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This Google Doodle lets you watch gross-looking cultures of bacteria grow out of six petri dishes that take the place of Google's logo. Each dish's microbial inhabitants come from a different source: Smelly socks, a doorknob, a dish sponge.
The nastiest culture by far comes from a dog's mouth, but be warned: The computer keyboard seems to come in second place.
Ick factor of this Google Doodle aside, the petri dish was an ingeniously simple device that allowed researchers to grow and test microbes without contaminating them. The dish works by filling one side of the round, clear glass dish with agar and nutrients and covering it with its overlapping lid.
But when in action, petri dishes look like they're upside down. That's because once the agar has solidified, the dish is flipped so that the bacteria can incubate on the "ceiling" of the dish, without getting dripped on by any condensation, says "Principles of Microbiology."
According to "The Joy of Science," the device works on the same principle as Louis Pasteur's famous swan-necked flask experiment, which kept its contents sterile by blocking any bacteria from entering the container.
The petri dish was so effective that it's still in wide use today.