Spontaneous Generation The Experiments of Redi, Spallanzani, and Pasteur Monday, August 26th

What is Spontaneous Generation? * 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? * 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 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? * 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 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 loose 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

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? * 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 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