- Louis Pasteur designed an experiment to test whether sterile nutrient broth could spontaneously generate microbial life. To do this, he set up two experiments. In both, Pasteur added nutrient broth to flasks, bent the necks of the flasks into S shapes, and then boiled the broth to kill any existing microbes.
- After the broth had been sterilized, Pasteur broke off the swan necks from the flasks in Experiment 1, exposing the nutrient broth within them to air from above. The flasks in Experiment 2 were left alone.
- Over time, dust particles from the air fell into the broken flasks of Experiment 1. In Experiment 2, dust particles remained near the tip of the swan necks, but could not travel against gravity into the flasks, keeping the nutrient broth sterile.
- The broth in the broken flasks quickly became cloudy–a sign that it teemed with microbial life. However, the broth in the unbroken flasks remained clear. Without the introduction of dust–on which microbes can travel–no life arose. Thus, the Louis Pasteur experiment refuted the notion of spontaneous generation.
Try it at Home
With a few simple items, you can try the same spontaneous generation experiment at home.
Jars with Lids
- Slice up an apple and put a few pieces in each of 3 jars.
- Put a lid tightly on one jar.
- Put some cheesecloth on top of another jar, securing it with a couple of rubber bands.
- Leave the third jar uncovered.
- Set the jars out in an open area for a couple of days.
You may notice no flies or maggots on the jar with the lid, some flies or maggots on top of the cheesecloth (not inside the jar), and even some maggots or flies inside the open jar.
What does this experiment prove? Did your results match Francesco Redi’s spontaneous generation experiment?