Why it’s a MIRACLE that you don’t choke to death every time you eat!

deaths of people who had supposedly died of heart attacks in restaurants and, without much difficulty, found nine who had in fact choked.

But even using the most cautious estimates, choking is the fourth most common cause of accidental death in America today.

The greatest choking authority of all time was almost certainly a dour American doctor with the luxuriant name of Chevalier Quixote Jackson, who lived from 1865 to 1958. Jackson has been called ‘the father of American broncho-esophagoscopy’.

His obsession was with foreign objects that had been swallowed or inhaled. Over a career that lasted almost 75 years, Jackson specialised in designing instruments and refining methods for retrieving such objects – and built up an extraordinary collection of 2,374 imprudently ingested items.

Today, the Chevalier Jackson Foreign Body Collection is housed in a cabinet in the basement of the Mutter Museum of the College of Physicians of Philadelphia. Among the objects Jackson retrieved from the gullets of the living or dead were a wristwatch, a crucifix with rosary beads, miniature binoculars, a small padlock, a toy trumpet, a fullsized meat skewer, a radiator key, several spoons, a poker chip, and a medallion that said (perhaps just a touch ironically) ‘Carry Me For Good Luck’. OUR PAINKILLER MORE POTENT THAN MORPHINE IT WILL not have escaped your attention that the mouth is a moist and glistening vault. That’s because 12 salivary glands are distributed around it. A typical adult secretes about two-and-a-half pints (or a little less than 1.5 litres) of saliva a day. According to one calculation, we secrete some 30,000 litres in a lifetime (as much as in 200 deep baths). Saliva is almost entirely water. Only 0.5 per cent of it is anything else, but that tiny portion is full of useful enzymes – proteins that speed up chemical reactions. Among these are amylase and ptyalin, which begin to break down sugars in carbohydrates while they are still in our mouths. Chew a starchy food like bread or potato for a bit longer than normal and you will soon notice a sweetness. Unfortunately for us, bacteria in our mouths like that sweetness too; they devour the liberated sugars and excrete acids, which drill through our teeth and give us cavities.

Other enzymes, notably lysozyme – discovered by Alexander Fleming before he stumbled on penicillin – attack invading pathogens, but not the ones that cause tooth decay, alas. We are in the rather strange position that we not only fail to kill the bacteria that give us a lot of trouble, but actively nurture them.

Recently it was discovered that saliva also contains a powerful painkiller called opiorphin. It is six times more potent than morphine, though we have it only in very small doses, which is why you are not perennially high or indeed notably pain-free when you bite your cheek or burn your tongue. Because it is so dilute, no one is sure why it is there at all. It is so unassertive that its existence wasn’t even noticed until 2006.

We produce little saliva while we sleep, which is why microbes can proliferate then and give you a foul mouth to wake to. It is also why brushing your teeth at bedtime is a good idea – it reduces the number of bacteria you go to sleep with.

If you’ve ever wondered why no one wants to kiss you first thing in the morning, it is possibly because your exhalations may contain up to 150 different chemical compounds, not all of them as fresh and minty as we might hope.

Among the common chemicals that help to create morning mouth are methyl mercaptan (which smells very like old cabbage), hydrogen sulphide (like rotten eggs), dimethyl sulphide (slimy seaweed), dimethylamine and trimethylamine (rank fish), and cadaverine (yes, decaying bodies).

In the 1920s, Professor Joseph Appleton, of the University of Pennsylvania School of Dental Medicine, was the first to study bacterial colonies within the mouth and discovered that, microbially speaking, your tongue, teeth and gums are like separate continents, each with its own colonies of micro-organisms.

There are even differences in the bacterial colonies that inhabit the exposed parts of a tooth and those beneath the gum line. About 1,000 species of bacteria have been found in human mouths, although – and this is the good news – at any one time you are unlikely to have more than 200.

The mouth is not only a welcoming home for germs but an excellent way station for those that want to move elsewhere.

Paul Dawson, a professor of food science at Clemson University in South Carolina, has made something of a career of studying the ways people spread bacteria from themselves to other surfaces, such as when they share a water bottle or engage in ‘double dipping’ with crisps and salsa.

In a study called Bacterial Transfer Associated With Blowing Out Candles On A Birthday Cake, Dawson’s team found that candle-blowing across a cake increased the coverage of bacteria on it by up to 1,400 per cent, which sounds pretty horrifying but is in fact probably not much worse than the kinds of exposures we encounter in daily life anyway. THE MARVEL OF OUR ‘READY-MADE FOSSILS’ THE most familiar components of the mouth are of course the teeth and the tongue. Our teeth are formi

dable creations and nicely versatile, too. They come in three varieties: blades (which are pointy), cusps (which are spade-like) and basins, or fossae (which fall somewhere between the other two).

The outside of your tooth is the enamel. It is the hardest substance in the human body but forms just a thin layer and can’t be replaced if it is damaged. That’s why you have to go to the dentist for cavities.

Under the enamel is a much thicker layer of another mineralised tissue, called dentine, which can renew itself. At the centre of it all is the fleshy pulp containing nerves and blood supply.

Because they are so hard, teeth have been called ‘ready-made fossils’. When all the rest of you has turned to dust or dissolved away, the last physical trace of your existence on Earth may be a fossilised molar. We can bite pretty hard. Bite force is measured in units called newtons (in honour of Isaac), and if you are a typical adult male you can muster about 400 newtons of force, which is quite a lot, though nothing like as much as an orangutan, which can bite with five times as much vigour. Still, when you consider how well you can demolish, say, an ice cube (try doing that with your fist) and how little space the five muscles of the jaw occupy, you can appreciate that human chomping is pretty capable.

The tongue is a muscle, but quite unlike any other. For one thing it is exquisitely sensitive – think how adroitly you pick out something in your food that shouldn’t be there, like a tiny piece of eggshell or grain of sand – and intimately involved in vital activities like speech articulation and tasting food. When you eat, the tongue darts about like a nervous host at a cocktail party, checking the taste and shape of every morsel in preparation for dispatching it onwards to the gullet.

As everyone knows, the tongue is coated with taste buds. These are clumps of taste receptor cells found in the bumps on your tongue which are called papillae. They come in three different shapes – circumvallate (or rounded), fungiform (mushroom-shaped) and foliate (leaf-shaped). They are among the most regenerative of all cells and are replaced every ten days.

For years, even textbooks spoke of a tongue map, with the elemental tastes occupying a well-defined zone: sweet on the tip of the tongue, sour at the sides, bitter at the back.

In fact, that is a myth, traced to a textbook of 1942 by one Edwin G. Boring, a Harvard psychologist who misinterpreted a paper written by a German researcher 40 years before that.

Altogether, we have about 10,000 taste buds, mostly distributed around the tongue, except in the very middle where there are none. Additional taste buds are found in the roof of the mouth and lower down the throat, which is said to be why some medicines taste bitter as they go down. As well as those in the mouth, the body has taste receptors in the gut and throat, but they don’t connect to the brain in the same way as the taste receptors on your tongue, and for good reason. You don’t want to taste what your stomach is tasting.

Taste receptors have also been found in the heart, lungs and even the testicles. No one knows quite what they are doing there. It is generally supposed that they evolved for two deeply practical purposes: to help us find energy-rich foods (like sweet, ripe fruits) and to avoid dangerous ones. But they don’t always fulfil either role terribly well.

Captain James Cook, the great British explorer, had a salutary demonstration of that in 1774, on his second epic voyage through the Pacific. One of his crew caught a meaty fish, which no one aboard recognised. It was cooked and presented to the captain and two of his officers, but as they had already dined they merely sampled it and had the remainder put aside for the following day.

This was a very lucky thing, for in the middle of the night all three found themselves ‘seized with an extraordinary weakness and numbness all over our limbs’.

Cook was for some hours paralysed and unable to lift anything – even a pencil. The men were lucky to survive, for what they had sampled was puffer fish. These contain a poison called tetrodotoxin, which is 1,000 times more powerful than cyanide.

We have about 10,000 taste receptors, but our mouths have a greater number of receptors for pain and other sensations. Because these receptors exist side by side on the tongue, we sometimes mix them up. When you describe a chilli as hot, you are being more literal than you might suppose. Your brain interprets it as actually being burned. As Joshua Tewksbury, of the University of Colorado, has put it: ‘Chillis innervate the same neurons that you activate when you touch a 335F ring on your cooker. Essentially, our brain is telling us that we have got our tongue on the stove.’ In the same way, menthol is perceived as being cool even in the heated smoke of a cigarette.

As far as taste goes, our tongue can only identify the familiar basics of sweet, salty, sour, bitter and umami (a Japanese word meaning ‘savoury’ or ‘meaty’). Some authorities believe we also have taste receptors specifically allocated for metal, water, fat and another Japanese concept called kokumi, meaning ‘full-bodied’, but the only ones that are universally accepted are the five basics.

The tongue and its taste buds give us just the basic textures and attributes of foods – whether they are soft or smooth, sweet or bitter, and so on – but the full sensuousness of it all is dependent on our other senses. It is nearly always wrong to talk about how food tastes, though of course we all do. What we appreciate when we eat is flavour, which is taste plus smell.

Smell is said to account for at least 70 per cent of flavour and maybe even as much as 90 per cent. We appreciate this intuitively: if someone hands you a pot of yogurt and says ‘Is this strawberry?’ your response will be to sniff it, not taste it. That is because strawberry is actually a smell, perceived nasally, not a taste in the mouth.

When you eat, most of the aroma reaches you not through your nostrils but by the back staircase of your nasal passage, what is known as the retronasal route – as opposed to the orthonasal route up your nose. An

It takes a hundred different muscles... just to stand up

easy way to experience the limitations of your taste buds is to close your eyes, pinch shut your nostrils and eat a flavoured jelly bean collected blindly from a bowl. You will instantly apprehend its sweetness, but you almost certainly won’t be able to identify its flavour. But open your eyes and nostrils and its fruity specificity becomes immediately and redolently apparent.

Even sound materially influences how delicious we find food. People who are played a range of crunching sounds through headphones while sampling crisps from various bowls will always rate the noisier crisps as fresher and tastier even though all the crisps are the same.

Many tests demonstrate how easily we are fooled with respect to flavour. In a blind taste test at the University of Bordeaux, students in the Faculty of Oenology were given two glasses of wine, one red and one white. The wines were actually identical except that one had been made a rich red colour with an odourless and flavourless additive. The students without exception listed entirely different qualities for the two wines.

That wasn’t because they were inexperienced or naive. It was because their sight led them to have completely different expectations, and this powerfully influenced what they sensed when they took a sip from either glass. Odours and flavours are created entirely inside our heads. Think of something delicious – a moist, gooey, warm chocolate brownie fresh from the oven, say. Take a bite and savour the velvety smoothness, the rich, heady waft of chocolate that fills your head. Now consider the fact that none of those flavours or aromas actually exists. All that is going in your mouth is texture and chemicals. It is your brain that reads these scentless, flavourless molecules and enlivens them for your pleasure.

Your brownie is sheet music. It is your brain that makes it a symphony. As with so much else, you experience the world that your brain allows you to experience. SPEAKING... THE GREAT WONDER OF THE WORLD THERE is one other remarkable thing we do with our mouths and throats, and that is make meaningful noises. The ability to create and share complex sounds is one of the great wonders of human existence, and the characteristic more than any other that sets us apart from all other creatures that ever lived.

Speech and its development ‘are perhaps more extensively debated than any other topic in human evolution’, in the words of Harvard paleoanthropologist Daniel Lieberman. No one knows even approximately when speech began on Earth and whether it is an accomplishment confined to homo sapiens or whether it was mastered by archaic humans like Neanderthals and homo erectus.

What is certain is that the capacity for speech requires a delicate and co-ordinated balance of tiny muscles, ligaments, bones, and cartilage of exactly the right length, tautness and positioning in order to expel microbursts of modulated air in just the right measures. The tongue, teeth and lips must also be nimble enough to take these throaty breezes and turn them into nuanced phonemes. And all of this must be achieved without compromising our ability to swallow or breathe. It isn’t just a big brain that allows us to speak, but an exquisite arrangement of anatomy. One reason chimpanzees can’t talk is that they appear to lack the ability to make subtle shapes with tongue and lips to form complex sounds.

It may be that all this happened fortuitously in the course of an evolutionary redesign of our upper bodies to accommodate our new posture when we became bipedal. Or it may be that some of these features appeared through the slow, incremental wisdom of evolution. But the bottom line is that we ended up with brains big enough to handle complex thoughts and vocal tracts uniquely able to articulate them.

The larynx is essentially a box about an inch to an inch-and-ahalf on each side. Within and around it are nine cartilages, six muscles and a suite of ligaments, including two known as the vocal cords but more properly known as the vocal folds. When air is forced through them, the vocal folds snap and flutter (like flags in a stiff breeze, it has been said), producing a variety of sounds, which are refined by tongue, teeth and lips working together into the wondrous, resonant, informative exhalations known as speech. The three phases of the process are respiration, phonation and articulation. Respiration is simply the pushing of air past the vocal ligaments; phonation is the process of turning that air into sound; and articulation is the refinement of sound into speech.

If you wish to appreciate what a marvel speech is, try singing a song – Frere Jacques serves very well – and notice how effortlessly melodic the human voice is. Your throat is a musical instrument as well as a sluice and wind tunnel. We should also take a moment to consider the strange little fleshy appendage that stands guard where all becomes darkness. I refer to the mysterious uvula. (The name comes from the Latin for ‘little grape’, even though it is not especially like a grape at all.)

For a long time, nobody knew what it was for. We are still not completely sure, but it seems to be a mudflap for the mouth. It directs food down the throat and away from the nasal passage. It also helps with the production of saliva and may also play a part in speech. People who have had their uvula removed lose some control over guttural sounds.

The rattling of the uvula in sleep appears to be a significant component of snoring, and is often the reason uvulas are taken out. The uvula, in short, is a curious thing. Considering its position at the very centre of our largest orifice, at the point of no return, it seems oddly inconsequential. There is perhaps a kind of strange double comfort in knowing that you will almost certainly never lose your uvula, but that it wouldn’t matter too much anyway if you did.

Humans can make at least 4,000 different facial expressions

Abridged extract from The Body: A Guide For Occupants, by Bill Bryson, published by Doubleday on October 3 at £25. Offer price £18.75 (20 per cent discount) until September 30. To pre-order, call 01603 648155 or go to mailshop.co.uk. See Bill Bryson live on stage in a new theatre show. For information and tickets, go to lateralevents.com.