IRA FLATOW, HOST:
It's time for our monthly episode of Science Diction, where we explore the origins of scientific words with my guest Howard Markel, professor of history of medicine at the University of Michigan in Ann Arbor, also director of the Center for the History of Medicine there. He joins us WUOM. Welcome back, Howard.
HOWARD MARKEL: Good afternoon, Ira.
FLATOW: We have a very interesting word, or actually lab equipment today.
MARKEL: That we do. It's my favorite plate. It's the Petri dish.
FLATOW: The Petri dish. How did that get started?
MARKEL: Yeah. Well, it was designed by a guy named Petri - Julius Richard Petri, to be exact. He was a military physician. He worked for the German army. And in 1877, he found himself assigned to the Imperial Health Office in Berlin, which was a laboratory ran by Robert Koch. Now, Robert Koch was the Kaiser of bacteriology. He discovered the cause of cholera and tuberculosis and anthrax. So it was sort of like being a bush leaguer suddenly called up to play short stop for the Yankees.
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MARKEL: And in order for Koch to make his discoveries, he had to figure out how to grow not only lots of bacteria, but grow them in a reliable, pure culture technique. And that was a big problem, because a lot of the earlier methods were opened to the air. And, you know, a lot of other germs would join on to the media and grow. And you wouldn't really know what you were dealing with. Some were grown in test tubes. Some were grown in liquor glasses. But...
FLATOW: By the way, it would seemed like it's a no-brainer to come up with a little piece of glass, you put another piece of glass on top, and you've sealed it off.
MARKEL: It does, doesn't it? But one of the earlier ways to prevent things from getting in, we - the bacteriology term is schmutz, by the way. But one way to get it from coming in...
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MARKEL: ...was to put a heavy glass bell jar on a glass plate that had some gelatin with bacteria growing. But that was very cumbersome. You know, a bell jar is very heavy, and you're manipulating with one hand. And you've got to get to the microscope and so and so.
FLATOW: Right. And you can't put them under the microscope to look through it, either.
MARKEL: No, you can't. And that's where Petri comes in. He actually designed - familiar to every one who's listening - that glass, flat dish with a cover that fits right over it. And that was terrific, because not only could you keep contaminants from getting in, but you could slide it under the microscope, put it right on the stage of the microscope and view your specimens.
FLATOW: Mm-hmm. And has it change very much since those...
MARKEL: Not really. I mean, it's - some are made out of glass, some are made out of polyacrylic or plastic, but it's essentially the same as when Petri wrote his only - it's a 300-word paper that he wrote describing the plating technique.
FLATOW: And so the Petri dish is basically an old instrument that did its job well, and remains the same way it used to look.
MARKEL: Right. And, you know, we don't really always know who Petri is. But we do know what a Petri dish is, don't we?
FLATOW: And now we know who he is, thanks to you, Howard.
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FLATOW: Have a good holiday. Thanks for joining us.
MARKEL: Happy Holiday to you, Ira.
FLATOW: Howard Markel is professor of history of medicine at the University of Michigan in Ann Arbor, and director of the Center for the History of Medicine there. Transcript provided by NPR, Copyright NPR.