Question

what were the limitations to the experiment on spontaneous generation theory by lazzaro spallanzani and John needham

Answer 1

Ans.  John Needham give a report of his own experiments, in which he briefly boiled broth infused with plant or animal matter, hoping to kill all preexisting microbes.He then sealed the flasks. After a few days, Needham observed that the broth had become cloudy and a single drop contained numerous microscopic creatures. He argued that the new microbes must have arisen spontaneously. In reality, however, he likely did not boil the broth enough to kill all preexisting microbes.

Lazzaro Spallanzani did not agree with Needham’s conclusions, however, and performed hundreds of carefully executed experiments using heated broth.As in Needham’s experiment, broth in sealed jars and unsealed jars was infused with plant and animal matter. Spallanzani’s results contradicted the findings of Needham: Heated but sealed flasks remained clear, without any signs of spontaneous growth, unless the flasks were subsequently opened to the air. This suggested that microbes were introduced into these flasks from the air. In response to Spallanzani’s findings, Needham argued that life originates from a “life force” that was destroyed during Spallanzani’s extended boiling. Any subsequent sealing of the flasks then prevented new life force from entering and causing spontaneous generation .

Needham who claimed these had arisen through spontaneous generation. His experiment was contested for the fact he did not heat the broth for long enough and his animacules were heat resistant.

Needham’s response claimed that air was necessary for spontaneous generation and that the “vital heat” in the air had been destroyed during Spallanzani’s experiment.