Spontaneous Generation and Cell Theory

The Theory of Spontaneous Generation

• Aristotle (384-322 BC):

  • Articulated the theory of spontaneous generation: life can arise from nonliving matter.
  • Proposed life arose from nonliving material containing pneuma ("vital heat").
  • Cited examples like the sudden appearance of fish in new puddles.

• Seventeenth Century:

  • Proponents of spontaneous generation noted the appearance of frogs along the Nile's muddy banks during flooding.
  • Observed mice appearing in grain stored in barns, especially when the roof leaked and grain molded.

• Jan Baptista van Helmont:

  • Proposed mice could arise from rags and wheat kernels left in an open container for 3 weeks; he mistook an ideal habitat for spontaneous generation.

• Francesco Redi (1626-1697):

  • Experiment in 1668 refuted the spontaneous generation of maggots on meat.
  • Predicted preventing flies from contacting meat would prevent maggots.
  • Experiment:
    • Meat in six containers: two open, two covered with gauze, two tightly sealed.
    • Maggots appeared in uncovered jars only and also on the gauze, not in sealed jars.
  • Conclusion: Maggots are offspring of flies, not spontaneously generated.

• John Needham (1713-1781):

  • In 1745, reported experiments boiling broth infused with plant or animal matter, then sealing the flasks.
  • Observed cloudy broth with numerous microscopic creatures after a few days.
  • Argued microbes arose spontaneously, but likely didn't boil broth enough to kill preexisting microbes.

• Lazzaro Spallanzani (1729-1799):

  • Disagreed with Needham and performed experiments using heated broth in sealed and unsealed jars.
  • Results: Heated but sealed flasks remained clear unless opened to the air, suggesting microbes came from the air.
  • Needham's counter-argument: Spallanzani's extended boiling destroyed a