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The Beginning of Spontaneous Generation
The concept of spontaneous generation: "some life forms arose spontaneously from non-living things"
Sarted from the Ancient Romans, through the Middle Ages, until the late nineteenth century. -
Francesco Redi
--Italian physician and poet
--First attempt to disprove SG concept by disproving that maggots rose form rotting meat.
--Hypothesis: "maggots developed form eggs laid by flies"
--Experiment: put meat in a variety of flasks (open to the air, sealed, covered with gauze)
--Observation: maggots only appeared in open flasks
--Principle: flies could only reach those meats to lay their eggs -
Microscopy
Invention of microscopy revealed a "whole new world of organisms that appeared ot arise spontaneously". "Animalcules" (organisms) could be created by putting hay in water and waiting for a few days before examining it under the microscope. -
Recipe for mice created
Recipe: place sweaty underwear and husks of wheat in an open-mouthed jar, then wait for 21 days.
Principle: the sweat would penetrate and change the wheat into mice -
John Needham
John Needham, an English clergyman initiated the second attack on the SG concept. At that time people already knew that boiling killed microorganisms. So he conducted an experiment where he boiled chicken broth, put it in a flask and then sealed it and waited. However, microorganisms still grew. -
Lazzaro Spallanzani
Spallanzani suggested that for Needham's experiment, microorganisms entered the broth from the air after the broth was boiled and before the flask was sealed. He modified the experiment by placing the chicken broth into a flask, sealed it and the made it partial vaccumed, finally, he boiled the broth. The result was that no microorganisms grew.
He proved that spontaneous generation could not occur without air. -
Louis Pasteur
By using a variation of methods of Needham and Spallanzani's experiments, finally defeated the SG concept.
Experiment #1: boiled meat broth in a flask, heated the neck of the flask in a flame to bend it into an "S" shape, so air coul enter but microorganisms would get stuck at the bottom of the curve.
Observation: no microorganisms grew -
Louis Pasteur (continued)
Experiment #2: afterwards tilt the flask so the broth touches the bottome of the curve where microorganisms settled
Observation: broth became cloudy (microorganisms grew)
Pasteur had "refuted the SG theory and demonstrated that microorganisms existed everywhere (including the air)".
