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SECTION B
Text № 1 «WHY DO WE EAT?»
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No record exists to tell us who first began to think about why we eat or about various effects of foods, but the ancient Greek philosophers and doctors commented along these lines. Socrates said, the purpose of food is to replace the water lost through the skin and the loss of heat from the body. Hipocrates, the “father of medicine”, thought that growing bodies should have more heat than those of older people and so require more food, that neither overeating nor fasting is a good idea.
Lavoisier thought that the combustion1 that produces body heat should occur in the lungs, but later several chemists could show that the oxygen combines with the red corpuscles of the blood and is carried to the tissues in all parts of the body to supply energy where it is needed.
Understanding of the composition of foods and what happens to them after they are eaten had to wait for several discoveries in chemistry. What happens to food from the time it is eaten until it is oxidized to produce heat and mechanical energy, could not be learned until the chemical nature of foods was discovered. And the foods appear to be very complex organic substances.
Foods are composed of organic substances far too complex to be understood with the state of chemistry as it was in the first half of the nineteenth century. Modern work on digestion and nutrition began about a century ago.
Although scientists had attempted to learn why we eat, they could learn very little. We might sum up their accomplishments by saying they learned that all animals inhale oxygen, combine it with the food to produce carbon dioxide, heat, and the energy with which they could move about. The chemistry of that time could not tell more.
Now we know that we should eat to have energy. When the nutritionist uses the word “energy” he means the capacity to do work. To him “work” is movement. All work requires energy and work involves motion; therefore, the more a person moves about, the more energy he requires. Even when a man is asleep he is still partly in motion because his heart, lungs and most of the other organs are working.
1- combustion - сгорание
Text № 2 «SUGAR AND STARCH»
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Among common carbohydrates are sugar and starch. Although these substances differ widely from one another in properties and constitution, they show a very definite point of resemblance. They are all composed of carbon, hydrogen and oxygen, and the hydrogen and oxygen are always in the sane ratio to one another as in water, i.e.1, two of hydrogen to one of oxygen. The name, therefore, of carbohydrates was given because these compounds seemed to be built up of carbon and water in different proportions. Thus glucose, as sugar, has a formula C6H12O6 – which might be represented as 6C+6H2O. It may be pointed out that this last method of representation is only referred to for the purpose of showing how the name arose.
There is hardly a plant that does not contain either sugar or starch or cellulose or even all the three of them. The sugar and starches are among our most common foods, and the celluloses though not useful as a food, are found the main constituents of wood, paper, cotton and other fibres or fibrous materials.
Our ordinary everyday life leads us to think that there is only one sugar, viz2., that we use as a sweetening agent for tea. In fact there are many sugars, they are glucose (so called dextrose or grape-sugar), fructose (also called levulose) and galactose.
Glucose or grape-sugar is found in large quantities in grapes. When these are dried in the sun to form resins, the glucose in the juice separates out as hard brown nodules3. It is frequently found mixed with fructose in the juice of fruits, in the roots and leaves of plants and in honey. It can also be obtained from cane sugar and starch. Glucose is soluble in about its own weight of water and is not so sweet as ordinary cane sugar.
It readily ferments with yeast and yields principally alcohol and carbon dioxide.
Fructose occurs with glucose in the juice of sweet fruits and in honey. It is more soluble in water than glucose, and is about as sweet as the latter. It ferments with yeast but not as rapidly as glucose.
1- id est – то есть
2- viz.=videlicet – а именно
3- nodules – (зд.) масса=комочки
Text № 3 «ENERGY REQUIREMENTS»