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12 Unusual Measurements for International Metrology Day

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For most of human history, systems of weights and measurement have varied widely between lands, and there was rarely a simple conversion from one system to another. Systems of measurement often spread only by imperial conquest—from that spread, the standard system used by the British Empire (the Imperial system) became the most commonly used, but it was not alone.

During the scientific revolution, the need for a standardized system was recognized, and governments concurred that trade would be simplified with the same units of measurement used by all sides. The standardization of measurement was a long process, beginning in the late 18th century, but on May 20, 1875, the first Diplomatic Treaty of the Metre was signed by seventeen countries (including the United States, who maintains a good standing with the Metre Convention to this day, despite its attempt to metricate in the 1970s being a rather stunning failure), affirming the standard arbitrary measurements put forth by the document. Every year since the centennial of the Metre Convention, May 20 has been celebrated as International Metrology Day

The international system of units (the metric system, or SI) is based off of six basic units—the second (time), metre (length), Kelvin (temperature), kilogram (mass), ampere (electric current), candela (luminous intensity), and the mole (amount of substance). All countries use the metric system to some significant degree, aside from the United States, Burma, and Liberia. However, that doesn’t mean that there aren’t other odd and arbitrary units of measurement out there. John Green covered 36 of these units on the recent mental_floss video.

The theme of this year’s Metrology Day celebrations is “Metrology in Daily Life,” and here are 12 measurements you probably don’t notice as you go about your day.

1. Your body only contains about 5.5 liters of blood, but your heart cycles over 7500 liters of blood (around 2000 U.S. gallons) through it each day. That’s enough to fill almost 48 oil barrels.

2. Humans shed around 500 million skin cells a day, adding up to 0.003 oz of skin each hour, 0.072 oz per day, and almost 26.3 oz of cells every year. It takes four to five large bananas to comprise the same weight.

3. The mucous membranes in your head produce between 1 and 1.5 liters of mucus a day. Thankfully, most of that drains directly down the back of your throat, unnoticed. When you’re sick, you generally don’t produce more of it, but it’s more noticeable because its consistency has changed.

4. Each day, the average adult—male or female—speaks about 16,000 words.

5. You probably lose around 100 hairs from your head every day, which can sound like a lot, but the average blonde has 150,000 hairs on their head. Brunettes, with brown or black hair, range around 100,000, and redheads, while last, still have over 80,000 hairs covering the scalp.

6. Each hair stays on your scalp for between 2 and 6 years, and is growing for all but approximately the last 3 months of its “lifespan.”

7. The average American eats around 2000 pounds (900 kg) of food per year (or almost 5.5 pounds (2.5 kg) of food per day). The 1968 VW Beetle weighed in similarly.

8. Helping to digest that food are between 600 and 5000 distinct species of bacteria living in the healthy human gut. All of those species add up to over 100 trillion bacterial cells in the body, outnumbering “human” cells 10-to-1. Don’t worry, you’re not completely bacteria. Those single-celled organisms generally weigh less than 5 pounds (2.3 kg).

9. The human skeleton makes up about 18 percent of our weight (around 32 pounds, or 15 kg in a 180 pound/81 kg person), and can support five times as much pressure as a steel bar with the same dimensions. Frequently-used bones (such as the femur in a runner, or the arm bones in a tennis player) can support up to 8 times as much pressure as a steel bar with the same dimensions.

10. Want to make those bones stronger? Brisk walking can significantly strengthen the lower limbs for those whose current activity level falls around the U.S. average—less than 6000 steps taken every day. While no industrialized country surpasses the ideal average of 10,000 steps per day, Australians come closest, with a 9965-step average in the sample group.

11. Working out works our sweat glands out, too! The human body sweats an average of 1.5 L/hour during physical exertion, but can sweat up to 3 L/hour if extremely taxed or in high temperatures at the same time. A sedentary person in a comfortable environment isn’t sweat-free, though—every day still brings about 1 L of sweat, with more than half a pint of it coming from the feet alone!

12. Humans blink around 10 to 15 times a minute, with each blink lasting around 100 milliseconds. This adds up to almost 16 minutes of the day spent blinking, assuming one sleeps 8 hours a night.

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Live Smarter
8 Tricks to Help Your Cat and Dog to Get Along
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When people aren’t debating whether cats or dogs are more intelligent, they’re equating them as mortal foes. That’s a stereotype that both cat expert Jackson Galaxy, host of the Animal Planet show My Cat From Hell, and certified dog trainer Zoe Sandor want to break.

Typically, cats are aloof and easily startled, while dogs are gregarious and territorial. This doesn't mean, however, that they can't share the same space—they're just going to need your help. “If cats and dogs are brought up together in a positive, loving, encouraging environment, they’re going to be friends,” Galaxy tells Mental Floss. “Or at the very least, they’ll tolerate each other.”

The duo has teamed up in a new Animal Planet series, Cat Vs. Dog, which airs on Saturdays at 10 p.m. The show chronicles their efforts to help pet owners establish long-lasting peace—if not perfect harmony—among cats and dogs. (Yes, it’s possible.) Gleaned from both TV and off-camera experiences, here are eight tips Galaxy and Sandor say will help improve household relations between Fido and Fluffy.


Contrary to popular belief, certain breeds of cats and dogs don't typically get along better than others. According to Galaxy and Sandor, it’s more important to take their personalities and energy levels into account. If a dog is aggressive and territorial, it won’t be a good fit in a household with a skittish cat. In contrast, an aging dog would hate sharing his space with a rambunctious kitten.

If two animals don’t end up being a personality match, have a backup plan, or consider setting up a household arrangement that keeps them separated for the long term. And if you’re adopting a pet, do your homework and ask its previous owners or shelter if it’s lived with other animals before, or gets along with them.


To set your dog up for success with cats, teach it to control its impulses, Sandor says. Does it leap across the kitchen when someone drops a cookie, or go on high alert when it sees a squeaky toy? If so, it probably won’t be great with cats right off the bat, since it will likely jump up whenever it spots a feline.

Hold off Fido's face time with Fluffy until the former is trained to stay put. And even then, keep a leash handy during the first several cat-dog meetings.


Cats need a protected space—a “base camp” of sorts—that’s just theirs, Galaxy says. Make this refuge off-limits to the dog, but create safe spaces around the house, too. This way, the cat can confidently navigate shared territory without trouble from its canine sibling.

Since cats are natural climbers, Galaxy recommends taking advantage of your home’s vertical space. Buy tall cat trees, install shelves, or place a cat bed atop a bookcase. This allows your cat to observe the dog from a safe distance, or cross a room without touching the floor.

And while you’re at it, keep dogs away from the litter box. Cats should feel safe while doing their business, plus dogs sometimes (ew) like to snack on cat feces, a bad habit that can cause your pooch to contract intestinal parasites. These worms can cause a slew of health problems, including vomiting, diarrhea, weight loss, and anemia.

Baby gates work in a pinch, but since some dogs are escape artists, prepare for worst-case scenarios by keeping the litter box uncovered and in an open space. That way, the cat won’t be cornered and trapped mid-squat.


“People exercise their dogs probably 20 percent of what they should really be doing,” Sandor says. “It’s really important that their energy is released somewhere else so that they have the ability to slow down their brains and really control themselves when they’re around kitties.”

Dogs also need lots of stimulation. Receiving it in a controlled manner makes them less likely to satisfy it by, say, chasing a cat. For this, Sandor recommends toys, herding-type activities, lure coursing, and high-intensity trick training.

“Instead of just taking a walk, stop and do a sit five times on every block,” she says. “And do direction changes three times on every block, or speed changes two times. It’s about unleashing their herding instincts and prey drive in an appropriate way.”

If you don’t have time for any of these activities, Zoe recommends hiring a dog walker, or enrolling in doggy daycare.


In Galaxy's new book, Total Cat Mojo, he says it’s a smart idea to let cats and dogs sniff each other’s bedding and toys before a face-to-face introduction. This way, they can satisfy their curiosity and avoid potential turf battles.


Just like humans, cats and dogs have just one good chance to make a great first impression. Luckily, they both love food, which might ultimately help them love each other.

Schedule the first cat-dog meeting during mealtime, but keep the dog on a leash and both animals on opposite sides of a closed door. They won’t see each other, but they will smell each other while chowing down on their respective foods. They’ll begin to associate this smell with food, thus “making it a good thing,” Galaxy says.

Do this every mealtime for several weeks, before slowly introducing visual simulation. Continue feeding the cat and dog separately, but on either side of a dog gate or screen, before finally removing it all together. By this point, “they’re eating side-by-side, pretty much ignoring each other,” Galaxy says. For safety’s sake, continue keeping the dog on a leash until you’re confident it’s safe to take it off (and even then, exercise caution).


After you've successfully ingratiated the cat and dog using feeding exercises, keep their food bowls separate. “A cat will walk up to the dog bowl—either while the dog’s eating, or in the vicinity—and try to eat out of it,” Galaxy says. “The dog just goes to town on them. You can’t assume that your dog isn’t food-protective or resource-protective.”

To prevent these disastrous mealtime encounters, schedule regular mealtimes for your pets (no free feeding!) and place the bowls in separate areas of the house, or the cat’s dish up on a table or another high spot.

Also, keep a close eye on the cat’s toys—competition over toys can also prompt fighting. “Dogs tend to get really into catnip,” Galaxy says. “My dog loves catnip a whole lot more than my cats do.”


Socializing these animals at a young age can be easier than introducing them as adults—pups are easily trainable “sponges” that soak up new information and situations, Sandor says. Plus, dogs are less confident and smaller at this stage in life, allowing the cat to “assume its rightful position at the top of the hierarchy,” she adds.

Remain watchful, though, to ensure everything goes smoothly—especially when the dog hits its rambunctious “teenage” stage before becoming a full-grown dog.

10 Juicy Facts About Sea Apples

They're both gorgeous and grotesque. Sea apples, a type of marine invertebrate, have dazzling purple, yellow, and blue color schemes streaking across their bodies. But some of their habits are rather R-rated. Here’s what you should know about these weird little creatures.


The world’s oceans are home to more than 1200 species of sea cucumber. Like sand dollars and starfish, sea cucumbers are echinoderms: brainless, spineless marine animals with skin-covered shells and a complex network of internal hydraulics that enables them to get around. Sea cucumbers can thrive in a range of oceanic habitats, from Arctic depths to tropical reefs. They're a fascinating group with colorful popular names, like the “burnt hot dog sea cucumber” (Holothuria edulis) and the sea pig (Scotoplanes globosa), a scavenger that’s been described as a “living vacuum cleaner.”


Sea apples have oval-shaped bodies and belong to the genus Pseudocolochirus and genus Paracacumaria. The animals are indigenous to the western Pacific, where they can be found shuffling across the ocean floor in shallow, coastal waters. Many different types are kept in captivity, but two species, Pseudocolochirus violaceus and Pseudocolochirus axiologus, have proven especially popular with aquarium hobbyists. Both species reside along the coastlines of Australia and Southeast Asia.


Sea cucumbers, the ocean's sanitation crew, eat by swallowing plankton, algae, and sandy detritus at one end of their bodies and then expelling clean, fresh sand out their other end. Sea apples use a different technique. A ring of mucus-covered tentacles around a sea apple's mouth snares floating bits of food, popping each bit into its mouth one at a time. In the process, the tentacles are covered with a fresh coat of sticky mucus, and the whole cycle repeats.


Sea apples' waving appendages can look delicious to predatory fish, so the echinoderms minimize the risk of attracting unwanted attention by doing most of their feeding at night. When those tentacles aren’t in use, they’re retracted into the body.


The rows of yellow protuberances running along the sides of this specimen are its feet. They allow sea apples to latch onto rocks and other hard surfaces while feeding. And if one of these feet gets severed, it can grow back.


Sea apples are poisonous, but a few marine freeloaders capitalize on this very quality. Some small fish have evolved to live inside the invertebrates' digestive tracts, mooching off the sea apples' meals and using their bodies for shelter. In a gross twist of evolution, fish gain entry through the back door, an orifice called the cloaca. In addition expelling waste, the cloaca absorbs fresh oxygen, meaning that sea apples/cucumbers essentially breathe through their anuses.


Most full-grown adult sea apples are around 3 to 8 inches long, but they can make themselves look twice as big if they need to escape a threat. By pulling extra water into their bodies, some can grow to the size of a volleyball, according to Advanced Aquarist. After puffing up, they can float on the current and away from danger. Some aquarists might mistake the robust display as a sign of optimum health, but it's usually a reaction to stress.


Sea apples use their vibrant appearance to broadcast that they’re packing a dangerous toxin. But to really scare off predators, they puke up some of their own innards. When an attacker gets too close, sea apples can expel various organs through their orifices, and some simultaneously unleash a cloud of the poison holothurin. In an aquarium, the holothurin doesn’t disperse as widely as it would in the sea, and it's been known to wipe out entire fish tanks.


These invertebrates reproduce sexually; females release eggs that are later fertilized by clouds of sperm emitted by the males. As many saltwater aquarium keepers know all too well, sea apple eggs are not suitable fish snacks—because they’re poisonous. Scientists have observed that, in Pseudocolochirus violaceus at least, the eggs develop into small, barrel-shaped larvae within two weeks of fertilization.


Syzgium grande is a coastal tree native to Southeast Asia whose informal name is "sea apple." When fully grown, they can stand more than 140 feet tall. Once a year, it produces attractive clusters of fuzzy white flowers and round green fruits, perhaps prompting its comparison to an apple tree.


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