INTRODUCTION

For many centuries it was believed that spontaneous generation--living things arising from nonliving things--could occur. In old books one can read of leaves falling into water and becoming fish, of a recipe for generating mice from grains of wheat and a dirty shirt, of frogs developing in the mud at the bottom of ponds or from raindrops, and many other tales that now seem amusing.

One belief was that wormlike maggots arose spontaneously from decaying meat. But Francesco Redi, an Italian doctor, suggested that maggots were the larval stage of flies and that they hatched from eggs deposited on decaying meat.  In 1668 he designed an experiment to test the hypothesis that maggots were produced spontaneously.  Redi put meat in open flasks, sealed flasks, and screen-covered flasks. Maggots developed in the open flasks only. However, on the screens of some of the flasks, flies laid eggs, which hatched into maggots.  Redi's experiment presented the first convincing evidence against spontaneous generation.

John Needham, an English scientist, was a supporter of the idea of spontaneous generation.  He designed an experiment using broth (a gravy-like material) and showed (though incorrectly) that (bacteria) would grow in a sealed flask of boiled broth.  His poor laboratory technique led to his incorrect conclusion.

Lazzaro Spallanzani, an Italian biologist, revised Needham’s experiment and showed that (bacteria) would not grow in a flask of broth that was properly boiled and sealed.  His results showed that Needham was wrong and spontaneous generation would not occur.  However, his work generated an additional hypothesis—that “air” was needed for spontaneous generation to occur and Spallanzani’s experiment did not allow for that.

Almost two hundred years later, French chemist Louis Pasteur set out to fully disprove the theory that spontaneous generation produced the bacteria found in broth exposed to the air. The bacteria supposedly came from the broth in the presence of an "active principle." The active principle could not work without air.

Pasteur, however, hypothesized that the bacteria were carried to the broth by dust particles in the air. In 1862 he devised an experi­ment that proved his hypothesis and led to the abandonment of the idea of spontaneous generation.

In this lab, Pasteur's famous experiment was recreated using more modern materials.