73 pages • 2 hours read
Bill BrysonThe Body: A Guide for Occupants
Nonfiction | Book | Adult | Published in 2019A modern alternative to SparkNotes and CliffsNotes, SuperSummary offers high-quality Study Guides with detailed chapter summaries and analysis of major themes, characters, and more.
Chapters 1-3 Chapter Summaries & Analyses
Chapter 1 Summary: “How to Build a Human”
How much it would cost in materials to build a human body: Sixty-one percent of the body is oxygen and 10% is hydrogen—these, along with nitrogen, are inexpensive. Purified carbon, however, would cost nearly $70,000, and calcium, phosphorus, and potassium together would cost $73,800. The remaining 1% of body weight is made of trace amounts of thorium, molybdenum, vanadium, copper, and a few dozen other elements. The total cost to construct, for example, actor Benedict Cumberbatch—not counting labor and tax—is $151,578.46.
Humans don’t yet know how to build a simple cell, much less an entire body: “The only thing special about the elements that make you is that they make you. That is the miracle of life” (4). The human body contains “7 billion billion billion” atoms (5). In the time it takes to read a short sentence, the body manufactures 1 million red blood cells. Stretched out thinly, the lungs would cover a tennis court. All the DNA in the all the cells of the body, lined up, would reach billions of miles beyond Pluto.
The body is built from genetic instructions contained in the microscopic strands of DNA at the center of cells, instructions that describe how to build the proteins that make up the body. The ultimate purpose of DNA is to produce more DNA; each living being descends from previous beings constructed by DNA in an unbroken chain 3 billion years long. Of the 8,000 ways to die compiled by the World Health Organization, every person avoids all but one.
Chapter 2 Summary: “The Outside: Skin and Hair”
At 20 square feet and 15 to 20 pounds, the skin, or cutaneous system, is the body’s largest organ; “it keeps our insides in and bad things out” (11). The surface, or epidermis, is made of dead skin cells that flake off into dust, about a pound per year. Beneath that is the dermis, the living skin, with blood vessels, a superb sensory system, 2 to 5 million hair follicles with sebaceous glands that secrete skin oil, and up to 10 million sweat glands. Under the skin is a subcutaneous layer of insulating fat.
Skin is colored by melanin, a chemical common in nature; it pigments feathers, squid ink, browning fruits, and hair. An excellent sunblock, melanin production has evolved many times in separate groups of humans, leading to a wide variety of shades adapted to local sunlight conditions. As people migrated northward, their sink depigmented over the generations, but many people today still don’t get enough Vitamin D from sunlight on their skin or from food.
People have millions of hair follicles, as much hair as other mammals, but it’s wispier, with none on palms, soles, lips or genitalia. Head hair is a good insulator and sun reflector. Mammals get goose bumps when cold or angry, causing fur to rise up and create an insulating layer of warm air, but thin human hair serves little purpose. Hair follicles have growth cycles and then rest, the hair falling out. Leg hairs last about two months, while scalp hair can last seven years.
Around 1900, Alphonse Bertillon developed a system for catching repeat criminals. He measured 11 body parts on suspects, including cheek width, left pinkie length, and height when sitting, that wouldn’t change with age. Bertillon also took the first mug shots and fingerprints. His system caught 241 crooks in the initial year, and a fingerprint was used to catch a murderer in 1902. “Bertillonage” took crime prevention by storm.
Scientists believe fingerprints help hands grip better and increase finger sensitivity, but they’re not sure why people sweat. Humans are far less hairy than other mammals yet have more sweat glands, which permits better skin cooling and allows the human brain to be very large without overheating. The average man contains 42 quarts of water and will sweat or respire or urinate about 1.5 quarts per day unless he exerts himself, which will cost him up to 1.5 quarts per hour—easily a dozen quarts from walking all day in the hot sun, which can be fatal.
Sweat is 99.5% water; the rest is salt and other chemicals. Dehydrated people must replace the salt as well as the water. Sweat is odorless but becomes smelly after bacteria digest it. Skin harbors about 200 types of bacteria, but they vary due to several factors, including what fabrics are worn and when a person bathes. Skin germs are hard to remove: They require a full minute of hand washing after every medical examination, which is why hospitals have a hard time preventing transmission of infections.
Itching often has no known cause. Some people who have had a limb amputated suffer a maddening itch from the missing extremity. Equally frustrating can be hair loss: Most men become bald by age 50, while their nose and ear hairs can grow profusely. The only known cure, understandably unpopular, is castration.
Chapter 3 Summary: “Microbial You”
Without microbes, humans wouldn’t survive. Many foods would fail to grow without them. Trillions of microscopically tiny bugs live in the human gut, helping to digest food and increasing nutrient availability by 10%. Humans are made of 35 trillion cells but they also harbor roughly as many microbes, with 40,000 different varieties of bacteria, archaea, protists, viruses, and fungi in and on the average human.
Bacteria reproduce up to 70 times a day. They mutate easily and exchange DNA, making them highly adaptable. More than 95% of the mass of life on Earth is microbial.
Viruses are assemblages of proteins much smaller even than bacteria. They are everywhere—100 billion in a quart of seawater, for example—but quite inert unless swept up into a body, where they awaken and reproduce rapidly. Of hundreds of thousands of virus species, only 263 infect humans; more than 100 can cause the common cold. Viruses spread rapidly, from an office doorknob to all the shared equipment and half the personnel within four hours.
Fungi, like molds and yeasts, exist in several million species, but only about 300 affect humans, usually in minor ways such as athlete’s foot but sometimes more seriously, as with thrush and valley fever. About a million humans die each year from fungal infections.
Microbes that don’t fit easily into the other main groups are called protists. This is “a huge category and includes amoebas, paramecia, diatoms, slime molds, and many others” (36). The most well-known disease caused by a protist is malaria.
The first truly effective cure for microbial illnesses—penicillin, made from mold—was developed late in World War II. Penicillin and other antibiotics have since been overused, mostly to fatten farm animals, and germs have evolved resistance to the medicines. Pharmaceutical companies shy away from developing new drugs because the process has become so expensive. Today’s death rate from microbial infection is the same as it was in 1980; the rate may someday fall back to the deadly times before penicillin.
Chapters 1-3 Analysis
The first three chapters provide an overview of the body, how it interacts with the outside world via the skin, and how the outside world colonizes it with microbes.
Chapter 1 presents the human body as a miracle of self-replicating complexity, an elaborate organic machine whose complex functioning serves one overriding purpose: to reproduce its genetic material in offspring that, in turn, follow the same imperative. People alive today contain an unbroken chain of DNA that stretches back billions of years, a form of immortality almost beyond comprehension. Together with the sheer number of cells that make up the organism, alongside the immense complexity of ordinary day-to-day physical functioning, these numbers beggar the imagination.
As for the skin, it is so complex and individualized that its oddities and unique features and symptoms are fascinatingly, and sometimes dismayingly, large. As far as is known, no two people have the same fingerprints or the exact same skin type. Pigmentation varies as a spectrum, each tint more or less adapted to the region in which the owner of the skin resides. Dark implies a lot of sun exposure while pale pink suggests northern or cloudy environments.
With the high mobility of modern life, inherited skin pigmentation often doesn’t suit the physical environments in which people live. Dark-skinned people must worry about getting enough Vitamin D in northern climes while light-skinned residents of the tropics need plenty of sunblock to prevent sunburn and skin cancer.
Throughout history, skin color has been a signal of tribal affiliation and sometimes of social status. Humans often make skin tint a mark of superiority or inferiority. Though it can reveal quite a bit about the physical condition of the body inside it, skin reveals virtually nothing about a person’s character or intelligence. People have tried to assert that skin color itself indicates brainpower, or goodness, or some other trait, when such variables are unrelated to the body’s need simply to protect itself from, or avail itself of, the banes and benefits of sunlight.
Urban life encourages people to live and work with others whose skin color would once have kept them apart. Today’s world offers the subversive possibility that the old racial stereotypes, along with the various skin colors, may begin to melt away in a future of mixed families. The possibilities are unpredictable.
Chapter 3 mentions the overuse of antibiotics. Patients sometimes go to the doctor with a cold or flu and insist on getting a course of antibiotics, but these illnesses are caused by viruses and can’t be cured with antibiotics. Doctors know this, but their patients are paying the bills, and sometimes the physicians cave, hoping the prescriptions won’t contribute too much to the growing microbial immunity to antibiotics.
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