Classic Experiments Disproving Spontaneous Generation

Definition: The historical belief that living organisms could arise spontaneously from non-living matter (e.g., frogs from falling rain, flies from decaying meat).
Active Principle: The hypothesized mysterious "life-force" in non-living matter or air (e.g., wheat combined with a sweaty shirt generating mice).

Initial Experiment: Placed meat into open and wax-sealed jars; maggots only developed in open containers accessible to flies.
Mesh Experiment: Used fine netting to allow air access while blocking flies. Flies laid eggs on top of the mesh, leaving the meat free of maggots.
Conclusion: Living organisms come only from pre-existing living organisms of their own kind.

Experiment: Boiled broth to kill existing organisms, sealed flasks loosely, and observed microbial growth after several days.
Conclusion: Claimed proof of spontaneous generation.
Experimental Error: Microorganisms entered from the air through loose stoppers before or after boiling.

Hermetic Sealing: Repeated Needham's work but boiled broth longer and fused glass tops shut (hermetically sealed). Resulted in zero microbial growth.
Timed Boiling Experiment: Tested broth boiled for 30, 60, 90, and 120 minutes with tight versus loose seals.
Conclusion: Extended boiling did not ruin the broth's ability to support life; microbial contamination was caused exclusively by air exposure.

Spallanzani's broth experiment showing growth in open/loosely sealed flasks vs no growth in sealed flasks

Swan-Neck Flask Design: Boiled nutrient broth in flasks with curved S-shaped necks that allowed air exchange but trapped falling dust and airborne microbes in the bend.
Results: Broth remained sterile as long as the flask remained upright. Tipping the flask allowed broth to touch the trapped dust, inducing microbial growth.
Conclusion: Fully disproved abiogenesis, demonstrating that all micro-organic growth originates from airborne contaminants.

Pasteur's swan-neck flask experiment procedure