It’s almost impossible to read a mainstream media report on cruising without encountering the phrase “floating petri dish.”

Typically, it’s used by lazy journalists to instantly convey to the reader that the ships are breeding grounds for every disease known to mankind.

The only problem? As with most stereotype-based buzzwords, it’s part of a completely false narrative.

Having had it up to here (you’re going to need to imagine us using several fingers to dramatically indicate our level of fed-upness, which is right around the top of our eyeballs) with the comparison, we decided to address the topic head-on.

So, for any supposed journalists out there preparing to use the analogy in a future piece, let us offer up this simple (and yes, humorous) explanation as to why cruise ships and petri dishes have about as much in common as a dingy and a mega-ship.

1. Cruise ships were not invented by Julius Petri

Though the title of “first cruise ship” is somewhat in dispute, with nearly every major modern cruise line laying claim to creating the cruise phenomenon in one form or another, it’s clear the first pleasure cruise took place in the late 1960s or early 1970s.

Julius Richard Petri, a German scientist, invented the dish that bears his name between 1877 and 1879. Furthermore, Petri died in 1921, making it impossible for him to have invented a cruise ship, or even to have imagined what a modern cruiseliner might look like.

2. There is practically no physical similarity between the two.

Petri dishes are typically round containers that measure 200 millimeters wide or less. Cruise ships are somewhat rectangular-shaped objects, with most averaging over 1,000 feet long (that’s 304,800 millimeters).

Petri dishes are commonly made of glass, and in the last decade or so, plastic. While cruise ships feature glass and plastic accents, the ship itself is always made of steel.

Anyone who says a cruise ship resembles a Petri dish needs to have their eyes checked.

3. Petri dishes are inexpensive

It’s possible to purchase 50 Petri dishes on Amazon.com for as little as $15.95. A cruise ship, on the other hand, costs significantly more. The closest resemblance between a petri dish and something you’ll find on a ship that’s similarly priced is a cocktail at Carnival Cruise Line’s Alchemy Bar.

Their mixologists are pretty darn close to scientists and, like what’s often grown in petri dishes, they might just have the cure for what ails you.

4. The floor of a cruise ship isn’t coated with agar

The bottom of a Petri dish is typically coated with a thin layer of agar or agarose gel and left undisturbed for a lengthy period of time to allow germs to grow.

Cruise ship floors are usually made of tile or carpet, and they’re cleaned multiple times per day.

5. Cruise ships don’t live in a lab

Petri dishes rarely leave the laboratory, where scientists spend hours conducting studies and experiments. Cruise ships, on the other hand, spend all their time exploring the world, visiting a new port every day, and as an added bonus, taking a whole lot of happy people along for the ride.

6. There’s been no significant innovation in Petri dishes since they were invented

“The Petri dish has pretty much always stayed the same – there aren’t a lot of differences that you can make,” said Andrea Sella, an award-winning chemist, broadcaster, and classic science kit and equipment enthusiast.

On the other hand, every new modern cruise ship introduces something new to the mix.

Whether it’s the go karts zipping along the upper deck on Norwegian Bliss, the BOLT roller coaster which thrills guests on Mardi Gras, or the North Star observation pod which literally takes Anthem of the Seas guests to new heights, cruise ships are constantly evolving.

7. Nobody ever trash-talks petri dishes

Talk about irony! While you constantly hear cruise ships referred to as “floating petri dishes,” you never hear petri dishes referred to as laboratory-locked cruise ships. And really, for the first analogy to work, shouldn’t the reverse also hold true? Yet in all the years we’ve been covering the cruise industry, we’ve never once heard anyone — from CEO’s of major cruise lines to passengers — make a disparaging remark about petri dishes.

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This article was originally published on December 29, 2020.