Spontaneous Generation The rise of the Experimental method

Aristotle (384 BC – 322 BC)  Greek philosopher, student of Plato and teacher of Alexander the Great.  His writings in the natural and physical sciences formed the basis of scientific thought for nearly 2,000 years).  His writings also influenced the theological thinking in the Islamic, Jewish and Christian theologies.  Only about a third of his writings have survived.  He applied logic to his observations, but did not use experimentation of measurement.

Spontaneous Generation  Is the idea that living things can arise from non-living material.  Or, living things of one species can arise from different species.  According to Aristotle living things came from non-living things because the nonliving material contained “vital heat”.  Clams and scallops formed in sand, oysters in slime and barnacles and limpets in rocks.  Note the Scallop, the blue dots are its “eyes”!

Beliefs  Barnacle Geese came from Barnacles.  Seeds and straw turned into mice.  Rotting meat turned into flies.  Shakespeare – snakes and crocodiles forming from the mud of the Nile.  Tapeworms arise from the bodies of their hosts.  A Barnacle goose ( Branta leucopsis)

Disproving Spontaneous generation  1668 Francisco Redi challenged the idea that rotting meat produced maggots.  He placed meat in sealed, gauze covered and open containers.  He observed maggots in the open and parially opened containers, but no maggots on the sealed container, though there were some on the mesh.  This experiment had great influence throughout Europe.

John Needham  The experiments consisted of briefly boiling a broth mixture.  The mixture was then cooled in an open container to room temperature.  Later, the flasks would be sealed, and microbes would grow a few days later.  Those experiments seemed to show that there was a life force that produced spontaneous generation.

Lazzaro Spallanzi  Modified Spallanzani’s experiment.  Boiled the broth for an hour.  Partially evacuated the jars and sealed the vessels right after boiling.  No growth was observed.  Some felt that air was necessary for spontaneous generation to occur.

Louis Pasteur  He boiled a meat broth in a flask that had a long neck that curved downward, like a goose.  The bend in the neck prevented falling particles from reaching the broth, while still allowing the free flow of air.  The flask remained free of growth for an extended period. (over a year!)  When the flask was turned so that particles could fall down the bends, the broth quickly became clouded.