IELTS Academic Reading Practice Test 331

For several centuries the standard medical textbook in European universities was written by a man who never visited Europe. Ibn Sina, known in Latin as Avicenna, was born in 980 in Afshana, a village near Bukhara in what is now Uzbekistan. His father, a local official, made sure that his son received an unusually thorough education. By the age of ten the boy had memorised the Quran, and he then studied logic, mathematics and jurisprudence. In the short account of his life that he dictated to a pupil, medicine proved the least difficult of the subjects he attempted.

Avicenna is said to have begun treating patients at sixteen, and to have acquired such a reputation that the ruler of Bukhara, Nuh ibn Mansur, called on him when his own physicians had failed. The reward was access to the royal library, where the young man read books that few scholars had ever seen. When the library burned not long afterwards, rivals are said to have accused him of starting the fire so that its contents would be known to him alone. Whatever the truth of the charge, the library gave him a command of Greek, Indian and Persian medical writing that shaped everything he later composed.

The world in which he made his name was, however, collapsing. The Samanid dynasty fell at the end of the tenth century, and Avicenna spent the rest of his life moving between courts, earning his living as a physician, an administrator and occasionally a political adviser. He passed through Gurganj, Gorgan and Rayy before settling for a time in Hamadan, where he served as vizier to the ruler Shams al-Dawla. Court politics brought him imprisonment at least once, and much of his writing was done while travelling or in hiding.

It was during these unsettled years that he assembled the work on which his European reputation rested. The Canon of Medicine, completed in about 1025, is an encyclopaedia in five books. The first sets out general principles, including the theory of the four humours inherited from Greek medicine and the belief that health depends on their balance. The second is a materia medica, a catalogue of simple drugs taken from plants, minerals and animals and arranged in alphabetical order. The third describes the diseases of each organ in turn, working from head to foot, while the fourth deals with fevers, surgery, wounds and poisons. The fifth is a handbook of compound remedies made from several ingredients, of which the most elaborate was theriac, a preparation with dozens of components.

What distinguished the Canon from earlier compilations was less the originality of its theory than the order and judgement it imposed on a vast inheritance. Avicenna accepted much of Galen, yet he did not hesitate to disagree with him, and he drew on Indian and Persian practice as well as Greek. He discussed how the effects of a remedy might be assessed, suggesting that a drug should be given to a patient in its natural state, observed over time and tried in more than one case before its value was accepted. He also considered how disease passes between people, noting that tuberculosis could be transmitted from the sick to the healthy.

The Canon reached western Europe through translation. In the twelfth century Gerard of Cremona, working in Toledo in Spain, turned it into Latin, and versions in Hebrew followed. Its systematic arrangement suited the medical schools that were then emerging, and it became a set text at universities including Montpellier and Padua. Printed editions appeared in the second half of the fifteenth century, and the work was still being taught in the seventeenth, when the anatomy of Vesalius and William Harvey's account of the circulation of the blood, published in 1628, undermined its authority. Even then it did not vanish: it remained in use in parts of the Islamic world for considerably longer.

Avicenna was not only a physician. His Book of Healing, a vast philosophical encyclopaedia, covered logic, physics, mathematics and metaphysics, and its influence on medieval European thought was considerable. He wrote poetry and treatises on music and on the formation of mountains. His output was prodigious, although not every work attributed to him is certainly his, and scholars still dispute the authorship of some texts. He died in 1037 at Hamadan, in present-day Iran, after an illness that later accounts say he treated too vigorously, and his tomb there remains a place of pilgrimage.

The Canon's long life is a reminder that knowledge does not travel in one direction. Its pages preserve Greek theory, Indian drugs and Persian practice, reorganised by a scholar working in Central Asia and Iran and then carried back into the European curriculum. For a modern reader, the most striking feature of the book is not its errors but its ambition: it tried to hold the whole of medical knowledge between five covers.

Modern historians of medicine are divided over Avicenna's originality. Some see him chiefly as a compiler whose genius lay in arrangement; others point to his insistence on observation and to the care with which he set out how a treatment should be tested. Both readings agree on one point: for half a millennium, anyone who studied medicine in Europe studied him. In Iran his name is still attached to a mausoleum, a university and an institute devoted to traditional medicine.

Digestion is often imagined as something that happens in the stomach, but the stomach is only one stage of a process that begins before the first mouthful is swallowed and may continue for more than a day. The organs responsible form a continuous tube, the alimentary canal, which in an adult runs for about nine metres from the mouth to the anus, with the liver, the gallbladder and the pancreas attached to it and supplying substances that the tube itself cannot produce. Food is broken down in two ways: mechanically, by chewing and by the muscular contractions of the gut wall, and chemically, by acid and by enzymes that split large molecules into smaller ones. Only when the molecules are small enough can they cross the wall of the gut and be used for energy, growth and repair.

The process starts in the mouth, where the teeth cut and grind food into pieces small enough to swallow. Chewing also breaks the food into smaller particles, which gives enzymes a larger surface on which to work. Three pairs of salivary glands release between one and one and a half litres of saliva a day; it moistens the food, contains mucus that makes the resulting bolus slippery, and carries an enzyme, amylase, which begins to break starch into simpler sugars. The tongue shapes the mixture and pushes it to the back of the throat. As swallowing begins, a flap of tissue called the epiglottis closes over the airway, so that food is directed into the oesophagus rather than into the lungs.

The oesophagus is a muscular tube about twenty-five centimetres long. It does not depend on gravity: rings of muscle above the food contract while those below relax, producing a wave called peristalsis which carries the bolus downwards in a few seconds. The same kind of movement, though slower, continues throughout the gut. At the lower end of the oesophagus, a ring of muscle acts as a valve, opening to let food into the stomach and otherwise preventing the acidic contents of the stomach from rising back into the tube.

The stomach is a muscular bag that can hold well over a litre. Its glands secrete hydrochloric acid, which gives the contents a pH of between about 1.5 and 3.5, together with pepsin, an enzyme that attacks proteins. Vigorous churning turns the food into a soupy liquid called chyme. A layer of mucus protects the stomach wall from being digested by its own secretions, and a valve at the lower end controls emptying, so that chyme enters the small intestine gradually rather than all at once. A few substances, among them alcohol and some drugs, are absorbed through the stomach wall, but most absorption happens further on.

Almost all chemical digestion and most absorption take place in the small intestine, which is about six metres long and is divided into three sections: the duodenum, the jejunum and the ileum. As chyme arrives, the pancreas delivers a juice containing enzymes for starch, protein and fat, while the liver produces bile, stored in the gallbladder, which breaks fat into tiny droplets so that enzymes can reach it. The inner surface of the intestine is folded into finger-like projections called villi, and the cells covering them carry further microscopic folds. The effect is to give an absorbing surface of many square metres, across which nutrients pass into the blood and lymph.

What remains passes into the large intestine, or colon, which is about one and a half metres long. Its main task is to recover water and salts from the residue, turning a liquid into a solid. Water is drawn back so efficiently that only a small fraction of the liquid entering the colon leaves it. The colon also contains an immense community of bacteria, which ferment material that the body's own enzymes cannot digest, including some forms of fibre, and produce vitamins that the body then absorbs. Movements of the colon push the waste slowly towards the rectum. The whole journey from mouth to exit usually takes between one and three days, though the range in healthy people is wide.

Many details remain uncertain. Transit time varies enormously between healthy individuals, and no one can say precisely why. The gut has its own network of nerve cells, estimated at several hundred million, which can coordinate movement without instructions from the brain, and how far this enteric nervous system acts independently is still debated. The composition of the gut bacteria differs strikingly from one person to another, and researchers cannot yet say which patterns should be considered healthy. Signals passing between the gut and the brain are also under investigation, although claims that bacteria control mood are far ahead of the evidence.

Some of the most promising research concerns the bacteria themselves. Faecal microbiota transplantation, in which stool from a healthy donor is transferred into a patient's gut, is now an accepted treatment for repeated infection with a bacterium called Clostridioides difficile, which can take hold after antibiotics have wiped out the normal gut community. Whether the approach can be adapted for other conditions, from inflammatory bowel disease to metabolic disorders, is being tested in trials, but the results so far are mixed and the procedure is not without risk. Researchers are also trying to work out which components of the diet feed the most useful bacteria.

A walk down the drinks aisle of any supermarket reveals a section designed to catch the eye: tall cans in fluorescent colours, names suggesting speed and power, and slogans about energy and alertness. A 500-millilitre can of this kind typically contains around 160 milligrams of caffeine, roughly the amount in two cups of coffee, along with sugar, taurine and B vitamins. The appeal is not accidental. The names, colours and promises are aimed at a young market, and surveys suggest that a substantial minority of adolescents drink such products regularly. Whether the state should stop them is a question about markets as much as about medicine.

Caffeine is a stimulant. It blocks a chemical in the brain that normally makes us feel sleepy, and in doing so it raises alertness and blood pressure. It also stays in the body for hours: the half-life in a healthy adult is usually given as five to six hours, so a can drunk at four in the afternoon is still partly present at bedtime. In 2015 the European Food Safety Authority reviewed the evidence and concluded that single doses of up to 200 milligrams, and daily intakes of up to 400 milligrams, do not raise safety concerns for healthy adults. For children and adolescents it proposed a much lower figure of 3 milligrams per kilogram of body weight a day. A child weighing 30 kilograms therefore reaches that level with about 90 milligrams, only a little more than the 80 milligrams in a single small can.

Sugar is the second issue. A large can may contain 50 grams or more, while official advice in Britain is that a primary-school child should take in less than 25 grams of free sugars a day from all sources combined. Regular consumption is associated with tooth decay and with weight gain. Yet energy drinks are not the main source of sugar in young people's diets: soft drinks, confectionery and breakfast cereals contribute much more, and sugar-free versions of the same brands are now widely sold. A policy aimed only at these cans would therefore miss most of the sugar that children consume.

Opponents of restriction make three arguments. The first places responsibility on parents, who can refuse to buy the drinks and can tell their children not to. The second is practicality: an age limit is difficult to enforce when thousands of small shops sell the products, and a teenager can ask an older friend to buy on their behalf. The third is substitution: a child who cannot buy an energy drink may simply drink cola or coffee, which also contain caffeine. Each argument has force, but each assumes that nothing else can change. The first, in particular, mistakes formal responsibility for practical control.

Some governments have decided that something should change. Two Baltic states, Lithuania and Latvia, have restricted sales to minors, and several other countries have debated similar steps. In Britain the government consulted in 2018 on ending the sale of energy drinks to children under sixteen. What is striking is how little is known about the results: very few published studies have attempted to measure whether such restrictions reduce consumption, and none has yet produced firm evidence.

Labels are supposed to inform. Under European rules, a drink containing more than 150 milligrams of caffeine per litre must state that it has a high caffeine content and is not recommended for children. The wording is there, but it is printed in small type on the back of the can, and shoppers choosing a drink in a hurry rarely read it. A further confusion is that energy drinks are often displayed beside sports drinks, which are intended to replace water and salts lost through exercise and may contain no caffeine at all. The two categories look alike and are widely assumed to do the same job.

Some institutions have acted without waiting for national policy. A number of schools have banned the drinks from their premises, and several retail chains have set their own age limits at the till. Whether schools have moved faster than retailers is impossible to say, since neither group reports its experience in a comparable way and the policies themselves differ in detail.

My own view is that the case for a modest restriction is strong, but that a restriction on its own would achieve little. Children's choices are shaped by price, by display and by advertising, and a rule that applies at the till does nothing about any of these. A workable policy would combine an age limit with limits on marketing aimed at the young, clearer front-of-pack labelling of caffeine content, and a price that reflects the sugar in the can. The objection that such measures are paternalistic seems to me weak: the state already sets age limits for tobacco, alcohol and gambling, and it does so because children's judgement is not yet reliable and because the market has an interest in exploiting it.

The debate, then, is not really about whether caffeine is dangerous. It is about who sets the terms on which a product aimed partly at children is sold. An imperfect restriction, honestly evaluated and adjusted in the light of evidence, seems to me a better answer than either an unregulated market or a ban that no one checks. What matters is that the policy is monitored, so that the next generation of decisions rests on evidence rather than on assertion.