Jar 3 = maggots did not appear at all in or around the sealed jar
No flies were observed near jar 3

12. Redi’s Experiment Conclusion:
The hypothesis was supported by the data and therefore accepted
Because there were no maggots in or around the jar it was concluded the maggots came from the fly eggs.

13. Spallanzani’s Experiment
Question: What causes microbes to form from decaying broth?
Hypothesis: Microbes come from the air. Boiling will kill microbes.

14. Spallanzani’s Experiment
Procedure:
Spallanzani put broth into four flasks
Flask 1 – left open to the air
Flask 2 – was sealed
Flask 3 – was boiled and left open
Flask 4 – was boiled then sealed

15. Spallanzani’s Experiment
Results
Flask 1 – left open to the air
Turned cloudy (microbes found)
Flask 2 – was sealed
Flask 3 – was boiled and left open
Flask 4 – was boiled then sealed
Did not turn cloudy (NO MICROBES)

16. Spallanzani’s Experiment
Conclusions:
The hypothesis was accepted
Because the combination of boiling the broth (killing bacteria that were in the jar to start) and sealing the jar (keeping bacteria in the air out) it was concluded that boiling does kill bacteria and that Microbes come from the air.

17. Pasteur’s Experiment
Question: Where do microbes come from to cause chicken broth to decay?
Hypothesis: Microbes come from cells of organisms on dust particles in the air; not from the air itself.

18. Pasteur’s Experiment Procedures: Control Group Experimental group
One flask of broth open to the air
Experimental group
One S-shaped flask that prevents dust from entering the flask.

19. Pasteur’s Experiment Procedure:
Pasteur put broth in both the open flask and into special S-Shaped flasks and boiled it.
S-shaped flask was used to trap any dust particles
Boiling was done to kill all the microbes already in the flask.

20. Pasteur’s Experiment Procedure (cont.)
Pasteur then watched to see if any changes took place with the appearance of the broth in the flasks.
If the broth became cloudy that meant microbes were present

21. Pasteur’s Experiment Results: Open flask – the broth became cloudy
Closed flask – the broth remain clear
Dust was observed in the neck of the S-shaped neck of the flask.

22. Pasteur’s Experiment Conclusion:
The hypothesis was supported by the data therefore it was accepted.
Because the broth did not turn cloudy and dust was observed trapped in the neck of the S-Shaped flask, it was concluded that the microbes came from cells of organisms riding on dust particles.

23. The Scientific Method
Each of these scientist used the scientific method of investigation to successfully disprove spontaneous generation.
Remember Science is not just a body of facts but a method of investigation.