The Body: A Guide for Occupants

by Bill Bryson

carbon, oxygen, hydrogen, nitrogen, calcium, and phosphorus—account for 99.1 percent of what makes us,

The reason we are not light and bouncy like a balloon is that the oxygen is mostly bound up with hydrogen (which accounts for another 10 percent of you) to make water—and water, as you will know if you have ever tried to move a wading pool or just walked around in really wet clothes, is surprisingly heavy. It is a little ironic that two of the lightest things in nature, oxygen and hydrogen, when combined form one of the heaviest, but that’s nature for you.

you blink fourteen thousand times a day—so much that your eyes are shut for twenty-three minutes of every waking day.

Every cell in your body (strictly speaking, every cell with a nucleus) holds two copies of your DNA. That’s why you have enough to stretch to Pluto and beyond.

DNA exists for just one purpose—to create more DNA.

The formal name for the skin is the cutaneous system. Its size is about two square meters (approximately twenty square feet), and all told your skin will weigh somewhere in the region of ten to fifteen pounds, though much depends, naturally, on how tall you are and how much buttock and belly it needs to stretch across.

Curiously, we don’t have any receptors for wetness. We have only thermal sensors to guide us, which is why when you sit down on a wet spot, you can’t generally tell whether it really is wet or just cold.

“Melanin is a superb natural sunscreen,”

grow about twenty-five feet of hair in a lifetime,

Your sweat is 99.5 percent water. The rest is about half salt and half other chemicals. Although salt is only a tiny part of your overall sweat, you can lose as much as three teaspoonfuls of it in a day in hot weather, which can be a dangerously high amount, so it is important to replenish salt as well as water.

To make one’s hands safely clean after a medical examination requires thorough washing with soap and water for at least a full minute—a

A full minute!

TAKE A DEEP breath. You probably suppose that you are filling your lungs with rich, life-giving oxygen. Actually, not really. Eighty percent of the air you breathe is nitrogen.

“From the 1950s through the 1990s,” he says, “roughly three antibiotics were introduced into the U.S. every year. Today it’s roughly one new antibiotic every other year. The rate of antibiotic withdrawals—because they don’t work anymore or have become obsolete—is twice the rate of new introductions. The obvious consequence of this is that the arsenal of drugs we have to treat bacterial infections has been going down. There is no sign of it stopping.” What makes this much worse is that a great deal of our antibiotic use is simply crazy. Almost three-quarters of the forty million antibiotic prescriptions written each year in the United States are for conditions that cannot be cured with antibiotics. According to Jeffrey Linder, professor of medicine at Northwestern University, antibiotics are prescribed for 70 percent of acute bronchitis cases, even though guidelines explicitly state that they are of no use there.

Even more appallingly, in the United States 80 percent of antibiotics are fed to farm animals, mostly to fatten them. Fruit growers can also use antibiotics to combat bacterial infections in their crops. In consequence, most Americans consume secondhand antibiotics in their food (including even some foods labeled as organic) without knowing it.

The brain exists in silence and darkness, like a dungeoned prisoner. It has no pain receptors, literally no feelings.

Your brain is you. Everything else is just plumbing and scaffolding.

Just sitting quietly, doing nothing at all, your brain churns through more information in thirty seconds than the Hubble Space Telescope has processed in thirty years.

The brain is often depicted as a hungry organ. It makes up just 2 percent of our body weight but uses 20 percent of our energy.

In a similar way, the brain manufactures all the components that make up our senses. It is a strange, nonintuitive fact of existence that photons of light have no color, sound waves no sound, olfactory molecules no odors. As James Le Fanu has put it, “While we have the overwhelming impression that the greenness of the trees and the blueness of the sky are streaming through our eyes as through an open window, yet the particles of light impacting on the retina are colourless, just as the waves of sound impacting on the eardrum are silent and scent molecules have no smell. They are all invisible, weightless, subatomic particles of matter travelling through space.” All the richness of life is created inside your head. What you see is not what is but what your brain tells you it is, and that’s not the same thing at all.

color isn’t a fixed reality but a perception.

We consume about two and a half quarts of water a day, though we are not generally aware of it because about half is contained within our foods.