THE CONFLICT OVER SPONTANEOUS GENERATION-1

• Spontaneous generation—living organisms could develop from nonliving matter.
• Aristotle (384–322 B.C.) thought some simpler invertebrates arise by spontaneous generation.

Francesco Redi

• Italian physician Francesco Redi(1626–1697), who carried out a series of experiments on decaying meat and its ability to produce maggots spontaneously.
• Redi placed meat in three containers.
• One was uncovered,
• Second was covered with paper, and 
• Third was covered with a fine gauze would exclude flies.
• Flies laid their eggs on uncovered meat and maggots developed.
• Other two pieces of meat did not produce maggots spontaneously.
• Flies were attracted to gauze-covered container and laid their eggs on the gauze; eggs produced maggots.
• Thus,Generation of maggots by decaying meat resulted from presence of fly eggs, and meat did not spontaneously generate maggots as previously believed.
• Similar experiments,others helped discredited the theory for
  larger organisms. 
  
• Discovery of microorganisms renewed by scientist "Antony van Leeuwenhoek".
• Some proposed that larger organisms didnot arose by spontaneous generation even through microorganisms.
• Microorganisms after sitting for a while,would give rise to   boiled extracts of hay or meat.

John Needham 

• In 1748, English priest John Needham (1713–1781) reported the results of his experiments on spontaneous generation.
• Needham boiled mutton broth  and then tightly stoppered the flasks.
• Many of  flasks became cloudy and contained microorganisms.
• He thought organic matter contained a vital force that could confer properties of life on nonliving matter.

Lazzaro Spallanzani 

• A few years later,  Italian priest and naturalist Lazzaro Spallanzani (1729–1799) improved on Needham’s experimental designed first sealing glass flasks that
  contained water and seeds. 
  
• Sealed flasks were placed in boiling water for 3/4 of an hour, no growth took place as long as  flasks remained sealed.
• He proposed that in the medium, air carried germs to the culture medium,and external air might be required for growth of animals.
• Supporters of spontaneous generation maintained heating and the air must be sealed in flasks to destroy its ability to support life.

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