Category Zoology

            All mammals have some hair on their bodies and man is also a mammal. In some mammals hairs cover the whole body but in humans, hairs grow only in certain parts.

            Hairs on our body preserve the body warmth and protect the skin and body openings. They also help us in realizing the sensation of physical touch. The hair on our eyebrows and eye lashes, ear and nose help guard these body cavities against dust and insects.

            Now the question is, why do men have beards, and women do not? This can be understood as follows. When a child is born, he has only fur like hair on the body.

           As he grows, hair becomes harder. Boys and girls reach puberty at the age of 11 to 13 years. There is faster growth of sex glands at this age. In man, the testes and other sex glands, produce a group of hormones known as ‘androgens’. In woman, the ovaries and other sex glands, produce another group known as ‘estrogens’. The function of the androgens is to regulate secondary male sex features such as the growth of facial and chest hair and deepening of the male voice at puberty. The function of the estrogens is to regulate secondary female features, such as the change in the size of breasts, growth of pubic hair and onset of the menstrual cycle. There are various other changes in men and women brought about by these hormones. For example female body becomes soft and tender whereas, male body turns hard and strong. A special group of hormones called the ‘progestrogens’; are responsible for the regulation of pregnancy. Hence women do not have beards due to the absence of androgens.

            Man has five senses of perception – skin, ears, eyes, nose and tongue. The tongue tells us the taste of food and drink warns us if food has gone stale or is bad.

            The tongue is located inside the mouth and is an important muscle in our body. It is red in colour. If you examine it minutely, you will see granular bumps or projections on its upper surface, sides and back. These are called papillae. These papillae contain groups of contact called taste buds (chemoreceptors). They are composed of cells. Hairs like fibres emerge at the upper side of our tongue. At the lower end of the tongue, they end in nerve fibres of cells. These join the nerves of taste that lead to the brain.  

    The 4 main tastes are – sweet, salty, sour and bitter. All other tastes are a combination of two or more of these. These 4 main tastes are felt by different portions of our tongue. For example, salty and sweet tastes are felt by the tip of our tongue. Similarly, a sour taste is detected by the buds on the sides of the tongue and bitter taste, by the back portion of the tongue. The tongue is also sensitive to irritants such as pepper.

            The taste of food is known only when it is in the liquid state. As we chew our food, a portion of it dissolves in the saliva. This dissolved form of the food activates the particular taste buds. These generate nerve impulses and the nerve fibres carry these messages to the “taste centre” in the brain. The brain then perceives the taste.

            In addition to the tongue, our nose, which smells the food, also helps in perceiving the total taste of food. Smell is also a part of the taste. In the case of wine, cocoa and fruit juices, it is the smell which helps in the realization of the real taste. When liquids are taken into the mouth, the tongue experiences the taste while their smell enters the nose and through the “smell nerves”, it reaches the brain. In this way is derived the total pleasure of taste.

            When we suffer from cold, fever, or even constipation/indigestion, the taste buds get covered by some impurities and do not get properly activated. Heat of the body (in fever) or even hotness of food, also deactivates the taste buds. Hence, we do not perceive the real taste under such unhealthy conditions.

            The number of taste buds on the tongue of an adult is about 3000 which is much more than that of a child. As we grow older, the taste buds start losing vitality and, finally, become inactive, thus decreasing in number. In a 70-year-old man, for example, the number of taste buds is only 40. The taste buds, like all skin cells, are constantly being replaced. About half of the taste buds are replaced every ten days.

            Sleep is a bodily need that takes up about one third of life-span. After a whole day’s toil, both brain and body get tired. Sleep is necessary to restore energy and freshness to the tired organs and tissues of our body. It enables the body to repair worn out tissues and cells.

            Do you know how sleep comes to us and what happens to our body during sleep? According to scientific facts, there is a very complex area in the brain called “sleep centre”. Calcium ions present in the blood, control this centre. When an optimum quantity of calcium is received by the “sleep centre”, we get sleep. It has been observed from experiments on animals that they start sleeping when calcium is injected directly into the sleep centre. But if calcium is injected into the blood stream, this does not happen. During sleep, the sleep centre does two things. Firstly, it blocks off the brain so that we have no will-power or consciousness left and secondly, it blocks all nerves leading from the brain so that our internal organs and limbs fall asleep.

            In sleep, our body continues doing many types of movements. A man on an average changes his sides 20 to 40 times during sleep in one night. Blood circulation continues during sleep. Heart beat slows down a little bit. The digestive system works normally. Liver and kidneys perform their functions. The effects of sound, light, heat, smell etc. in sleep are the same on every sleeping person. During sleep, the body temperature is lowered by about one degree centigrade and the body cells are quietly engaged in getting rid of waste materials that have accumulated during the active part of the day.

How many hours a healthy person should sleep? The number of sleeping hours needed varies with individuals. The average adult needs from 7 to 9 hours of sleep. Boys and girls of 15 years of age need about 10 hours sleep each night. It is wise to form the habit of going to bed at the same time each night. Insomnia is the condition in which a person has difficulty in falling asleep. Such sleeplessness is often associated with pain, but worry can also keep a person awake. A dark, quite room that is well ventilated and cool is good for sound sleep. 

               We often see that people faint on hearing some sad news or on getting frightened suddenly. The bodies get drenched in sweat and become cold. Their faces turn pale. Physical consciousness diminishes. Unconsciousness can be caused not only by a shocking news or terrible fear, but by many other factors also. People may faint because of confinement in a close and poorly ventilated room, or because of hunger, fatigue, severe pain, emotional shock certain heart condition of sudden fall in blood sugar. Now the question arises: why do people become unconscious?

               In order to know the reasons of fainting, it is essential to know what consciousness is. For the normal functioning of the brain, it is essential that there should be proper circulation of blood in the brain. As long as the brain is in receipt of proper supply of blood, all our physical activities remain normal. The normal functioning of the brain is in fact consciousness. If there is some obstruction in the supply of blood to the brain, the common physical processes get disturbed. Whatever may be the cause of fainting, man will become unconscious when normal supply of blood to the brain is disrupted. Hence, fainting or syncope is a temporary loss of unconsciousness resulting due to the insufficient supply of blood to the brain.

               The state of unconsciousness can be prevented by some measures. If somebody feels that he is about to faint, he should immediately lie down. If that is not possible, he should bend downwards and enclose his head in between the knees. Both these measures enhance the blood supply to the brain and as soon as the brain starts receiving proper quantity of blood, the chances of one’s becoming unconscious reduce.

               If somebody has become unconscious, he should be laid down and his clothes should be loosened so that he can breathe easily. His head should be kept at a little lower level than rest of his body. This will increase the blood supply to his brain and he will regain consciousness. Once he is conscious, he should be given tea or coffee. If somebody has fainted because of head injury or heat stroke, he should be taken to the hospital immediately. 

           Generally most of the people are of normal height, but sometimes we come across people who are exceptionally tall or small. Persons who are exceptionally small are called dwarfs. In circus you must have seen such dwarfs who entertain you.

          Do you know why some people lack normal height? The growth of a person depends on many factors. Heredity plays an important role in determining the height of a man or a woman. Children of tall parents are generally tall while of dwarf parents are dwarf. In Africa, some tribes such as the Watusi and the Masai have many men who are about 200 cm tall. At the same time, there are Pygmy tribes in Africa, whose people are only about 130 cm tall. These variations are due to heredity only.

            Disease is also a reason causing dwarfness. There are cases of dwarfness in which head and trunk are normal in size, but arms and legs are short. This is caused by disease of cartilage. A normal body skeleton increases in length during childhood and adolescence because cartilage changes into bone at the growing ends of the bones. Disease of the cartilage prevents arms and legs from growing to a normal size.

            Dwarfness is often caused by the lack of hormones produced by pituitary gland. The underactive pituitary gland during childhood does not allow the body to grow normally. This type of dwarfness can be treated by injecting hormones. Too much or too little growth is also determined by some disorder in adrenal, pituitary, thyroid and male and female sex glands (testes and ovaries). The growth retardation may also be due to inadequate nutrition and intake of vitamins. The restoration of an inadequate diet, vitamins and mineral intake will also cause the child’s growth to spurt. A dwarf, named Jeffery Hudson, eighteen inches tall served as a captain of cavalry in the British Army. He lived from 1619 to 1692.

          Memory can be defined as the capacity to keep information available for later use. The process of memory can be divided in to the four aspects – learning, retention and forgetting, and retrieval. The initial storage of information is called learning, keeping the new information available is called retention, the loss of new information over a period of time is called forgetting and utilization of stored information is called retrieval.

            According to psychologists there are four kinds of learning. Classical conditioning is the simplest kind of learning. Ivan Pavlov studied it during the early 1900. He offered a dog food and at the same time rang a bell. The sight of food made the dog’s mouth water. Pavlov called this an unconditioned response because it was not learned. Soon, however, ringing the bell was enough to cause the dog’s mouth to water. This was called conditioned response. Classical conditioning is often called respondent learning.

            Another form of learning is called instrumental learning. Often a person learns to do something as a result of what happens after the person does it.

Multiple response learning is the third type and it takes place when a skill is learned. A sequence of simple things must first be learned. Using a typewriter is our kind of multiple-response learning. At first, a person has to type letter by letter. With practice, the person learns to type word by word or phrase by phrase.

            Fourth type of learning is insight learning. It means solving a problem through understanding how the different parts of a problem fit together. A simple example is that of a young child wanting to climb on the top of a table. The child may use a stool to get on to the chair and then use the chair to climb onto the table.

           There are two basic theories to explain the process how we memorise events. According to one theory, memory is said to be stored in the brain as a memory trace. When we learn or experience something, impulses are generated in the nerves of the brain. These impulses impart their effects in the brain in the form of a record. According to the other theory, sensations created by learning produce some permanent changes in the brain which remain there in the form of memory. According to some biologists, the R.N.A. (ribo-nucleic acid) present in the brain keeps the record of events. It has been observed that the quantity of R.N.A. present in the brain keeps on increasing from the age of three to the age of forty. During these years, the memory of the man also increases. The quantity of R.N.A. is almost constant from the age of 40 to 55 or 60. Therefore man’s memory is almost consent during this period. After the age of 60, the quantity of R.N.A. starts decreasing and so does the memory.

           The only effective way of remembering something is to repeat it many times Interest is very important. Boring things are much more difficult to remember than something that we understand and are interested in. Motivation or desire to do something is also important.