The Body: A Guide for Occupants

by Bill Bryson

Similarly, Cryptococcus gattii was for decades known to exist in British Columbia in Canada, mostly on trees or in the soil around them, but it never harmed a human. Then, in 1999, it developed a sudden virulence, causing serious lung and brain infections among a scattering of victims in western Canada and the United States. Exact figures are impossible to come by because the disease is often misdiagnosed and, remarkably, is not reportable in California, one of the main sites of occurrence, but

From a human health perspective, the most notable protists are those from the genus Plasmodium. They are the evil little creatures that transfer from mosquitoes into us and give us malaria. Protists are also responsible for toxoplasmosis, giardiasis, and cryptosporidiosis.

contained a stretch of sixty-two letters that has been found in all living things since the dawn of creation, making it not only arguably alive but as ancient as anything else on Earth.*2 Birtles named the new virus mimivirus, for “microbe-mimicking.” When Birtles and his colleagues wrote up their findings, they couldn’t at first find any journal that would publish them, because they were too bizarre. The cooling tower was knocked down in the late 1990s, and it appears that the only colony of this odd and ancient virus was lost with it. Since then, however, other colonies of even more

Such strange and foreign bioparticles, it has been argued, are evidence for the existence of a fourth domain of life, in addition to bacteria, archaea, and eukaryotes, the latter of which include complex life like us. Where microbes are concerned, we are really just at the beginning. III

1928, while Alexander Fleming was away on a holiday from his job as a medical researcher at St. Mary’s Hospital in London, some spores of mold from the genus Penicillium drifted into his lab and landed on a petri dish that he had left unattended. Thanks to a sequence of chance events—that Fleming hadn’t cleaned up his petri dishes before departing on holiday, that the weather was unusually cool that summer (and thus good for spores), that Fleming remained away long enough for the slow-growing mold to act—he returned to find that the bacterial growth in the petri dish had been conspicuously inhibited.

early 1941, they had just enough to trial the drug on a policeman named Albert Alexander, who was a tragically ideal demonstration of how vulnerable humans were to infections before antibiotics. While pruning roses in his garden, Alexander had scratched his face on a thorn. The scratch had grown infected and spread. Alexander had lost an eye and now was delirious and close to death.

Within two days, he was sitting up and looking almost back to normal. But supplies quickly ran short. In desperation the scientists filtered and reinjected all they could from Alexander’s urine, but after four days the supplies were exhausted. Poor Alexander relapsed and died. With Britain preoccupied by World War II and the United States not yet in it, the quest to

Then, two years after testing had begun, a lab assistant in Peoria named Mary Hunt brought in a cantaloupe from a local grocery store. It had a “pretty golden mold” growing on it, she recalled later. That mold proved to be two hundred times more potent

anything previously tested. The name and location of the store where Mary Hunt shopped are now forgotten, and the historic cantaloupe itself was not preserved: after the mold was scraped off, it was cut into pieces and eaten by the staff. But the mold lived on. Every bit of penicillin made since that day is descended from that single random cantaloupe. Within

As early as 1945, in his Nobel acceptance speech, Fleming warned that microbes could easily evolve resistance to antibiotics if they were carelessly used. Seldom has a Nobel speech been more prescient.

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. Sweden banned the agricultural use of antibiotics in 1986. The European Union followed in 1999. In 1977, the Food and Drug Administration ordered a halt to the use of antibiotics for purposes of fattening farm animals, but backed off when there was an outcry from agricultural interests and the congressional leaders who supported them. In 1945, the year that Alexander Fleming won the Nobel Prize, a typical case of pneumococcal pneumonia could be knocked out with forty thousand units of penicillin. Today, because of increased resistance, it can take more than twenty million units per day for many days to achieve the same result. On some diseases, penicillin now has no effe...

Staphylococcus aureus is a microbe found commonly on human skin and in nostrils. Generally it does no harm, but it is an opportunist, and when the immune system is weakened, it can slip in and wreak havoc. By the 1950s, it had evolved resistance to penicillin, but luckily another antibiotic called methicillin had become available and it stopped S. aureus infections in their tracks. But just two years after methicillin’s introduction, two people at the Royal Surrey County Hospital in Guildford, near London, developed S. aureus infections that would not respond to methicillin. S. aureus had, almost overnight, evolved a new drug-resistant form. The new strain was dubbed Methicillin-resistant Staphylococcus aureus, or MRSA. Within two years, it had

Today, MRSA and its cousins kill an estimated 700,000 people around the world annually. Until recently a drug called vancomycin was effective against MRSA, but now resistance has begun to emerge to it. At the same time, we are facing the formidable-sounding carbapenem-resistant Enterobacteriaceae (CRE) infections, which are immune to virtually everything we can throw at them. CRE kills about half of all those it sickens. Luckily, so far, it doesn’t usually infect healthy people. But watch out if it does. Yet as the problem has grown, the pharmaceutical

Pharmaceutical patents last only for twenty years, but that includes the period of clinical trials. Manufacturers usually have just five years of exclusive patent protection.” In consequence, all but two of the eighteen largest pharmaceutical companies in the world have given up the search for new antibiotics. People take antibiotics for only a week or two. Much better to focus on drugs like statins or antidepressants that people can take more or less indefinitely. “No sane company will develop the next antibiotic,” Kinch says. The problem needn’t be hopeless, but it does need to be addressed. At the current rate of spread, antimicrobial resistance is forecast to lead to ten million preventable deaths a year—that’s more people than die of

as a doctor put it to me, “We are looking at a possibility where we can’t do hip replacements or other routine procedures because the risk of infection is too high.” The day when people die once again from the scratch of a rose thorn may not be far away.

MOST EXTRAORDINARY thing in the universe is inside your head. You could travel through every inch of outer space and very possibly nowhere find anything as marvelous and complex and high functioning as the three pounds of spongy mass between your ears.

For an object of pure wonder, the human brain is extraordinarily unprepossessing. It is, for one thing, 75 to 80 percent water, with the rest split mostly between fat and protein. Pretty amazing that three such mundane substances can come together in a way that allows us thought and memory and vision and aesthetic appreciation and all the rest. If you were to lift your brain out of your skull, you would almost certainly be surprised at how soft it is. The consistency of the brain has been variously likened to tofu, soft butter, or a slightly overcooked Jell-O pudding. The great paradox of the brain is that everything you know about the world is provided to you by an organ that has itself never seen that world. The brain exists in silence and darkness, like a dungeoned

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 newborn infants, it’s no less than 65 percent. That’s partly why babies sleep all the time—their growing brains exhaust them—and have a lot of body fat, to use as an energy reserve when needed. Your muscles actually use even more

Unlike other parts of the body, the brain burns its four hundred calories at a steady rate no matter what you are doing. Hard thinking doesn’t help you slim. In fact, it doesn’t seem to confer any benefit at all. An academic at the University of California at Irvine named Richard Haier used positron emission tomography scanners to find that the hardest-working brains are usually the least productive. The most efficient brains, he found, were those that could solve a task quickly and then go into a kind of standby mode.

We use exactly the same components—neurons, axons, ganglia, and so on—as a dog or hamster. Whales and elephants have much larger brains than we have, though of course they also have much larger bodies. But even a mouse

The tiny space between nerve cell endings is called a synapse. Each neuron connects with thousands of other neurons, giving trillions and trillions of connections—as

What is surely most curious and extraordinary about our brain is how largely unnecessary it is. To survive on Earth, you don’t need to be able to write music or engage in philosophy—you really only need to be able to outthink a quadruped—so why have we invested so much energy and risk in producing mental capacity that we don’t really need? That is just one of the many things about your brain that your brain won’t tell you. —

is the home of our more basic operations: sleeping, breathing, keeping the heart going. The brain stem doesn’t get a lot of attention in the popular consciousness, but it is so central to our existence that “brain-stem death” is the fundamental measure of deadness in humans in the United Kingdom. Scattered through the brain rather like nuts in a fruitcake are many smaller structures—hypothalamus, amygdala, hippocampus, telencephalon, septum pellucidum, habenular commissure, entorhinal cortex, and a dozen or so others—which are collectively known as the limbic system (from the Latin limbus, meaning “peripheral”). It’s easy to go a lifetime without hearing a word about any of these components unless they go wrong. The basal ganglia, for instance, play an important part in movement, language, and

The most important component of the limbic system is a little powerhouse called the hypothalamus, which isn’t really a structure at all but just a bundle of neural cells.

hypothalamus is curiously unimposing. Though only about the size of a peanut and weighing barely a tenth of an ounce, it controls much of the most important chemistry of the body. It regulates sexual function, controls hunger and thirst, monitors blood sugar and salts, decides when you need to sleep. It may even play a part in how slowly or rapidly we age. A large measure of your success or failure as a human being is dependent on this tiny thing in the middle of your head.

hippocampus is central to the laying down of memories. (The name comes from

amygdala (Greek for “almond”) specializes in handling intense and stressful emotions—fear, anger, anxiety, phobias of all types. People whose amygdalae are destroyed are left literally fearless, and often cannot even recognize fear in others. The amygdala grows particularly lively when we are asleep, and thus may account for why our dreams are...

For each visual input, it takes a tiny but perceptible amount of time—about two hundred milliseconds, one-fifth of a second—for the information to travel along the optic nerves and into the brain to be processed and interpreted. One-fifth of a second is not a trivial span of time when a rapid response is required—to step back from an oncoming car, say, or to avoid a blow to the head. To help us deal better with this fractional lag, the brain does a truly extraordinary thing: it continuously forecasts what the world will be like a fifth of a second from now, and that is what it gives us as the present. That means that we never see the world as it is at this very instant, but rather as it will be a fraction of a moment in the future. We spend our whole lives, in other words, living in

Sound and light reach you at very different speeds—a phenomenon we experience every time we hear a plane passing overhead and look up to find the sound coming from one part of the sky and a plane moving silently through another. In the more immediate world around you, your brain normally irons out these differences, so that you sense all stimuli as reaching you simultaneously. In a similar way, the brain

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

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. Consider a bar of soap. Has it ever struck you that soap lather is always white no matter what color the soap is? That isn’t because the soap somehow changes color when it is moistened and rubbed. Molecularly, it’s exactly as it was before. It’s just that the foam reflects light in a different way. You get the same effect with

Although most of the growth of the brain occurs in the first two years and is 95 percent completed by the age of ten, the synapses aren’t fully wired until a young person is in his or her mid- to late twenties. That means that the teenage years effectively extend well into adulthood. In the meantime, the person in question will almost certainly have more impulsive, less reflective behavior than his elders and will also be more susceptible to the effects of alcohol. “The teenage brain is not just an adult brain with fewer miles on it,” Frances E. Jensen, a neurology professor, told Harvard Magazine in 2008. It is, rather, a different kind of brain altogether.

The nucleus accumbens, a region of the forebrain associated with pleasure, grows to its largest size in one’s teenage years. At the same time, the body produces more dopamine, the neurotransmitter that conveys pleasure, than it ever will again. That is why the sensations you feel as a teenager are more intense than at any other time of life. But it also means that seeking pleasure is an occupational hazard for teenagers. The leading cause of deaths among teenagers is accidents—and the leading cause of accidents is simply being with other teenagers. When more than one teenager is in a car, for instance, the risk of an accident multiplies by 400 percent. Everybody has heard of neurons, but not so many are familiar with the other main brain cells, glia or glial cells, which is a little odd because they outnumber neurons by ten to one. Glia (the word means “glue” or “putty”) are the cells that support neurons in the brain and central nervous system. For a long time,

About two-thirds of Freeman’s subjects received no benefit from the procedure or were worse off. Two percent died. His most notorious failure was Rosemary Kennedy, sister of the future president. In 1941, she was twenty-three years old, a vivacious and attractive girl but headstrong and with a tendency to mood swings. She also had some learning difficulties, though these seem not to have been nearly as severe and disabling as has sometimes been reported. Her father, exasperated by her willfulness, had her lobotomized by Freeman without consulting his wife. The lobotomy essentially destroyed Rosemary. She spent the next sixty-four years in care homes, incontinent, unable to speak, and bereft of

his book Into the Gray Zone, Owen discusses the case of a patient named Amy who suffered a serious head injury in a fall and for years lay in a hospital bed. Using an fMRI scanner, and carefully watching the woman’s neural responses when researchers asked her a series of questions, they were able to determine that she was fully conscious. “She had heard every conversation, recognised every visitor, and listened intently to every decision being made on her behalf.” But she was unable to move a muscle—to open her eyes, scratch an itch, express any desire. Owen believes that something in the region of 15 to 20 percent of people thought to be in a permanent vegetative state are in fact fully aware. Even now the only certain way to tell if a brain is working is if its owner says it is. Perhaps nothing is more unexpected about our brains than that they are much smaller today than they were ten thousand or twelve thousand years ago, and by quite a lot. The average brain has shrunk from 1,500 cubic centimeters then to 1,350 cubic centimeters now. That’s equivalent to scooping out a portion of brain about the size of a tennis ball. That’s not at all easy to explain, because it happened all over the world at the same time, as if we agreed to reduce our brains by treaty. The common presumption is that our brains have simply become more efficient and able to pack more performance into a smaller space, rather like cell phones, which have grown more sophisticated as they have contracted...

decapitated head will still have some oxygenated blood in it, so loss of consciousness may not be instantaneous. Estimates of how long the brain can keep working range from two seconds to seven, and that is assuming a clean removal, which was by no means always the case. Heads don’t come off easily even with stout blows from a specially sharpened ax wielded by an expert. As

Davis’s fundamental ambition was to prove that dark-skinned people were created separately from light-skinned people. He was convinced that a person’s intellect and moral compass were indelibly written in the curves and apertures of the skull and that these were exclusively products of race and class. People with “cephalic peculiarities” should be treated “not as criminals but as dangerous idiots,” he suggested. In 1878, at the age of seventy-seven, he married a woman fifty years his junior. What her cranium was like is unknown. This instinct on the part of European authorities to prove all other races inferior was widespread, if not universal. In England, in 1866 the eminent physician John Langdon Haydon Down (1828–96) first described the condition that we now know as Down’s syndrome in a paper called “Observations on an Ethnic Classification of Idiots,” but he referred to it as “Mongolism” and its victims as “Mongoloid idiots” in the belief that they were suffering an innate

speech center is still called Broca’s area, and the impediment Broca discovered is Broca’s aphasia. (Under it, a person can understand speech but can’t reply except to utter meaningless noises or sometimes stock phrases like “I’ll say” or “Oh, boy.”) Broca was less astute, however,

Ekman concluded that six expressions are universal: fear, anger, surprise, pleasure, disgust, and sorrow. The most universal expression of all is a smile, which is rather a nice thought. No society has ever been found that doesn’t respond to smiles in the same way. True smiles are brief—between two-thirds of a second and four seconds. That’s why a held smile begins to look menacing. A true smile is the one expression that we cannot fake. As the French anatomist G.-B. Duchenne de Boulogne noticed as long ago as 1862, a genuine, spontaneous smile involves the contraction of the orbicularis oculi muscle in each eye, and we have no independent control over those muscles. You can make your mouth smile, but you can’t make your eyes sparkle with feigned joy.

Nearly all of us miss these telltale expressions, according to Ekman, but we can be taught to spot them, assuming we want to know what workmates and loved ones really think of us.*2

the many species of hominids that preceded us had prominent browridges, but we Homo sapiens gave them up in favor of our small, active eyebrows. It’s not easy to say why. One theory is that eyebrows are there to keep sweat out of the eyes, but what the eyebrows do really well is convey feelings. Think how many messages you can send with a single arched eyebrow, from “I find that hard to believe” to “Watch your step” to “Care to have sex?” One of the reasons the Mona Lisa looks enigmatic is that she has no eyebrows. In

known people: one with the eyebrows eliminated and the other with the eyes themselves taken away. Surprisingly, but overwhelmingly, volunteers found it harder to identify the celebrities without eyebrows than without eyes. Eyelashes are similarly uncertain. There is

Most mysterious of all is the chin. The chin is unique to humans, and no one knows why we have one. It doesn’t seem to confer any structural benefit to the head, so it may be simply that we find a good chin dashing. Lieberman, in a rare moment of lightness, observed, “Testing this last hypothesis is especially difficult, but the reader is encouraged to think of appropriate experiments.” It is certainly the case that we talk about “chinless wonders” and otherwise equate modest chins with deficiencies of character and intellect. —

curious that we always speak of our five senses because we have way more than that. We have a sense of balance, of acceleration and deceleration, of where we are in space (what is known as proprioception), of time passing, of appetite. Altogether (and depending on how you count them) we have as many as thirty-three systems within us that let us know where we are and how we are doing.

The rods and cones that detect light are at the rear, but the blood vessels that keep it oxygenated are in front of them. There are vessels and nerve fibers and other incidental detritus all over, and your eye has to see through all this. Normally, your brain edits out any interference, but it doesn’t always succeed. You might have had the experience of looking at a clear blue sky on a sunny day and seeing little white sparks popping in and out of existence, like the briefest of shooting stars. What you are seeing, amazingly enough, is your own white blood cells, moving through a capillary in front of the retina. Because white blood cells are big (compared with

technical name for these disturbances is Scheerer’s blue field entoptic phenomena (named for a German ophthalmologist of the early twentieth century, Richard Scheerer), though they are more commonly and poetically known as blue sky sprites. They are especially visible against a bright blue sky simply because of the way the eye absorbs different wavelengths

Floaters are a similar phenomenon. They are clumps of microscopic fibers in the jellylike vitreous humor of your eye, which cast a shadow on the retina. Floaters are a common occurrence as you get older, and are generally harmless, though they can indicate a retinal tear. The technical name for them, if you wish to impress someone, is muscae volitantes, or “hovering flies.” If you held a human eyeball in your hand, you might

The front part—the lens and cornea—captures passing images and projects them onto the back wall of the eye—the retina—where photoreceptors convert them into electrical signals that are passed on to the brain via the optic nerve.

on closer examination, as with almost every part of the body, it is a wonder of complexity. It has five layers—epithelium, Bowman’s membrane, stroma, Descemet’s membrane, and endothelium—laminated into a space just slightly over half a millimeter thick. In order to be transparent, it has a very modest blood supply—indeed, practically none. The part of the eye that has the most photoreceptors—that really does

Tears come in three varieties: basal, reflex, and emotional. Basal are the functional ones that provide lubrication. Reflex tears are those that emerge when the eye is irritated by smoke or sliced onions or similar. And emotional tears are of course self-evident, but they are also unique. We are the only creatures that cry from feeling, as far as we can tell. Why we do so is another of life’s many mysteries. We get no physiological benefit from erupting in tears. It is also a little odd surely that this act signifying powerful sadness