Question

When John Tyndall attempted to repeat Louis Pasteur’s experiment using the flask shown below, he found that microbial growth sometimes occurred even when the growth medium was boiled for an extended time. Explain why he obtained results that conflicted with Pasteur’s results.

Answer 1

Louis Pasteur's 1859 experiment is widely seen as having settled the question of spontaneous generation. He boiled a meat broth in a swan neck flask. The bend in the neck of the flask 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

The investigations of John Tyndall, a correspondent of Pasteur and a great admirer of Pasteur's work, were decisive in disproving spontaneous generation and dealing with lingering issues. Still, even Tyndall encountered difficulties in dealing with the effects of microbial spores which were not well understood in his day. Like Pasteur, he boiled his cultures to sterilize them, and some types of bacterial spores can survive boiling.

The autoclave, which eventually came into universal application in medical practice and microbiology to sterilise equipment, was not an instrument that had come into use at the time of Tyndall's experiments.

Endospores are a resistant, dormant, survival form of bacteria. They are resistant to high temperatures, most disinfectants, low level radiation and drying. While significantly resistant to heat and radiation, endospores can be destroyed by burning or by autoclaving at a temperature exceeding the boiling point of water, 100 °C. Endospores are able to survive at 100 °C for hours, although the larger the number of hours the fewer that will survive.

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