You’ll Be Amazed to Know That ...

39. Only one in ten cells in your body is actually human.

Of the 100 trillion cells in our bodies, the majority are microorganisms such as bacteria and viruses. In fact, the National Institutes of Health Human Microbiome Project found that microorganisms make up about 1 to 3 percent of the body’s mass, or as much as six pounds of bacteria in a 200-pound adult.

40. Your salivary glands produce one to two quarts of spit every day.

Saliva breaks down food and keeps the mouth infection-free. Plus, without saliva, you wouldn’t be able to taste anything! Food molecules need to dissolve in saliva for taste buds to recognize them.

41. You might be missing an arm muscle.

About 86 percent of us have a palmaris longus muscle running from the elbow to the palm. To test whether you have it, touch your pinkie to your thumb and tighten your wrist muscles; a tendon connected to the muscle will pop out in the center of your wrist, below your palm. In humans, it helps wrist flexibility, but there’s no consequence if you’re born without one. Scientists aren’t sure why some people have the muscle and others don’t, but they think that it probably helped our primate ancestors grip and swing through trees.

42. Your heart can pump one million barrels of blood in a lifetime.

Meanwhile, your kidneys filter your entire supply of blood more than 30 times every day. The average adult has 4.8 to 6 quarts of blood, and the kidneys filter about half a cup per minute.

43. Your skeleton contains a lot of water.

The human body is mostly water (55 and 60 percent for women and men, respectively). But that fluid isn’t just in your skin, muscles, and organs—it’s in your skeleton too. In fact, water makes up nearly a third of your bone mass.

44. The longest muscle in your body is named after a tailor.

The name comes from sartor, the Latin word for tailor. Tailors used to sit cross-legged on the floor when they pinned hems or cuffs. That position required heavy use of the sartorius muscle, which ropes around your thigh from the pelvis to the shinbone.

45. Your lungs have an enormous surface area.

Tiny air sacs called alveoli allow oxygen and carbon dioxide to move between the lungs and the bloodstream. Average adult lungs have about 480 million alveoli, the surface area of which could cover half a tennis court.

46. The average human passes about 360 pounds of poop per year.

Before you get grossed out, consider this medical wonder: A fecal transplant to help someone with an infection called Clostridium difficile—in which doctors take a healthy person’s poop and put it into the sufferer’s gastrointestinal tract—has a 90 percent cure rate. That’s a higher rate than for treatment with an antibiotic.

47. You might be able to wiggle your ears.

Thirty million years ago, the three auricular muscles of the outer ear helped our evolutionary ancestors pivot their ears the way cats do. This movement doesn’t serve much purpose to modern humans—other than as a party trick. Scientists aren’t sure why, but only about 10 to 20 percent of us are able to engage those muscles to wiggle our ears.

48. You can live without your stomach ...

With some weight-loss surgeries and for some stomach cancers, patients might have part or all of their stomach removed. Once it is gone, surgeons will connect the esophagus directly to the small intestine so food can be digested there.

49. ... and without your colon.

The large intestine might be removed to treat colorectal cancer, Crohn’s disease, or ulcerative colitis. A surgeon would either connect a pouch made of small intestine to your anus so you can pass stools or divert waste from the small intestine to an opening created in the abdomen, which would empty into a colostomy bag outside the body.

50. Your skin glows in the dark.

A decade ago, Japanese scientists used ultrasensitive cameras to discover that humans actually give off light, sort of like fireflies. Chemical reactions within our cells transmit a glow, mostly from the forehead, cheeks, and neck. The glow is faintest late at night and brightest in late afternoon, possibly because of changes in metabolism.