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Adventures on the Alimentary Canal

Mary Roach

I don't want you to say, "This is gross," I want you to say, "I thought this would be gross, but it's really interesting." Okay, and maybe a little gross.

The microwave meals we buy have virtually flavorless meat. The flavor comes entirely from the sauce. They have a common base to which they add 2 or 3 different sauces to have a full product line.

Pet foods come in a variety of flavors because that's what we like and we assume animals do to. But that's wrong. Cats in particular stick to one thing all the time.In the wild, they are either birders or mousers. The human bias sometimes becomes absurd. Although cats are 100% carnivore, and their natural diet contains no plants, there is a big market for vegetarian cat food because that's what the owners want.

Cats, unlike omnivores, cannot taste sweetness. There's no need, because their natural diet has no carbohydrates, which is where we get our simple sugars. Rats, on the other hand, are slaves to sweetness. They have been known to die of malnutrition rather than step away from a sugar-water drip.

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Cancer patients whose taste receptors have been destroyed by radiation treatments, find it very difficult to eat. "Your body is saying, 'It's not food, it's cardboard', and it won't let you swallow." These people actually starve to death.

You can advertise condoms and even vibrators in mainstream magazines now, but not pills that take away (sulfur part of) small of farts.

'Morning breath' is hydrogen sulfide released by the bacteria consuming shed tongue cells while you mouth-breathe for eight hours: saliva normally washes the debris away.

Molecule for molecule, hydrogen sulfide is as lethal as cyanide, which is probably why we have evolved such a sensitivity to it. The concentration in a fart is between 1 and 3 parts per million. Harmless. But at a 1000 parts per million - which you can get in pig manure pits and septic tanks - it causes respiratory paralysis and suffocation. The problem is that as soon as the concentration goes over 150 parts per million, your olfactory nerves are overwhelmed and paralyzed, and you no longer detect the warning smell. So co-workers or family rush into the manure pit to rescue the fallen, in a chain of death.

(London Times)

Our gastrointestinal tracts are horribly neglected. Even as we obsess publicly about what we cook and eat, observes science journalist Mary Roach, how we eat and digest remains a matter of embarrassed ignorance. Feeding, and its 'unsavoury correlates', she argues, are as taboo as mating and dying. Why else would anal cancer be seemingly the last to acquire its own charity (in 2010) and its distinctively amber-coloured ribbon?

To Roach, of course, any taboo is a delicious opportunity. She has written funnily and intrepidly on the science of mating (Bonk), being dead (Stiff) and living in space (Packing for Mars). Her gleeful but well-researched books bubble with irresistible did-you-knows. Gulp, however, presents a challenge. A salty dinner party might just enjoy talk of freeze-dry burial or pig insemination. It balks, however, at discussion of why we won't drink our own saliva, whether men's or women's farts are smellier or how Elvis Presley really died. (I know: I tried out all three topics.)

Yet these questions are more than opportunities to shock. The saliva issue, for instance, helps define where we draw the limits of our sense of self. Fascinatingly, most of us are comfortable with our own spit until the point when it has left the tip of our extended tongue, though conservative Brahmins regard even spittle on their own lips as defiling. Equally fascinating, many people extend the boundary to include their children (many are not disgusted by their own infants' nappies) and their lovers (they may even ingest bodily fluids). This is presumably why french kissing is so intimate: it's a way of signalling oneness.

Roach's three whole chapters on farting, meanwhile, are more than merely diverting. Men have higher volumes, if you must know, but women's are typically smellier - and that characteristic smell is formed chiefly by trace amounts of hydrogen sulphide. We produce precious little of this 'rotten-egg' gas (farts are mostly hydrogen, carbon ­dioxide and, in a third of us, methane), but we're extraordinarily sensitive to it because it is poisonous. Not at farting levels, fortunately. Farm workers are killed every year, however, when entering manure pits - a death cruelly dubbed 'dung lung' by doctors. Tragically, the gas paralyses the sense of smell at higher concentrations, and whole families have died trying to pull relatives from apparently odourless dung heaps, in catastrophic chains of hydrogen-sulphide poisoning.

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That idea runs dangerously close to farce. But behind the humour, much of what Roach says is important. We swill with mouthwashes that are less effective as antimicrobial agents than our saliva. We buy cereals bulked up with dietary bran that was the creation of flawed research, and has been ruthlessly exploited by the cereals industry.(In fact, slowing down your digestion - rather than speeding it up with bran - may protect against cancer. As long as it is inside you, not festering in a dung heap, hydrogen sulphide can help prevent inflammation.)

At least the fashion for Fletcherising has passed. Horace Fletcher (b1849), the well-connected but ill-informed nutritional expert of his day, advocated insanely thorough chewing of all foods, so as to produce a supposedly healthful "few dry balls once a week". His adherents included John Harvey Kellogg, of cornflake fame, Henry James, Sir Arthur Conan Doyle and Franz Kafka. The masticatory habits of the last were so unappealing, apparently, that the writer's own father hid behind a newspaper at ­dinnertime.

We all have our mad modern habits, though. We spend fortunes on pseudo-scientific 'probiotic' drinks containing aerobic strains of bacteria that are cheap to produce, which scientists believe are likely to be quite different from the anaerobic ones that actually do all the good work in the oxygen-free colon. Many people have enemas to remove 'toxins' from their colons, when there is no evidence that the colon can absorb anything harmful from faeces - and there is plenty of evidence that 'internal flushing' forces residues into higher portions of the gut, where they may, in fact, do harm. The absurd fashion for coffee enemas, meanwhile, has resulted in trips to A&E for more than one self-administrator labouring under the misapprehension that the coffee needed to be hot.

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Roach is a scientist at heart, and loves to debunk. The most extravagant myth in her book, however, she confirms. It concerns Elvis. The awful truth isn't simply that he died on the lavatory, which is well known. According to experts interviewed by Roach, he suffered from colonic inertia so crippling that it caused him severe constipation. A doctor present at the autopsy actually saw his vastly distended 'megacolon' - an organ so capacious that it would have explained Presley's apparent weight fluctuations. It would also have crowded his diaphragm and thus diminished his voice. With such an organ to contend with, straining could have been so extreme as to put pressure on his heart, arresting blood flow, causing his blood pressure to spike then plunge, and disturbing the heart's electrical rhythms - fatally.

If you find that story distasteful, you will probably find this book hard to, ahem, stomach. Even if you don't, there are reasons to dislike it. Roach pauses in her journey along the alimentary canal to interview a sequence of scientists, awarding them the sassy pen-portraits typical of American journalism. She describes a researcher into taste as looking "at once like someone who could have worked as a runway model and someone who would be mildly put off to hear that". That's a one-liner for GQ, not New Scientist - still less for a decent book. Worse, the experiments she performs alongside her chosen scientists sometimes feel they are done in the service of ­comedy, not science - as when she puts her arm right inside a fistulated cow, or asks the world's leading scientist on ­flatus if she can try on his fart-trapping Mylar pantaloons.

Roach is usually funny enough to get away with it, though. Her footnotes alone are worth the price of the book. Try the (unprintable) one about the Portuguese translation of the Bristol Stool Scale or the one (too long to print) about how she found glitter in her library copy of Inner Hygiene. Try listening to Lucy in the Sky with Diamonds in the same way now that you've heard the misheard line, "the girl with colitis goes by" (for "kaleidoscope eyes", of course).

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Ultimately, Roach pulls off the serious stuff, too. She forces us to reimagine ourselves not as spinal, brain-driven bipeds, but as a splendid digestive tube that has evolved limbs, brain and everything else, all the better to feed itself. She persuades us to admire, if not quite love, the dark thing that lies at the very core of us.

Gas - no laughing matter.

One of the more perilous intestinal hazards described by Mary Roach is the removal of colonic polyps with an electrical charge - which risks igniting methane or even hydrogen in the patient. In 1977, a man in France died from such a procedure because he had been prescribed a laxative that had produced, writes Roach, enough hydrogen 'for an internal Hindenburg'.

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(NY Times)

An Italian saliva expert named Erika Silletti recently addressed a dental conference. History doesn't record which aspects of saliva she extolled from the stage that day. Perhaps she described how art conservators are so enamored with its cleaning power they use it to dab fragile artworks. (Dishwashing detergent is a kind of simulated saliva, digesting the food you couldn't stomach.) Or maybe she praised the people of Greece - who spit on everything as a sign of good luck - for their saliva-positive attitudes. What we do know is that her speech was a bit of a disaster. The assembled dentists regarded her blankly. She returned to her hotel room and burst into tears. "They think of it as lubricating, and that's it!" she complained to her boyfriend.

The Mary Roach who discovered Erika Silletti ("while roaming the abstracts of a dental conference") and makes her such a heroic figure is the Mary Roach I love. Delightful, eccentric scientists, besotted by their spheres of study, light up her pages. So does her childlike wonder for the intricacies of the human body - how it whirs along, keeping us safe for the most part. Over the years she's explored the processes of human decomposition (Stiff), sex (Bonk) and the possibility of an afterlife (Spook). This time, with Gulp, it's the digestive system.

"Like a bite of something yummy," she promises, "you will begin at one end and make your way to the other." A clever conceit, but I wish she'd retained a little narrative mystique. Sure enough, we follow our food from the smelling, the tasting and the swallowing, inexorably downward, "via a stadium wave of sequential contractions, into a self-kneading sack of hydrochloric acid and then dumped into a tubular leach field, where it is converted into the most powerful taboo in human history." The taboos have worked in her favor, she writes. "The alimentary recesses hide a lode of unusual stories, mostly unmined."

Take flatulence. Flatulence could - according to an Alabama snake digestion expert named Stephen Secor - explain one of civilization's most enduring legends. A giant python eats a decomposing gazelle. It dies near a fire. A human steps on it. Hydrogen whooshes out of its mouth and catches light. Perhaps this is how the myth of the fire-breathing serpent came to be. "The oldest stories of fire-breathing dragons come from Africa and south China," Roach writes, "where the giant snakes are."

There is much to enjoy about Mary Roach - her infectious awe for quirky science and its nerdy adherents, her one-liners, that giant snake hypothesis. She is beloved, and justifiably so. Which is why I feel churlish, and weirdly guilty, for not enjoying Gulp more. Take the frequent, and really quite juvenile, medical student gallows humor. She seems quite over the moon about a Frenchman whose stomach exploded as a result of a botched colonoscopy in 1977. For her this was an "internal Hindenburg scenario," the colonoscope was "launched from the rectum like a torpedo." Terrible deaths are scattered for amusement throughout the book. In Philadelphia's Mutter Museum, Roach sees a photograph of a man soon to die from a hugely engorged colon. He reminds her of "the bastard offspring of Humpty Dumpty and Olive Oyl. . . . The cheesecake pose invites you to stare, but everything else says, Look away." I don't want to be a sourpuss for not finding it hilarious that sometimes people's stomachs explode, but I can think of a third response alongside "stare" and "look away." It's "sympathize." At such moments, Gulp is a bit too much like a highfalutin Ripley's Believe It or Not! for my liking - a lot of digestive system trivia but not much heart.

But Roach did sideswipe me with an enthralling chapter on "the alimentary canal as criminal accomplice." At a California prison she learns of an inmate who managed to get two boxes of staples, a pencil sharpener, sharpener blades and three jumbo binder rings up his "prison wallet" - jailhouse slang for rectum. His prison nickname became O.D., for Office Depot. She investigates how much damage a terrorist might do if he decided to swallow explosives - or have them surgically implanted - before getting on a plane (something Osama bin Laden apparently considered, according to documents found in his compound). The answer: almost no damage at all. Even a rectal bomb would do no more than blow the seat apart. All this is vintage Roach, as charmingly curious as the lab-nerds she eulogizes so affectionately.

But the main problem with Gulp is that in contrast with death and its aftermath - or sex, unfortunately, for many - we are already very closely acquainted with our digestive systems. There's the disappointing sense that for every promised unusual story we get a lot of stuff we already know or will just find quite unremarkable. I don't need to be told that the human tooth has an awesome ability to detect the tiniest grain of sand. It's no surprise to learn that when we sense an assault by some alien invader, like vinegar, we instantly deploy our saliva foot soldiers to dilute and disempower the acid. We live with our saliva and our flatulence and our gastric juices every day. Especially gastric juices, in my case. I am a chronic reflux sufferer. It is forever bubbling upward when it should bubble downward. I ought to have torn through the chapters relating to stomach acids. But what do I get? Roach asks someone to dab some hydrochloric acid on her hand so she can experience gastric acid. Nothing much happens. After a few minutes there's a mild itch, which then fades. Then we learn that mealworms don't dissolve in the stomach because they're protected by an exoskeleton. This is all perfectly fine, but doesn't live long in the imagination.

And I really could have done without her opening chapter - a day at an olive oil tasting center. It's so uneventful her usually enchanting asides feel strained to the breaking point: "I was right there with the numb-nose who wrote, on his answer form, "Oh, for a piece of good bread!" " she remarks. Her take-away, by the way, is: "Proficiency builds with exposure and practice." On occasions like this I'm afraid I found myself wondering how many more pages until I reached the colon and the excrement.


"People are surprised to learn: They are a big pipe with a little bit around it," says one of the many colorful scientists that populate Gulp, an odyssey through the digestive system by Mary Roach. Roach guides the reader gently down the upper reaches of the alimentary canal like a trustworthy gondolier before hitting the bawdy, chaotic rapids nearer the end of the journey.

Starting in the mouth, Roach skewers the maladaptive Western taste for protein-rich but nutritionally deficient animal parts - our preference for the bland comfort of a chicken breast over the complex, multivitamin-like offerings of liver, lungs, spleens, and brains that indigenous cultures still enjoy. In the mouth we meet scientists who have dedicated their lives to the mechanics of chewing and the chemical makeup of human saliva. (Our intuitions that saliva is a great stain-remover are confirmed: Saliva enzymes have been isolated and employed as active ingredients in high-end laundry detergents.)

Things get more exciting once we enter the stomach. Death by overeating, Roach informs us, is a real, if astronomically rare, phenomenon suffered not only by Monty Python characters but by gluttons with an affinity for postprandial alka-seltzers (the gas created by the antacids can be, in extreme circumstances, the straw that breaks the camel's stomach).

But it is the characters we encounter along the way that make Gulp so much nauseating fun. In the ghoulish 19th-century tale of surgeon William Beaumont and his adopted test subject Alexis St. Martin, we find consolation for the dysfunctional relationships in our own lives. St. Martin was a French Canadian trapper who, thanks to a blast of duckshot to his gut, had an open hole in his abdomen that gave Dr. Beaumont easy access to the roiling inner-workings of his stomach. Beaumont’s experiments on the hapless Canuck were bizarre to say the least (“On applying the tongue to the mucous coat of the stomach, in its empty, unirritated state, no acid taste can be perceived.”)

But in Gulp, as with partly digested food, after the pyloric sphincter, the gateway to the small intestine, there's no turning back. When Roach hits her stride in the intestines and onward, it's exhilarating to watch her gleefully trespass every taboo thinkable - and some that likely never occurred to the prim imaginations of most readers: shit eating and its spurious cousin, defecation by mouth; holy water enemas; the superhuman feats of rectal flexibility performed by human drug mules and prison contrabandists; and fatally explosive flatulence, to name a few.

Some episodes read like Jackass skits recounted in the clinically understated style of 19th-century physicians. Whether you will enjoy this book depends on your reactions to the following representative quotes. Roach pulls the first from the June 1874 Atlanta Medical and Surgical Journal as Dr. Robert Battey describes his great innovation in breaking up impacted masses in the colon, namely, injecting up to three gallons of water into the rectum: "So great was the abdominal tension that the water spouted from the anus when the pressure was removed in a bold stream," more than two feet high.

An 1871 issue of the British Medical Journal (the 1870s were evidently a golden age for this sort of thing) suggests another treatment for intestinal blockages: the application of an electric current to a patient's abdomen. "Efficacious?" a raffish physician is quoted in the Journal. "I could hardly get out of the way in time."

On that subject Roach also offers up what would seem to be the definitive account of Elvis' death. While it has the air of an urban legend, Roach settles the question of the King's demise - death by constipation - at the same time warning this reader, at least, of the overlooked scourge of defecation-associated sudden death, the perhaps not-so-silent killer.

Every journey must end, though, and Roach's voyage through the alimentary canal ends on a somewhat serious matter: the cutting-edge science behind the fecal transplant (what it sounds like) and the regulatory morass and squeamishness that hold back this apparently transformative procedure. Roach describes the almost miraculous relief of intestinal suffering experienced by patients infected with C. difficile - a potentially fatal condition that causes bouts of severe colitis and diarrhea. Thanks to the timely injection of someone else's you-know-what, these patients' bacterial gut flora is restored, as is their health. The clinical trial for treating C. difficile took a year and a half to gain approval from a university review board, and final FDA approval, the kind that would bring the procedure to the masses, could take more than a decade, Roach says.

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