What is blood pressure?

          The heart is a vital organ that pumps blood to different parts of the body. The outflow of the blood takes place when the heart’s left ventricle contracts. Then blood is forced into the arteries which expand to receive blood. These arteries have a muscular lining which resists this pressure. Thus blood is squeezed out of them into the smaller vessels of the body. By blood pressure we mean the amount of pressure that blood exerts on the walls of the arteries. The amount of pressure depends upon the strength of the heart muscle, the amount of blood in the circulatory system and the condition of the arteries. 





          There are two kinds of pressures – systolic and diastolic. Systolic is the maximum pressure that occurs when the left ventricle contracts. Diastolic is the minimum pressure that occurs just before the heartbeat which follows.



          When a doctor measures blood pressure, he uses an instrument in which a column of mercury rises or falls under the pressure. It is marked in millimeters. The average systolic pressure in a young man is about 120 mm of mercury and the diastolic pressure is about 80. These figures are usually stated as 120/80 or 120 over 80.



          Blood pressure usually rises with age because the arteries become less flexible. Anxiety or exercise may also cause pressure to rise temporarily. It is also increased by a number of diseases. A. person is said to have high blood pressure or hypertension if it exceeds the figure of 100 plus his age or if the diastolic pressure exceeds 100. High blood pressure can cause heart failure, apoplexy, or kidney diseases. It may also burst a blood vessel in the eye or the brain, thus causing blindness or a hemorrhage. Symptoms of high blood pressure are headaches, hot flashes and anger.



          Abnormally low blood pressure occurs when a person has a heart attack or loses large amount of blood because of some injury etc. When the blood pressure falls considerably, the oxygen supply to the brain and other parts also gets reduced. This can cause death. Physicians use drugs which contract the muscular walls of the blood vessels to raise the blood pressure.



          Abnormal high blood pressure may be due to the constriction of arteries or due to damage to one or both kidneys. Excessive weight and lack of exercise can also contribute to hypertension. Temporary high blood pressure can be due to excitement or emotional stresses.



 


What is the Iron-lung machine?


          The iron-lung machine was one of the earliest life-saving machines. It was invented by Philip Drinker of Harvard, U.S.A in 1929. This device is meant to aid those who have difficulty in breathing, either due to a paralysis of chest muscles or due to some disease or an accident.



         This machine has an air-tight chamber on wheels. The patient lies on a foam-rubber bed with an adjustable head and foot rests. It is operated by electricity, but has a safety device which gives a warning signal in the vent of power failure. The machine can then be operated by hand. It has a cover which can be opened to give access to the patient. The patient’s head is usually enclosed in a plastic dome.



          The machine helps in breathing by alternately reducing and increasing the air pressure around the patient’s body. When the pressure is reduced, his chest expands and air comes into his lungs through the normal air passages, as his head remains outside the machine. When the pressure is increased, the chest contracts and air is automatically expelled from the lungs.



          During a heart operation, a heart-lung machine is used. This takes over the function of the heart and lungs and the surgeon can perform the surgery safely. The technical name for this machine is the cardiopulmonary bypass machine, since it takes over the job of both heart and lungs. Blood returning along veins, from the body’s organs to the heart, is led out of the body along a tube to a gas exchange unit. Here carbon dioxide is removed from the blood and oxygen is added – thus doing the lung’s job. The blood then flows through a rotary pump which does the heart’s job and back into the main arteries. This is a very important device during heart surgery. 


What causes asthma?

          Asthma is a chronic disease of the lungs in which a person has sudden attacks of shortness of breath, wheezing and coughing. It is one of the most common diseases affecting respiration. It affects all races and both sexes equally. It usually begins in childhood or early adult life.

          Asthma is caused by a blocking of the bronchial tubes in the lungs. This blocking is caused by shrinking of the bronchial muscles, swelling of membranes lining these muscles and the presence of thick mucus called phlegm.



          Allergic bronchial asthma is the most common type of the disease. It is caused by adverse reaction to things like house dust, pollen, feathers, animal dandruff, drugs and certain foods. Strong odours or smoke may also cause its attacks. Asthma is often linked with however, another type of allergy. Different kinds of asthma may even harm other parts of the body. 





          Asthma attacks often occur after heavy physical work or in case of emotional disturbance. An infection of the nose and throat can trigger off an attack. A drastic change in the weather may also prove troublesome in this regard. Exposure to sudden changes in temperature and humidity or both may also cause an attack. Common symptoms of asthma are wheezing, a sense of suffocation, dry cough and an inability to expel air easily from the lungs.



          Asthmatic attacks usually last for half an hour to several hours. Prolonged or frequent attacks may prove dangerous if the patient is weak or suffers from malnutrition. Some 35-40 percent of childhood asthma cases improve at puberty.



           A physician identifies asthma by physical examination and allergy skin tests. From these tests, the substance to which the patient is allergic can be detected. Most doctors usually prescribe drugs such as epinephrine or ephedrine to treat it in the initial stages. Patients with very serious cases of asthma however may need to take ACTH or cortisone. Some doctors prescribe small doses or injections of asthma-causing substances. And they slowly increase the strength of these injections until the patient’s body develops a natural resistance to the allergic substances. Sometimes oxygen becomes essential for such a patient. To avoid asthma attacks one should avoid substances to which one is allergic and the situations that precipitate attacks.



 


What are the functions of arteries and veins in our body?

Blood must reach every cell in the body to provide it with food and oxygen, and to remove waste products. The group of organs which circulate blood through the body is called the circulatory system.



In the human beings, the circulatory system has a muscular pump called heart. It pumps the blood through long, tube-like blood vessels. Blood vessels carry the blood throughout the body to the cells. In our circulatory system there are five types of blood vessels: arteries, arterioles, capillaries, venules and veins. An artery is a large vessel that carries blood away from the heart to the cells. It branches off into the smaller arterioles which further divide into very small capillaries. The capillaries carry blood to the cells. These reunite to form larger tubes called venules. These venules merge to form large tubes called veins. Veins carry impure blood back to the heart. According to a rough estimate if all the blood vessels are joined together in a single-line they would stretch to 60,000 miles.



Blood is pumped from the right ventricle of the heart into the pulmonary artery. The pulmonary artery carries it to the lungs where it absorbs oxygen and releases carbon-dioxide. The blood returns to the left auricle of the heart through the pulmonary vein. The left auricle pumps the oxygenated blood into the left ventricle of the heart which pumps it into aorta. The aorta is the largest artery in the body. It carries blood to other arteries and arterioles. The blood absorbs food when it passes near the small intestines. The wastes from the cells are removed from the blood when it passes through the kidneys. After the blood passes through the cells of the body, delivering food and oxygen and removing wastes, it returns to the heart through the vena cava. The vena cava is the largest vein in the body. The unoxygenated blood enters the right auricle which returns it to the right ventricle. It is then pumped to the lungs to receive more oxygen.    



The muscular walls of the arteries are thick and elastic. They carry bright red, oxygen-rich blood. As the heart pumps, a wave of pressure travels along the walls of arteries and can be felt as pulse. Their walls can contract and release and can regulate the amount of blood flowing to the body tissues.



The walls of veins have three layers: elastic, muscular and lining. The veins are thinner and less muscular than the arteries. In the arms and legs the veins have valves that prevent the back flow and pooling of blood due to gravity. The veins that are swollen, stretched or coiled on themselves are called varicose veins. These can sometimes be found on the legs of older people as well as those whose jobs involve a lot of walking. Blood in the veins is under low pressure and flows slowly. Since it contains less oxygen, it turns purplish red in colour. 




What is the function of liver in our body?

          The liver is a large and vitally important organ in the abdomen. It can be thought of as a living laboratory and a chemical plant. More than hundred different processes are known to take place in it. It is reddish brown in colour and located in the upper abdominal cavity beneath the diaphragm and ribs.

          The liver is basically concerned with the digestion of food, excretion, storage and conversion of food materials, the regulation of the composition of blood and the destruction of poisonous substances. If it stops working, death is imminent within a few hours.



          In an adult person, the liver weighs about 1.5 kg. The liver is divided into two lobes – right and left. The right lobe is about three times the size of the left lobe. Pressed tightly against it is the gall-bladder. 


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What is allergy?

          Hay fever, rashes on the skin, reactions to certain injections (anaphylactic shock) and some types of asthma are the more common forms of allergy in man. What is an allergy?



          An allergy is an abnormal sensitivity of the body to certain substances especially proteins. In our environment different substances causing allergic reaction are present in countless forms. They may be in pollen or dust that enter the nose or eyes, in the serum of a vaccine or an antibiotic (such as penicillin), or in some food article. Some people are also allergic to feathers and bee stings. There are literally hundreds of allergens. 



          In an allergic reaction the substance causing the reaction is called allergen or antigen, and substances formed within the body during the processes of sensitization are known as antibodies. Though antibodies are one of our main defences against infection but in the event of an allergy they produce unpleasant reactions. The abnormal antibodies on coming in contact with an allergen such as a pollen or fungus, release chemical agents such as histamine, serotonin and other slow reacting substances. The release of these substances produces symptoms of allergy characterized by a running nose, rash and breathing difficulty. Some allergic reactions take several hours to develop while there are others which occur promptly and may cause unconsciousness or even death. They produce fall in blood pressure, difficulty in breathing and a bluish tinge in the skin. 





          It is believed that an allergic substance combines with its antibody and releases a substance called ‘histamine’ in the body. It is this histamine which acts on the blood or other parts and causes allergic symptoms such as sneezing, wheezing, shortness of breath, itching, swelling and redness of the skin. On the basis of this theory antihistamine drugs have been developed for the treatment of several types of allergic reactions. The first antihistamine drug was phyrilamine maleate and today there are wide ranges of similarly acting drugs. They block the action of histamines through their chemical structure.



          Antihistamines can be used to combat hay-fever, asthma, drug rashes, reactions to stings and vaccines. So far, scientists have not succeeded in developing medicines for acute allergic reactions. Development of specific antagonists of chemical mediators of the allergic reactions is required for rational therapy of these diseases. It is important to note that allergic diseases attributable to antigens in the environment are best controlled by avoiding or eliminating the offending substance.



          Medical sciences have yet not been able to explain why certain people are allergic to certain agents, and not others. According to many doctors and scientists heredity has a role in deciding who would be allergic and to what. 


What is blood cancer or leukemia?

          Leukemia or blood cancer is a fatal disease of the blood-forming tissues wherein abnormal white blood cells are found in the blood stream. It can occur at any age and in either sex. It is even more dangerous because its cause is still unknown. Do you know what happens in this disease?



          Blood is a vital body fluid and all its constituents have a specific function. Blood has a large number of red blood cells and a comparatively smaller number of white blood cells. The red blood cells carry oxygen to all the tissues of the body. The white cells defend the body. White blood cells are produced mainly in the bone marrow and lymph glands. In the case of leukemia, something goes wrong with the tissues that produce white cells. So these cells start multiplying at an abnormal rate. A person afflicted with leukemia may have 30 to 60 times the normal number of white blood cells that a healthy person has. Simultaneously, the rate of production of red blood cells becomes extremely slow and this causes anaemia. 


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What is albinism?

          Albinism has been derived from the Latin word ‘albus’ which means ‘white’. Albinism is an inherited disease caused by genetic changes. It can be passed on from one generation to another.



          Albinism is caused by the absence of yellow, red, brown or black pigments in the eyes, skin scales, feathers or hair. The natural pigments usually provide protective colouration and act as a screen against the light rays. Since albino animals lack them, they rarely survive in the wild.



          Albinos are found in plants, animals and human beings. In human beings, it is caused by the absence of melanin, the dark brown pigment normally present in the skin, hair and eyes. It varies from complete albinism to localized albinism or spotting.



          In the case of complete albinism, the person doesn’t have any pigment in any of their cells. They have milk-white skin and hair. Their eyes appear pink because of the colour of the blood vessels. Since the light-absorbing pigments are absent, an albino is extremely sensitive to bright light like that of the sun.



          In partial albinism, only some tissues and organs lack in pigment. Some animals are also partial albinos. One case of complete albinism is found in every 20,000 people.



          However some plants too, with white flowers, are partial albinos. A complete albino plant lacks even the green pigment - chlorophyll. As a result, it is unable to make its food by photosynthesis, and dies shortly after its food supply in the seed is exhausted.




How do urine tests help in diagnosis of diseases?

          Diagnosis of different diseases by urine examination has been a common practice since a long time. But the traditional methods were not very scientific as the modern methods. Although special urine tests in laboratory can reveal many diseases, even a casual examination can indicate certain diseases. Let us see how different urine tests help in diagnosing some diseases.

          Normal urine is straw yellow in colour due to the presence of the pigment ‘urochrome’. If a person has fever, it becomes deep yellow. In case of jaundice, it becomes still deeper in colour. Consumption of vitamin B-complex also makes the urine deep yellow. This is because of the presence of riboflavin in the tablets. If the colour of urine changes to brown or black due to atmospheric pressure, it indicates a congenital disease called alcaptonuria. If its colour is brown or black, it suggests derangement of haemoglobin metabolism.



          If the urine of a diabetic patient is left in the open for some time, it would attract ants. This is due to the presence of glucose in it. Its taste is also sweetish. To test the presence of sugar in urine, it is boiled with Benedict solution. If a red precipitate is formed, it indicates the presence of glucose. 



 


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What is the Theory of Relativity?


In the early nineteenth century people believed that light travelled through imaginary stationary medium called ether. It was believed that ether filled all space, and all movements could be measured absolutely with respect to it. It was also thought that the speed of light relative to a moving observer could be calculated in the same way as the relative speeds of any two moving objects. For example, just imagine two cars in the same direction: one going at a speed of 110 km/hr and the other at 80 km/hr. Passengers in the slower car would observe that the faster car is travelling at 30 km/hr.



Two American scientists, Michaelson and Morley, experimentally tried to measure the speed of earth through ether in 1887. But their result did not confirm the existence of the hypothetical medium ether. Later the explanation of negative results was offered by Albert Einstein. According to him, nothing like ether exists in the universe and the concept of absolute motion is meaningless. He also said that the speed of light is constant, no matter how fast the observer is moving. No material body can travel faster than light.



On the basis of his conclusions, Einstein formulated the Special Theory of Relativity in 1905. He showed that physical quantities like mass, length and time are also not absolute. They change as the bodies move. If a body moves with a large velocity, its mass increases and it becomes shorter. 


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How is nylon made?


            Nylon is one of the most important chemical discoveries of the 20th century. It is one of the toughest, strongest and most elastic substances we have today. It is a synthetic plastic material which is made from chemicals derived from coal, water, air, petroleum, agricultural by-products and natural gas.



            It was first developed by a research team headed by a U.S. chemist Wallace H. Carothers working in E.I. Dupant de Nemours & Co. He began experimenting with it in the 1920s. In 1935, he produced the first piece of nylon. It was converted into cloth in 1937.



            Nylon is made from two chemical compounds: Hexamethylenediamine and Adipic acid. Hexamethylenediamine consists of carbon, nitrogen and hydrogen. Adipic acid contains carbon, hydrogen and oxygen. Each of these substances contains six carbon atoms and the nylon produced by them has been named as Nylon-6, 6. Manufacturers combine the two compounds to form a substance called nylon salt. A solution of nylon salt is placed in an autoclave (a heating device). The autoclave heats the solution under pressure. Water is removed and the small molecules in the compound combine to form large molecules. This process is called polymerization.



            When caprolactam is used as the starting material, Nylon -6, 6 is obtained. It has been so named because it has six carbon atoms in the basic unit. It is comparatively a recent development.



            In some factories, the newly made nylon comes out of the machines as a plastic ribbon. This is then cooled, and cut into small pieces. Nylon fibres are made by forcing molten nylon through tiny holes in a device called spinneret. The thin streams of nylon that come out of the spinneret harden into filaments when they come in contact with air. Then they are wound into bobbins. From a single bobbin, as many as 2520 filaments are united into a textile nylon yarn. The fibres are drawn or stretched after they cool. The stretching action causes molecules in the fibre to fall into straight lines and make the fibres stronger and more elastic.



            Nylon can be formed into fibres, bristles, sheets, rods, tubes and coatings. It can also he rendered into powdered form for making moulds.



            Nylon fibres resist mildew and not harmed by most kinds of oil, grease and household cleaning fluids. It absorbs little water.



            Nylon is used to make many articles of clothing, parachutes, carpets, ropes, fishing lines and upholstery. It is also used in tyres and bristles in many types of brushes. Solid pieces of nylon are used to make bearings, gears and small machine parts. Unlike metal parts nylon bearings and machine parts need little lubrication.



            Recently a nylon derivative known as Qiana has been developed. It is a silk-like fibre used in clothing. Thus nylon has proved to be useful in many ways.  


How is electricity conducted through wires?


Electricity is supplied to our homes, schools, factories and stores through copper or aluminium wires from power stations. These power stations burn coal or oil, use nuclear reactions or the energy of falling water to produce energy to run the generators. The power thus generated is then transmitted to different cities and places where it is required. Electricity is then transmitted through transmission lines.



To avoid the loss of power, the output voltage from the generator is first stepped up to a high voltage by a step-up transformer. After being received at the city power station, it is again reduced to low voltage, before it reaches our homes or factories. Now question arises how is electricity conducted through wires?



We know that all substances are made up of atoms. Materials which allow the passage of electricity are called conductors. Metals, such as copper, aluminium, silver and gold are good conductors of electricity. The atoms of these metals have loosely bonded electrons. These electrons are free to move within the metal. These are called free electrons and are responsible for the conduction of current. More the number of free electrons in the metal, better it conducts the electricity. 





When electric battery is connected across the ends of the metal wire, the negatively charged free electrons move away from the end connected to the negative terminals and flow toward the positive terminal. This flow of electrons is nothing but the electric current. Hence the drifting electrons cause electricity to flow. Greater the number of free electrons in a metal, easier it is for electricity to flow through it.



Some materials are poor conductors of electricity because they have less number of free electrons. Poor conductors resist the flow of electricity. The resistance of a wire depends upon its material length and area of its cross-section.



Some substances do not allow electricity to flow through them and are called insulators. These substances contain tightly-bonded electrons that cannot move away from atoms. Hence they do not conduct electricity. Glass, mica, wood, plastic and rubber are common insulators. Some substances like silicon and germanium are neither good conductors nor insulators. They are called semi-conductors. 


How does an automobile engine work?

          An automobile such as a car is an automatic self-propelled vehicle. It runs on a gasoline, diesel or electric engine. Petrol or diesel engines used in automobiles are internal combustion engines. In these engines, fuel burns in the cylinder. In an electric engine, there is a motor and a gear box. It is battery-powered and used for small cars on a limited and experimental basis.



          Petrol engine is used in most automobiles. However, some automobiles even use diesel engines. Diesel engines are heavier and more expensive than gasoline engines, but they last longer and use less refined fuel.



         Both the petrol and diesel engines are four stroke engines. Their construction and working can be understood as follows:





Petrol Engine: It consists of a cylinder containing an air-tight piston. It is connected with the main shaft through a crank by means of a connecting rod. As the piston moves to and fro, its motion is converted into rotational motion of the crank shaft. The cylinder has two valves: one inlet valve and the other, exhaust or outlet valve. Inlet and outlet valves open and close automatically only once in every cycle. Air is mixed with petrol vapour in a carburetor and is made to pass into the cylinder through the inlet valve. The mixture is burnt in the upper portion by means of an electric spark provided by the spark plug. The action of the engine may be explained in four strokes.



          When the engine is made to work at the beginning by external force, the inlet valve opens and the mixture of petrol vapour and air is allowed into the cylinder. This is known as the charging stroke. Now both inlet and outlet valves close and the fuel mixture is compressed. This is known as compression stroke. The spark plug produces an electric spark and causes the mixture to burn. Due to combustion of the fuel, a large amount of heat is produced. This gives rise to heavy pressure and as a result the piston moves. With the movement of the piston the vehicle moves. This is known as the working or power stroke. Finally the exhaust valve opens, but the inlet valve remains closed. Unused gases, left at the end of the working stroke are thrown out. This is known as the exhaust stroke. In this way, one cycle is over. As the process is repeated, the vehicle goes on moving.



          Most automobile engines have four, six or eight cylinders. Most of the engines are in the front and drive the rear wheels. 


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How are hard drinks made?

          Wine is probably the first type of hard drink to have come into existence. Archaeological evidence suggests that wine making began in the middle-east over 10,000 years ago, and gradually spread westward to the mediterranean countries and finally into Europe. The ancient Egyptian wall paintings reveal that the art of wine making was known to them long before the Westerners took to it.



          Wine was common in everyday life of the early Greeks and Romans. It also played an important role in their religious ceremonies. The God of wine was called Bacchus by the Romans and Dionysus by the Greeks.



          Wine can be made from a wide range of fruits and vegetables, but the real wine is made from grapes. Grape juice contains water, sugar, fruit acids and many trace elements. The outer grape skin has millions of tiny living organisms, primarily yeasts, including a number of moulds and bacteria, too. 





          The grapes are allowed to ripen until they attain suitable sugar content (18% or more) and acidity. When these grapes are crushed, yeasts come into contact with the juice. This brings about the process of fermentation by which grape juice changes into alcohol and carbon dioxide. During fermentation, grape juice loses its sugar and turns into wine. This wine has 10 to 14% alcohol content. The rest of wine consists of water containing traces of acids, sugar and other substances which give the wine its colour and flavour.



          Another type of hard drink, beer, is known to have been made by the Egyptians and Babylonians at least 6000 years ago and there is evidence that barley, from which it is made, was cultivated in Britain and northern Europe, some 5000 years ago. Europeans knew how to produce a fermented drink from barley. Beer is usually made from barley hops, yeast and sugar by the process of fermentation.



          Pure brandy is made by the distillation of wine made from grape juice. The wine is heated and the alcohol that evaporates out of it is condensed and collected. Apart from alcohol, other substances are also given off during distillation. Some are poisonous substances and are removed.



          Different types of whisky are made from grains such as barley, rye and corn. Rum is made from molasses, syrup obtained from cane sugar. Gin is made from grain or molasses flavoured with juniper berries.



          Major wine-producing areas of the world include France, Germany, Spain, Portugal, Italy and California in the USA. 


How are matches made?

            When a strip of wood, cardboard or waxed paper tipped with a chemical mixture is rubbed against a rough surface, the chemicals burst into a flame and produce fire. The first match was made in 1827 by an English pharmacist John Walker. It was a splint of wood tipped with antimony sulphide, potassium chlorate, gum arabic and starch. The match bursts into flames with a series of small explosions that showered the experimenter with sparks. The first safety match was invented in 1844 by a Swedish chemist Gustave E. Pasch. Let us discuss how matches are made?

            Red phosphorous is the main substance used in the match industry. Matches are mainly of two types: Lucifer or friction matches and Safety matches. 





            Lucifer or friction matches light when rubbed against any rough surface. The match is basically a wood splint or shaft about 8 cm long and 0.3 cm in diameter. It may have a tip of two colours, red and white or blue and white. One-fourth of the wooden strip is first dipped in molten sulphur or paraffin wax. The small white tip is made from the paste of phosphorous trisulphide. Other substances are antimony trisulphide (kindling material), potassium chlorate (supporter of combustion), powder of glass or silica (friction producing substance) and gum or glue (to act as a binder). Red or blue part of the tip does not ignite by rubbing, but burns when the white tip has caught fire. It carries the flame to the rest of the match stick. These matches are made by machines which produce millions of matches per hour.



            Nowadays only safety matches are used. Safety matches can only be ignited by striking them against a special surface. The surface is usually located on the sides of the match box. The tip of the safety match is made from the substances mentioned above except phosphorous trisulphide. Red phosphorous is used as the igniter in place of phosphorous trisulphide. When the head of the match stick moves over the rough surface, the molecules in the head and the surface collide with each other and the head of the match becomes hotter. The substances in the head become hot enough and make the head burst into a flame. These matches generally do not light when struck on any other surface. The chances of such a match stick catching fire accidentally are thus eliminated.