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Whenever I have the misfortune to be sick, I experience a sensation
of utter alienation. It is as if my body is no longer my own. At the time,
I almost feel that I’d rather be dead than taken over by this alien spewing
monster. Can you offer me any help? Yours pallidly, Gus

* * *

Dear Gus,

Precious little I’m afraid. The reason for your alienation lies in the
mechanism of vomiting and its consequences. Essentially you are being taken
over, but only by a part of the brain – and in a good cause. If you can
shift your outlook towards greater objectivity, you will soon come to appreciate
the awesome power and strange elegance of the vomiting process.

When you eat something noxious – poisoned by bacteria, say, or otherwise
contaminated – chemical sensors in the stomach alert the brain to the danger.
From then on, you are, so to speak, on autopilot. A cascade of survival
mechanisms switches on, under the control of the brain stem. The stomach
stops churning and squeezing; you begin to feel strange, but the poison
has at least been contained. The small intestine may reverse its usual movements
to bring suspect food back to the stomach. Disagreeable sensations come
thick and fast: clamminess, salivation, yawning and pallor are the most
obvious.

The real work begins. You take a deep breath, open the muscles at the
top of the gullet and shut off the airway to the lungs for protection. Similarly,
you close the passage between throat and nose, thereby ensuring that you
cannot be sick through your nostrils. The duodenum goes into spasm, sealing
off the normal exit from the stomach. The abdominal muscles contract, as
does the diaphragm, squeezing the bloated stomach between them, like a bag
of icing between a cook’s fingers. If retching is prolonged, the vomit may
swill back and forth in the gullet before a final push sends it into the
world. Meanwhile, there may be further instalments brewing. In severe cases,
bile from the duodenum floods back into the stomach and gives a green-yellow
tinge to the vomit.

As these details show, spewing is an act that requires careful coordination
and split-second timing. Instructions to the muscles and viscera are dispatched
via five cranial nerves and various routes along the spinal column. Your
body occasionally needs to turn the clock back on a meal; it does so automatically
and with ruthless skill.

Just occasionally, vomiting comes out of the realm of the automatic
and people learn how to put it to work. A notable instance arose in the
17th century in the shape of Floram Marchand, an entertainer who claimed
to vomit various alcoholic drinks at will. Marchand would begin by drinking
a vast amount of tepid water – 24 glasses, it was said – distending the
stomach and triggering vomiting. As the fluid emerged he would fill successive
glasses with ‘claret’, ‘beer’, ‘white wine’ and so on. Marchand was something
of a chemist. Before performing, he fasted and then drank an extract of
brazil wood – a substance that contains a yellow dye. The dye, brazilin,
changes colour according to the acidity of its surroundings. So, to produce
the correct hue, Marchand directed his vomit into a glass that had been
treated with an appropriate acid. Even so, there must be easier ways to
earn a living.

Yours sincerely, Constance

Dear Constance,

I’ve had two healthy babies and each time I’ve been sick in early pregnancy.
Now that I’m thinking about starting a third, I’m steeling myself for another
onslaught. My question is this: How can a tiny embryo 2 millimetres in length
have such an unwholesome influence on a being 1000 times its size? Yours
gravidly, Antonia

* * *

Dear Antonia, Morning sickness is not so much a solo performance by
your baby as a vast and complex hormonal tutti played by your entire body.
Although it feels dreadful, a modicum of sickness is traditionally regarded
as a sign of a healthy, stable pregnancy. It is remarkably common. According
to a new study by Paul Andrews and Saffron Whitehead at St George’s Hospital
Medical School in London, it occurs in three-quarters of pregnant women,
and not just in the morning. Much of the responsibility for this state of
affairs lies with the sex hormones, oestrogen and progesterone. Sex hormones
can spark off nausea and vomiting in other circumstances too, notably among
users of oral contraceptives.

The link between sex hormones and sickness is anything but direct. Andrews
and Whitehead believe instead that the hormones exert their effects by sensitising
a part of the brain known as area postrema. The area postrema is a chemical
early warning station, responsible among other things for detecting noxious
chemicals in the blood and cerebrospinal fluid. Once triggered, its job
is to arrange a bout of vomiting – with the aim of ridding the body of a
stomach-load of suspect food. Any increase in sensitivity, due to hormones,
could make vomiting just that little bit more likely. Andrews and Whitehead
contend that this state of affairs benefits a mother-to-be because it provides
her fetus with extra protection against poisons. Nausea prompts many pregnant
women to give up coffee, alcohol or tobacco.

Sex hormones are not the only part of the mechanism. Pregnant women
also experience massive upheavals in the chemistry of the digestive tract,
according to Kerstin Uvnas-Moberg and colleagues at the Karolinska Institute
in Stockholm. Among these changes is an increase in the production of a
gut hormone called cholecystokinin (CCK). One of CCK’s normal jobs is to
control emptying of the stomach so that food trickles at a judicious rate
into the small intestine and does not swamp the system. Higher levels of
CCK mean that food stays in the stomach for longer. This gastric go-slow
may well contribute to the feeling of nausea. The moral seems to be: if
you feel sick, blame your food, not your fetus.

Yours sincerely, Constance

Dear Constance, As an unabashed sybarite, I am often required to gorge
myself on enormous meals, drink rivers of wine and generally indulge myself
to excess. In true Roman style, I regard being sick as something between
an occupational hazard and a necessity for continuous consumption. However,
as I grow older, I confess to finding vomiting something of a strain and
I would welcome any reliable prophylactic. Yours orgiastically, Claude

* * *

Dear Claude,

Oh dear, I was afraid someone was going to ask me that. How about eating
less? When you pack your paunch to overflowing, you stretch the stomach
wall and excite special mechanical sensors. These send alarm signals to
the brain, which orders an immediate evacuation. Rivers of wine can have
the same effect.

There is simply no real protection unless you eat sensibly and refrain
from tickling the throat with a feather. You have to view vomiting as part
of your defences, a part every bit as important as your immune system, or
your taste buds. If you ignore the warning signs and go on with the mushrooms
and chianti until fit to burst – well, you only have yourself to blame.

Although ruled out for trenchermen like yourself, drugs that prevent
vomiting are of major importance in medicine. Their chief role is in the
management of cancers, where radiation or chemotherapy can bring on well-nigh
unbearable nausea and vomiting. New ideas about the underlying processes
have come out of a series of experiments by Paul Andrews at St George’s
Hospital Medical School in London, together with teams led by Chris Davis
at the University of Oxford, Gareth Sanger at Beecham Pharmaceuticals, Brenda
Costall and Robert Naylor at the University of Bradford and Mike Tyers at
Glaxo. The research suggests that cancer therapy prompts the release of
a substance called 5-hydroxytryptamine (5-HT) from cells lining the alimentary
tract. This substance acts on nerve endings in the tract, causing alarm
signals to be sent to the brain, where they trigger lengthy sessions of
vomiting.

There are likely to be other pathways at work too, such as a direct
effect of 5-HT on the brain. Whatever the exact mechanism, drugs that block
these actions of 5-HT are proving highly effective at relieving the misery
of endless nausea.

Yours sincerely, Constance

Dear Constance,

My biology teacher taught me that everything in nature served a purpose.
She had obviously never suffered from sea sickness. Every time I board the
ferry to visit my villa in Santander, I find myself on the toilet floor,
vomiting violently and wondering what it’s all for. The experience would
be just a mite less demeaning if I could see some chink of sense in the
whole dark business. Yours wretchedly, Julius

* * *

Dear Julius,

You are choking on one of the great unsolved problems in physiology.
However, there is a good theory on the subject, which was first suggested
more than a decade ago by Michel Treisman, a psychologist from the University
of Oxford. It goes something like this: as you roll and pitch across the
Bay of Biscay, your brain is being fed with indigestible information from
the various sensors that monitor posture and balance. By an unfortunate
coincidence, this information mimics the effects of eating food contaminated
with certain nerve poisons. You are sick because evolution, in its unrelenting
wisdom, has equipped you with the wherewithal to empty your stomach in such
unhealthy circumstances.

Is there any way of outwitting evolution? You could try to acquire some
resistance by surreptitiously practising on the swings and roundabouts in
your local playground, but the chances of success are slim. People who adapt
to one variety of motion often find themselves suffering all over again
when exposed to a new variety.

Once on board ship, you can sample other remedies. Some people find
it helpful to sit on deck and keep watch of the horizon, thereby providing
themselves with a reliable frame of reference. Alternatively, you can lie
down and hold your head as still as possible, so as not to overstimulate
the sensitive semicircular canals in your ears.

If this fails, you may find some solace in the fact that you are in
distinguished company. By all accounts Charles Darwin spent the first three
weeks of his trip on the Beagle in a wretched condition and he suffered
dreadfully with each deterioration in the weather. Samuel Johnson and James
Boswell were both seasick during a wild nocturnal voyage in the Hebrides.
Boswell’s case was not eased by the mutton, herring and beer that he had
consumed for dinner.

T. E. Lawrence fell victim to motion sickness on a camel, proving once
again that the camel is aptly described as the ship of the desert. (Elephants
also provoke motion sickness, but horse-riders are oddly immune, presumably
because their progression is smoother.) As a final crumb of comfort, consider
the cod: a fish that gets seasick when transported in a tank on board ship.
There is clearly no disgrace in your affliction.

Yours sincerely, Constance

Dear Constance,

Life is so unfair. The rat lives in sewers, swims in human excrement,
eats filth and breeds on rubbish tips. I live in a spotlessly clean house,
take a daily bath and treat chicken casserole as a microbiological hazard.
Yet rats are never sick, while I throw up all over the kitchen at the slightest
whiff of fried sausage. Yours queasily, Marcia

* * *

Dear Marcia,

Fried sausages notwithstanding, I am not convinced that we have such
a raw deal. It is true that many creatures, rodents included, do not vomit,
but this can be something of a mixed blessing. The rat is a case in point.
Part of its reluctance to vomit stems from the nature of the muscle guarding
the entrance to the stomach. By all accounts, the muscle acts as a one-way
valve. As a result, a rat cannot empty its stomach if it has the misfortune
to eat an emetic or suffers an intestinal blockage. Eventually, the stomach
may rupture under the strain.

Yet rats are rarely inconvenienced by this apparent defect. Despite
their noisome haunts, they are intensely wary about their diet. They sample
a small morsel of anything new and wait to see if it affects them adversely
before returning for more. In a sense, they bypass the need to vomit.

Horses are also incapable of vomiting and, like the rat, they risk rupturing
the stomach. They suffer an additional indignity if they eat when the gullet
is obstructed as the result of illness: food reappears from the nose. Ruminants
are rarely sick, yet cows may vomit if they eat suspect silage. Unlike the
average ruminant, dogs and cats are no strangers to vomiting. They even
go so far as to seek out couch grass as a stimulus when the need arises.
Another carnivore, the ferret, has become a favourite in physiological circles
because its stomach – and its vomiting – has much in common with ours.

Vomiting is an activity that unites animals of all varieties. House
flies often bring up parts of one meal onto the next. Bees concentrate nectar
by repeatedly regurgitating it and letting it evaporate. Blue jays vomit
if they eat a poisonous butterfly. Some birds habitually vomit in self defence.
An army of creatures, from coyotes to diving petrels, feed their young on
regurgitated food.

Frogs are also prominent members of the vomiting fraternity, according
to recent studies by Tomio Naitoh and colleagues at Dalhousie University
in Halifax, Nova Scotia. Unlike human babies with their enthusiasm for vomiting,
tadpoles cannot be sick. Yet they soon make up for any delay once they reach
maturity. With frogs, as in humans, a key part of the mechanism is compression
of the abdomen. Some frogs squeeze the viscera between back and belly; others
achieve the same result by shortening the body to two-thirds of its usual
length. For frogs that brood tadpoles in the stomach, faulty food is not
the only reason for being sick; they must vomit forth their young at the
appointed time.

If you still think humans badly off, consider this final detail. Sometimes
a frog is so utterly sick that it brings up part of its alimentary canal
with its dinner. It then faces the extraordinary task of reswallowing its
own stomach. Anyone for sausages?

Yours sincerely,

Constance Pugh