Category Zoology

          Whenever somebody hiccups, it is often remarked that he is being remembered by some one. Some people even go to the extent of saying that the person who is hiccupping has secretly eaten something. In fact all these sayings are myths. It is just a reflex action of the body by which the body protects itself. The question arises: why do we hiccup?

          Hiccups are short, sharp, and very sudden breaths of air which happen when our breathing muscles jerks, making us gasp. There is a diaphragm located between the chest and the stomach. While inhaling air this diaphragm goes down and presses the stomach due to which the lungs are filled with air; while exhaling air, the diaphragm goes up and the air comes out from the lungs. Thus the diaphragm goes up and down and the process of respiration continues incessantly without making any sound. The diaphragm functions like a piston. But sometimes, due to the formation of gas or increase of acidity in the stomach, the diaphragm gets irritated and as a result contracts suddenly. In such a situation, the air passing into the lungs experiences obstruction and makes a peculiar sound. This is nothing but the hiccup. Therefore it is a process by which the body tries to expel gas or undesirable food material out of the stomach so that respiration remains unobstructed. Shrinking of the diaphragm due to drinking or the growth of a tumour near it also causes hiccup. Hiccups can be caused by eating or drinking too much or too fast. It may also be a symptom of mineral disorders and brain-stem disease.

          Hiccups usually last for a few minutes and disappear if nothing is done about them. The best way to stop hiccup is to drink a glass of cold water because the cold water stops the irritation produced in the diaphragm and it resumes its normal movement. Hiccup can also be stopped by holding breath for a while. Sometimes the hiccup stops when one sees something frightening. If the hiccup does not stop even after a long time, it is advisable to consult a physician. Generally under such situations, doctors prescribe the inhaling of oxygen mixed with 5 to 10 per cent carbon dioxide. Chlorpromazine also suppresses hiccup. 

          After a day’s work, we all get tired. Similarly we get tired after running, swimming or doing exercises. Do you know why we get tired after doing some work?

          When we do some work at a fast speed, our muscles do not get as much oxygen as they need. In such a situation to provide extra energy to the body, the glycogen stored in our muscles is transformed into lactic acid through the process of fermentation. The lactic acid reduces the working capacity of the muscles. This state of the body is known as muscle fatigue.

          The lactic acid acts as a poison for the muscles. If we can expel the lactic acid from the muscles by some process, they can again become fit for working.

          As a result of the muscular action some other substances called fatigue toxins are also produced in the body. Blood circulates these acids and toxins throughout the body because of which both the body and the brain get tired. Even when we do some mental work lactic acid and fatigue toxins are produced in the body and we get tired. Scientists have conducted many experiments in this field. A dog was made to work hard. And when it got tired and went to sleep its blood was transfused into an active dog’s body. This active dog also became tired and fell asleep. Similarly if the blood of an active dog is transfused to the body of a tired dog, it immediately becomes active.

          Fatigue is not only a chemical process but is a biological process too. It is a defence mechanism. This tells us as to when to stop work and give rest to the body. Fatigue cannot be removed fast. It is essential to give rest to the cells of the body to remove it. Sleep is a very effective means to remove fatigue. This repairs the damaged cells of the body. With the arrival of proper quantity of oxygen in the body through breathing, the lactic acid is reconverted into glycogen and we again start feeling fresh. Little rest also removes fatigue to some extent. The loss of glycogen due to fatigue is repleted to some extent by our food also. That is why a tired person feels very hungry.

          When we look at the human race we find that it is divided in two sexes – male and female. The question arises: Why don’t all people belong to one sex? What causes some babies to be girls and others, boys? In other words, what determines the sex of an individual?

          A woman becomes capable of bearing a child after she starts menstruation. Between the 10th and the 18th days from the onset of menstruation, the reproductive organs of a woman produce an egg called ‘ovum’. During this period if a woman mates with a man, a sperm present in the semen of the man fertilizes the egg. The combination of the ovum of the female and the sperm of the male results in the formation of the embryo in the womb.

          The ova of the female and the sperms of the male contain sex chromosomes. The ova have only one type of chromosome called X chromosomes. But the sperms have two types of sex chromosomes called X and Y chromosomes respectively. The X chromosomes are slightly bigger than the Y chromosomes in size.

          When female sex cells are to be formed, the two X chromosomes of the female germ cell come together. They then split lengthwise, forming four X chromosomes. In the formation of male sex cells, the single X chromosome pairs with its smaller partner, the Y chromosome. Each of these chromosomes split lengthwise. The cell then contains two X chromosomes and two Y chromosomes. When this cell gives rise to four new cells – the sex cells – half will contain X chromosomes, the other half, Y chromosomes. If these two kinds of sperm are equally efficient in reaching and fertilizing the egg cells, we should expect the two kinds of fertilized eggs to be equally numerous. Half of these would have two X chromosomes (XX) and would develop into girls. Half would carry one X and one Y chromosome (XY) and would give rise to boys. As a matter of fact, male births are slightly more frequent than female births. The reason is yet not known. 

          Of all the living beings only man can express himself in words. He is able to produce different types of sounds. Do you know how human beings produce sounds?

          Our throat has a hollow organ called the ‘sound box’ or ‘larynx’. It is, in fact, an enlarged part of the wind pipe. Its walls are made of cartilages and are lined with mucous membrane inside. The cartilage is made up of a very soft bony substance. The outer portion of our ears is also made up of this material. There are two vocal cords on the two sides of this box. Their movement is controlled by sixteen muscles. When air from the lungs passes through the vocal cords, they start vibrating. As a consequence of these vibrations, sound is produced.

          The sharpness, hoarseness and sweetness of sound depend upon the tension of the vocal cords. And this is controlled by the muscles. When the vocal cords are under higher tension, they can vibrate up to 1000 times per second, thus producing melodious sounds. In fact, more the number of their vibrations, sharper is the sound; and less the number of vibrations, the heavier is the sound. The rate of vibrations varies from person to person. That is why the pitch of sound is also different in different people. People with melodious voices have a better formed sound box as compared to others.

          When the child attains the age of 13-14 years, his vocal cords become thicker, as a result of which their frequency of vibrations is reduced. This lowers the pitch of the voice. Not only this, even our chest, stomach, tongue, lips, teeth, etc., are also involved in the production of sound. 

          It is a well-known fact that different kinds of sounds are detected by our ears. On the basis of its structure, the human ear can be divided into three parts: external, middle and internal. Anything producing sound first vibrates. These vibrations set up a motion of sound waves in the medium through which the sound reaches our ear. The external ear has large surface and can receive maximum number of sound waves.

          When the sound waves hit the external ear, they are transmitted to the middle ear through a pipe. The middle part has the eardrum which starts vibrating when these sound waves hit it. Just behind the eardrum there are three small bones called hammer, anvil and stirrup. As the eardrum vibrates, these bones also start vibrating. These vibrations are transmitted to the cochlea. The cochlea is the part of the inner ear which acts like a spring. It is surrounded by a fluid. The fluid has the nerve endings. Due to the vibrations of cochlea the fluid also starts vibrating and as such activates the nerve endings. The activation of the nerve endings produce impulses which are taken to the brain by the auditory nerve and we hear the sound.

          Our ears can detect both feeble and intense sound with frequencies ranging from 20 Hz to 20,000 Hz. In order to keep the ears healthy, it is essential to clean them regularly. A waxy substance is produced in it which gets deposited on the eardrum if it is not cleaned. If this wax accumulates there it can lead to deafness. Therefore, we should take care of our ears and consult the ENT experts as soon as there is trouble in the ears.

               Apart from human beings, cow, buffalo, sheep, goat, etc. come under the category of mammals. Mammals are those living beings whose females produce milk to suckle their young. They are warm-blooded and have well-developed brains. They give birth to live Youngs and feed them with their own milk. They breathe air through lungs and their bodies are covered with hair. Do you know how the female mammals produce milk? 

               Milk in the female mammals is produced by ‘mammary glands’ which are located in the breasts. They are bag shaped and big in size. Shortly before the birth of her young, hormonal changes in the mother results in increased development of the mammary glands. They produce large drops of fat which when mixed with fluids present in the breasts become milk. Corpus luteum of the ovary also produces a hormone which helps in the process of milk production. Most of female mammals have teats or nipples from which the young can suck milk.

               At present there are about 4400 living species of mammals grouped into 19 orders and about 120 families. They, of course, differ from one another in their bodies, shapes, sizes and habits. Most of them live on land but some live in water and air also. For example, the whale is a mammal which lives in water. And the bat is also a mammal which flies in the air. They exist in different climatic conditions – hot, cold, dry or humid. Most mammals give birth to less than 10 young a year. Humans usually have only one baby at a time.