My Science School

Bats use high-pitched sounds to find their way about. They are nocturnal animals. That is they move about by night. So they have developed their hearing to such an extent that they can find their way by a method known as echolocation.

     The blind-flying abilities of bats were first studied by LazzaroSpallanzani (1729-1799). He surgically removed the eyeballs from several bats to prove that they did not need to see to fly.

    In the 20th century, biologists, using electronic instruments, have carried out experiments with bats. They have discovered that bats find out where to go by emitting high-frequency sounds and receiving the echoes as they bounce off objects. Most of the sounds have too high a frequency to be heard by the human ear.

    Bats commonly fly together in groups, but apparently they are not confused by he sounds and echoes produced by each other. When hunting in woods and in the rain they are able to discriminate between the faint echoes bouncing off the ground, tree-trunks, branches, twigs and raindrops.

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Cardiac pacemakers are used by sufferers from “heart-block”. They do the work normally performed by the body’s natural pacemaker in controlling the rate and rhythm of the heart beats. This natural pacemaker is a small collection of specialized nervous tissue situated at the base of the heart. It forms the starting point for the impulses that initiate the heartbeats.

    “Heart-block” is a serious condition in which the conducting mechanism between the cavities of the heart (atrium and ventricle) is impaired or destroyed. When this happens, the atrium and ventricle beat at different rates independently of each other because the impulse from the pacemaker is not reaching all parts of the heart. Fainting, convulsive attacks or complete stoppage of the heart may follow, but the condition can be overcome by the use of an artificial pacemaker.

      This acts as a battery to stimulate the heart, allowing it to beat regularly at normal speed, about 70-80 impulses a minute. The pacemaker is either fixed to the outside of the chest or implanted in the armpit and connected to an electrode tube, which is passed through the main vein in the neck into the heart.

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Muscles are the body tissue which, because it has the power of contraction, enables the higher animals to move their bodies. Muscles are divided into two great groups, voluntary and involuntary, the former being controlled by the will, while the latter act independently

     Most voluntary muscles are attached to the skeleton and range in size and shape to suit the particular jobs they perform. They can get into action within a few hundredths of a second, exert an enormous pull on the bone to which they are attached and, if necessary, support 1,000 times their own weight. Involuntary muscles include heart muscle and the muscles of the digestive system, and the fibers of which they are composed are very much smaller than those of voluntary muscle.

    Because of its exceptionally rich blood supply, muscle is the most infection-free of the body’s basic tissues. If it is over-taxed it tires and will stop contracting altogether, but if used normally will give little trouble.

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Some scientists consider that sleep is an instinct, a basic need for the body and mind to relax and to escape from the responses needed while awake. We become tired in body and mind if we do not sleep, and scientists have proved that when we do sleep the electrical activity of the brain slows down, although it may be stimulated when we dream.

     One chemical theory is that a substance needed to maintain the waking state becomes exhausted and may be replenished in sleep. A contrary suggestion is that some poisonous substances built up in wakefulness may be destroyed when we go to sleep.

   Other theories connect the need for increased wakefulness with the development of the more sophisticated areas of the brain. This could explain why new-born babies whose powers of reasoning have not yet developed, spend most of their lives asleep. It has been demonstrated that a particular formation, if severed, causes continues sleep.

     Although we are not sure why we sleep, there is no doubt that we need to do so and so do most other animals. The pattern of sleep and wakefulness is closely connected with our habits and senses. Animals which depend upon sight for food, shelter and defense, like man, are diurnal. That means they are for the most part active during the day and asleep at night.

    The amount of sleep needed by a person to remain in full health varies considerably with age, with different individuals, and even, perhaps, with race. Pre-school children generally need ten to twelve hours sleep schoolchildren nine to eleven hours and adults seven to nine hours. Adults seem to need progressively less sleep as they grow older, and exceptional cases are known of elderly people who have remained healthy on two to three hours a night. It has been said that the Japanese, children and adults, sleep less than Europeans, but that may be due to habit rather than to race.

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We take a grip on things by using our muscles to exploit the development of the human thumb. The importance of this thumb is that it can be moved across the palm of the hand to touch the index finger. In contrast the digits of a monkey’s hand are more rigid. This difference explains why a human being can handle an instrument with such precision.

     The mechanism of the hand is operated by way of the wrist, a hinge joint composed of eight small bones (carpals) packed firmly together to give elastic stability. Below the wrist project five small, long bones (metacarpals) which give the palm firmness. Four of the bones have hinge joints and are connected to the thumb allows it to move round and meet the fingers and palm, thus providing a firm grip.

    Possession of such a hand has enabled man to form a society and culture based on the use of tools. It is thought the hand developed from the five-rayed forepaw of an early vertebrate. However, occasionally a child is born with an extra tiny thumb or little finger and some people believe that the forepaw was originally seven-rayed.

    The human thumb has length longer in proportion than that of an ape. About 92% of human being is right handed, but apes tend to use both hands with equal ease.

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Inside the womb of a pregnant woman or animal a placenta is formed, through which the unborn baby is nourished. The baby is connected to the placenta by the umbilical cord, which is joined to the unborn child at the navel.

     The umbilical cord is the baby’s lifeline. Everything the child needs to survive will pass through it- air, blood and nourishment. At most it is no more than an inch wide and, perhaps, only a foot long.

    Once the baby is born the placenta, which serves a purpose only during the pregnancy, will be discarded.

      The umbilical cord will be cut with scissors a few inches away from the newborn baby’s stomach. This is quite painless because the umbilical cord has no nerves. The baby will now breathe on its own.

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The most likely places to catch malaria would be in tropical and sub-tropical countries, especially in the forested parts of Central Africa, Asia, and southern Europe. This is because the female anopheles mosquito, whose bite transmits the diseases, breeds in the warm, stagnant, marshy pools found in those parts.

    Malaria is said to derive its name from the Italian for “evil air”. It causes chills, fever and anaemia, and is sometimes fatal. In India a million people are likely to die from it every year.

     The first effective remedy for it, quinine, was used in the 16th Century. It is an infusion from the bark of the cinchona tree. Modern drugs, too, have greatly reduced the threat of malaria. In particular the use of sprays on the mosquitoes breeding places has been highly effective.

    In 1955 the world Health Organization started a mosquito-eradication programme of benefit to nearly 1,200 million people.

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Dizziness most commonly occurs when a person who has been moving around with speed stops suddenly. The sensitive liquid in the inner ear, which mainly controls balance, continues to move around for a time after the body has stopped. So the surroundings appear to be still in motion. However, it takes only a few seconds, for the fluid, and balance, to settle.

    This sensation, which is also called vertigo, may also occur to someone looking down from a height or on board ship. Here the cause is probably not so much physical as a nervous reaction which affects the fluid in the inner ear.

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The body temperature of a human being is an indication of his physical condition, so that an abnormally high or low temperature is generally a sign that something is wrong.

     The normal temperature is usually given as 36.90 C. (98.40 F.), but as the body temperature varies throughout the day, anything between approximately 36.70 C. (OR 98.10 f.) and 37.20 C. (or 99.00 F.) may be taken as normal.

    For instance, the temperature rises after a large meal, during hot weather and after violent exercise. Your temperature is at its lowest at night when you are asleep.

    Control of body temperature is exercised by a centre in the brain which ensures that a balance exists between heat production and heat loss. A raised temperature is often the sign of bacterial or virus infection. It may be due to heatstroke, to certain types of brain injury or disease or to shock.

     A very high temperature, or fever, may begin with a “rigor” (an attack of shivering and cold), in which the whole body may tremble uncontrollably and the teeth chatter. Although at this stage the skin feels cold and clammy, the temperature within the body is raised. Soon the skin becomes hot and dry, pulse and breathing rate are speeded up and there is a feeling of exhaustion, aching muscles. Headache, thirst and perhaps delirium and loss of the sense of time.

    Finally this stage is succeeded by profuse sweating and a gradual relief of the symptoms.

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Blood congeals when a part of the body is wounded. If it failed to congeal the injured person would die from loss of blood.

    The congealing, or coagulation of the blood, is the first step towards healing a wound. It closes the wound and builds a scaffold for new tissue by means of a chemical process in the plasma, the fluid part of the blood. In this process the platelets (small cellular bodies in the blood) produce thromboplastin. This changes fibronigin, a protein in the blood, into fibrin. Finally a spongy network of fibrin connects the edge of the wound and prevents the loss of any more blood cells. Often, a scab is formed over the wound as a protection.

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We become sea-sick because our balancing organs, the labyrinthine portions of the inner ear, are disturbed by out-of-level movements, by sudden turning movements, or by sudden changes in movements in a straight line, either horizontal or vertical.

       The ear has three semicircular canals, filled with fluid and set on different planes in the ear. When sudden movements occur, each canal is affected differently. As a result, nerves in the canals send conflicting information to the brain, so giddiness is likely to occur.

        Nowadays, seasickness comes under the general heading of motion sickness a name invented by Sir Frederick Banting in 1939, which include the discomfort people feel while travelling in all kinds of vehicles.

    Sea-sickness may vary with individuals from slight uneasiness to complete prostration. The symptoms are pallor, cold sweating, nausea and vomiting. People who have lost their ear labyrinths because of disease do not become seasick. Others become resistant to it. We say they develop their “sea-legs”, but it would appear to be an adjustment of the central nervous system rather than the organs of balance. Some people find it helpful to keep their gaze firmly fixed on a steady object.

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The brain directs and coordinates movements and reflexes, registers sensations and is the supreme nervous organ by which man acquire knowledge and the power to use and adapt it. It shapes our personalities, and without it we would be more helpless than the tiniest human baby.

       There are three main parts of the brain: the forebrain (or cerebrum), the midbrain and the hindbrain. They have the consistency of soft jelly and are protected by three membranes (meanings), a tough outer envelope called the dura and a water fluid (cerebrospinal fluid) which acts as a support and a cushion. The brain is connected to the spinal cord, and its surface is highly convoluted.

      The cerebrum which forms nearly nine-tenths of the brain is divided into two halves (hemispheres). Generally the left half of the cerebrum controls the right half of the body, and the right half of the cerebrum controls the left half of the body. Some areas are connected with the special senses of man, but there are so-called “silent areas” which scientists believe are connected with memory and the association of ideas. The thalamus, a mass of grey matter which is buried in the cerebrum, is the source of instinctive feelings and emotion.

    The midbrain is concerned with eye-movements, while the hind-brain contains the nerve cells responsible for breathing, heart action, and digestive juices and so on. The cerebellum, a part of the hindbrain, plays an important role in the execution of the more highly skilled movements.

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The night vision of Owls is 100 times as keen as that of human beings, because their eyes are especially adapted for seeing in the dark. But most are almost colorblind and the pictures they receive are slightly blurred. This is because their eyes contain more rod-shaped receptor cells than cone-shaped ones.

        Operating in bright light, cone cells sharpen details and react to colour. Rod cells gather light and owls have 10times as many of these as do human beings. Each cell contains “visual purple”, a substance capable of transforming the slightest glimmer of light into a sight impression.

   Owls have exceptionally large eyes and can control the amount of light entering by expanding or contracting the pupil. Each pupil can act independently of the other so that owls can see objects in the shadows and in bright light at the same time. Owls’ eyes are so large that they are supported by thin, bony, and tubular structures called sclerotic rings. Because of this the eyes are almost immovable and nature has compensated for this by giving owls extremely flexible necks, which enable them to turn their heads through an arc of 270 degrees.

     These birds have excellent binocular vision as their eyes are in the front of their heads. This gives them a tremendous advantage in swooping on small lively prey, because distance judgment depends on binocular vision. To add to their advantages at night, the owls have outstanding hearing, keener than that of any other carnivorous bird.

    But owls can also see well in the daytime. Although most species hunt by night, others are active at dusk or in full daylight.

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