The Body: A Guide for Occupants

by Bill Bryson

According to Jeffrey Linder, professor of medicine at Harvard, antibiotics are prescribed for 70 per cent of acute bronchitis cases even though guidelines explicitly state that they are of no use there.

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 one-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 a world that doesn’t quite exist yet.

Many observers at executions claimed to have witnessed evidence of consciousness from newly separated heads. Charlotte Corday, guillotined in 1793 for the murder of the radical leader Jean-Paul Marat, was said to wear a look of fury and resentment when the executioner held her head up to the cheering crowd.

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 is also triggered by extreme joy or quiet rapture or intense pride or almost any other potent emotional state.

The iris is what gives the eye its colour. It is composed of a pair of muscles that adjust the opening of the pupil, rather like the aperture on a camera, to let in or keep out light as needed. Superficially, the iris looks like a neat ring, encircling the pupil, but closer inspection shows that it is in fact ‘a riot of spots, wedges, and spokes’, in the words of Daniel McNeill, and these patterns are unique to each of us, which is why iris recognition devices are now increasingly used to identify us at security checkpoints.

It is known as the Valsalva effect and it arises because the air pressure inside your head fails to keep up with the changing air pressure outside it. Making your ears pop by blowing out while keeping your mouth and nose closed is known as the Valsalva manoeuvre. Both are named for a seventeenth-century Italian anatomist, Antonio Maria Valsalva,

A heart attack and a cardiac arrest, though usually confused by most of us, are in fact two different things.12 A heart attack occurs when oxygenated blood can’t get to heart muscle because of a blockage in a coronary artery. Heart attacks are often sudden – that’s why they are called attacks – whereas other forms of heart failure often (though not always) are more gradual. When heart muscle downstream of a blockage is deprived of oxygen, it begins to die, usually within about sixty minutes. Any heart muscle we lose in this way is gone for ever, which is a bit galling when you consider that other creatures much simpler than we are – zebrafish, for instance – can regrow damaged heart tissue. Why evolution deprived us of this useful facility is yet another of the body’s many imponderables.

Leptin’s effects turned out to be nothing like as straightforward as hoped. Today, nearly a quarter of a century after its discovery, we still haven’t figured out exactly how leptin works and are nowhere near being able to use it as an aid for weight control.

Henry Gray was a rising young demonstrator of anatomy at St George’s Hospital at Hyde Park Corner in London (the building still stands but is now a luxury hotel) when he decided to produce a definitive and modern anatomical guide. Gray was still only in his twenties when he began work on the book in 1855. For the illustrations he commissioned a medical student at St George’s named Henry Vandyke Carter for a payment of £150 spread over fifteen months. Carter was painfully shy, but highly gifted. All of his illustrations had to be drawn in reverse so that they would print the right way around on paper, which must have been an almost unimaginable challenge.6 Carter not only did all 363 drawings, but also nearly all the dissecting and other preparatory work. Although many other anatomy books were available, Gray’s, in the words of one biographer, ‘eclipsed all others, partly for its meticulous detail, partly for its emphasis on surgical anatomy, but most of all perhaps for the excellence of the illustrations’.

Tendons are strong, and generally it takes a lot of force to tear them, but they also have very little blood supply and therefore take a long time to heal. That at least is better than cartilage, which has no blood supply at all and therefore almost no capacity to heal.

The young and gracile proto-human famously known as Lucy, who lived in what is now Ethiopia some 3.2 million years ago and is often used as a model for early bipedalism, was only about three and a half feet tall and weighed just twenty-seven kilos – hardly the sort of presence to intimidate a lion or cheetah.

How do you know this?

‘He discovered that if a mouse was exposed to skin from another mouse when it was very young, then when the mouse grew up it would be able to accept a skin transplant from that second mouse. In other words, he discovered that at a young age the body learns what is self – what not to attack. You can get a skin transplant from one mouse to another as long as the recipient mouse has been trained in early life not to react to it.’ This was the insight that would, years later, win Medawar a Nobel Prize. As David Bainbridge has noted: ‘Although we take it for granted today, this sudden joining of transplantation and the immune system was a crucial point in medical science. It told us what immunity actually is.’ II

– if there is one thing your immune system knows, it is that you shouldn’t have a pig’s liver inside you – and the second is that pigs are full of something called porcine endogenous retroviruses (or PERVs for short), which could infect any humans into which they are introduced.

The formal name for the act of sneezing, by the way, is sternutation, though some authorities in their lighter moments refer to a sneeze as an autosomal dominant compelling helio-ophthalmic outburst, which makes the acronym ACHOO (sort of).

Interestingly, the discomfort you feel when you hold your breath for too long is caused not by the depletion of oxygen but by a build-up of carbon dioxide. That’s why the first thing you do when you stop holding your breath is blow out. You would think that the most urgent need would be to get fresh air in rather than stale air out, but no. The body so abhors CO2 that you must expel it before gulping in replenishment.

Drinking too much water can actually be dangerous.20 Normally your body manages fluid balance very well, but occasionally people take in so much water that the kidneys cannot get rid of it fast enough and they end up dangerously diluting the sodium levels in their blood, setting off a condition known as hyponatraemia.

but the muscles that control bodily movement are all restrained. The explanation most often proposed is that immobilization stops us from harming ourselves by thrashing about or trying to flee from attack when caught up in a bad dream. A very few people suffer from a condition called REM sleep behaviour disorder in which the limbs don’t become paralysed, and they do indeed sometimes hurt themselves or their partners with their thrashing. For others, paralysis doesn’t immediately abate upon awaking and the victim finds himself awake but unable to move – a deeply unnerving experience, it seems, but one that mercifully tends to last only for a few moments.

One of the most severe and challenging of all pains is said to be phantom limb pain, when the sufferer perceives agonies in a part of the body that has been lost to accident or amputation. It is an obvious irony that one of the greatest pains we feel can be in a part of us that is no longer there. Worse, unlike normal pain, which usually abates as a wound heals, phantom pain may go on for a lifetime. No one can yet explain why. One theory is that in the absence of receiving any signal from the nerve fibres in the missing body part, the brain interprets this as an injury so severe that the cells have died, and so sends out an unending call of distress, like a burglar alarm that won’t turn off. If surgeons know they are going to amputate a limb, they now often numb the nerves in the affected limb over a period of days beforehand to prepare the brain for the oncoming loss of feeling. The practice has been found to greatly reduce phantom limb pain.

A successful virus is one that doesn’t kill too well and can circulate widely.11 That’s what makes flu such a perennial threat.