Spontaneous Generation
The Experiments of
Redi, Spallanzani, and Pasteur
Monday, August 26th
What is Spontaneous Generation?
• For MUCH of history, people believed:
– Frogs developed from falling drops of rain
– Mice arose from sweaty underwear
• This is called abiogenesis or spontaneous generation
– Living things “come” from non living material
*
One of the first “theories” of spontaneous
generation…
• Living mice could be generated spontaneously from
wheat and a sweaty shirt
– The wheat =nutritive power
– The shirt = active principle
• The active principle = a mysterious “life-force” that
allowed spontaneous generation to occur.
1668 - Francisco Redi attempted to disprove spontaneous
generation.
What was Redi’s Experiment?
• When he did it:
– 1668
• What he did:
– Put dead snakes, eels, and veal in glass jars
– Sealed one set with wax; the other remained
open
*
What was Redi’s Experiment?
• What he found:
– Uncovered meat was covered with maggots
– Sealed meat had no maggots
• What he determined:
– Wax sealed jars failed to produce maggots because
flies were unable to reach the meat
*
Why was Redi not believed?
• He has “too many variables”
• There is a lack of access and a
lack of air
• We ALL know that everything
needs air
– So of course no flies grew!
• He hadn’t proven anything
*
Redi part 2 – His response to critics
Fine mesh allows in
air, but not flies
Flies laid eggs on top of mesh
no maggots in meat
What was Redi’s conclusions?
• “All living beings come from seeds of the
plants or animals themselves”
• However, if someone were to demonstrate
even 1 exception to this hypothesis, then
Redi’s hypothesis would be rejected.
• Redi’s Experiment
1768 - Spallanzani
What was Spallanzani’s Experiment?
• When he did it:
– 1768
• What he did:
– 1st experiment
– Boiled flasks with broth (chopped hay in water)
– Sealed the flasks after boiling (airtight)
• What he found:
– There was NO bacterial growth in the flasks with
airtight seals
*
What was Spallanzani’s Experiment?
• What he did in response to critics:
– 2nd experiment
– Timed boilings
– Left some partially sealed, others airtight sealed
• What he found:
– There STILL was no bacterial growth in the flasks
that were sealed
*
What was Spallanzani’s Experiment?
tight seal
• What he
determined:
– Boiling did NOT
damage broth’s
ability to support
life
– Growth
depended on the
SEAL only
30 mins
60 mins
90 mins
120 mins
*
loose seal
Critics of Spallanzani’s Experiment
• He boiled it TOO LONG
• He spoiled the vegetative power by boiling
• He killed the ability of the broth to give life
• Life can still come from broth, BUT the broth
must not be “damaged” by boiling
What was Pasteur’s Experiment?
• When he did it:
– 1859
• What he did:
– Used swan-necked flasks
– Flasks allowed in air, but trapped dust (and microbes) in the
curve because they couldn’t overcome gravity
– Boiled broth to force the air out
– Broke the necks off of some of the curved flasks
*
What was Pasteur’s Experiment?
*
• What he found:
– NO growth occurred in the flasks with the curved necks, even
after weeks
– After 1 year, he broke off the curved necks and within a few
days, the broth became cloudy
• What he determined:
– The “active principle” was not damaged through boiling
– The AIR contained MICROBES
1859– Louis Pasteur