Wisdom teeth are so called because they do not usually appear until the age of 18 to 20, by which time people were supposed to have become wiser. But surveys have shown that at least 19 per cent of the population of central Europe have failed to cut one or more wisdom teeth.
These teeth are the third molars and help in the process of grinding and chewing food. There should be four of them right at the back of the mouth next to eight other molars. Nearer the centre of the mouth are the eight bicuspids (or premolars) followed by the four cuspids (or canines) which are used for cutting and tearing food.
The eight front teeth, or incisors, are used mainly for biting and cutting, while the upper ones enable them to identify objects by nibbling.

Viruses are minute living organisms which consist of near naked nucleic acid (DNA). Once they gain entry into living cells, they become dangerous and capable of reproducing themselves. They cause many diseases, such as influenza, measles, poliomyelitis. In fact, once they have found a warm, moist place, rich in nutrients and biologically useful materials, viruses can create havoc ill the orderly running of the body.
Only the largest viruses can be seen with an ordinary microscope - an electron microscope is required to ‘see’ the majority. Individual viruses show a preference for certain tissues and locations in the body. Fortunately in most cases, one virus infection gives immunity for life. This is because the human body is able to identify· the harmful virus and manufacture a chemical, called an antibody, to attack and neutralize it. The snag is that some viruses, in particular cold viruses, remain one jump ahead and nobody has managed to find a cure.
Sometimes viruses need an ‘agent’, such as a bacterium, when they are taking over a cell. Some scientists have had the idea of suppressing’ the ‘agent’, the ‘bridge’ between the virus and the cells, by repeated vaccinations. Vaccination is a method of providing protection against illness by introducing diseased or dead germs into the body. The body is then forced to produce antibodies, which are harmful to microbes. The vaccination sometimes ‘smarts’, because the germs are inserted by a needle (given by injection).
There is no doubt that the battle against viruses is a very tough one, because they are rarely affected by medicines. It is amazing to think that during all the time that human beings have been suffering from colds in the head, no one has been able to find a cure!
Why do we have bones?
We have bones to give us shape and support the body, to protect and contain the body’s delicate vital organs, and to help us move about.
Bones are made from living tissue, composed of special cells which secrete around themselves hard material rich in calcium salts. Ina child the bones are soft and cartilaginous (Cartilage is gristle, the elastic substance of the ear or nose). Bone-making, or ossification, is a gradual process. A baby has as many as 270 bones, but an adult only 206, for some bones grow together as they get older.
All bones have a middle cavity filled with a yellow or red fatty substance called bone marrow, the blood-making factory of the body, which also keeps bones light without reducing their strength.
The basic part of the skeleton is the spine, which has 33 bones or vertebrae. The spine carries the weight of the body, is extremely flexible and contains, and protects the delicate spinal cord. The skull shelters the brain while the ribs protect the heart and lungs.
Bones fit together at the joints and are held firm by ligaments, which are made of tough tissue like cords or straps. Inside each joint is a thin membraneous bag which secretes a lubricant to make the joint move smoothly.
Some glide on one another, as the lower jaw slides on the upper. Some, such as the elbow and the knee, hinge on each other and others, like the hip, make a ball and socket joint. Bones are sometimes fused together and immovable, as in the five large, lower vertebrae called the sacrum.

Trees, like other living things, possess two essential elements: carbon and hydrogen. With the help of oxygen in the air, both these elements burn easily when set alight. In primitive times wood was man’s main source of light and heat. Fire was also used to scare wild animals away. People would set light to wood by rubbing two stones together to make a spark.
Now, although we have other sources of fuel, it is still very pleasant to sit by a log fire in the winter

During the day we use up a lot of energy which makes us tired at the end of the day. That is why we need to sleep at night. Whilst we are sleeping, the activity of every part of the body slows down and the whole body gets a deep rest. In fact, not only the body becomes rested, but also the mind. A good night's sleep gives us back energy so that we call work and play the next day.
Small children also need a rest during the day as they cannot store as much energy as adults. When we feel sleepy it means we need a rest.

Two thousand years ago, people did not know that rock and gas below the Earth’s surface caused volcanoes to erupt. They were afraid of mountains that rumbled and exploded mysteriously. They believed that angry gods made the mountains erupt to punish them.
The Romans called their god of fire Vulcan. They believed that deep inside Mount Etna, on the island of Sicily, Vulcan heaped coals on his blacksmith’s fire. This caused flames and sparks to leap up the chimney and through the mountain top. They though that Vulcan forged the lightning in a thunderstorm. People imagined him hammering and treating the hot metal when they heard distant thunder. The word volcano comes from the name Vulcan.

Saliva, the watery secretion Produced in our mouths, has many functions. It moistens the mouth and tongue, making sure that the mucous membrane does not dry or crack. It also moistens our food so that it can be moulded into an egg-shaped mass (or bolus) for swallowing, and it lubricates the bolus so that it can be swallowed easily.
By means of the enzyme ptyalin, which it contains, saliva begins the digestion of carbohydrates in side the food. Saliva also acts as a solvent to make tasting food easier, for the taste buds are stimulated only by dissolved substances.
It is a cleansing agent, washing away particles inside the mouth. If salivation is stopped, for instance in the case of a high fever, the mouth becomes dirty and tastes and smells foul. If salivation slows down, our mouths feel dry, and we know we need water. Salivia is secreted in the three pairs of salivary glands. The largest of these are the irregularly shaped parotid glands which are packed tightly into a space between the ear and the top of the jawbone. The ands are encased in an inelastic covering and that why, they are extremely painful if they swell. The next pair are the submandibular glands which are eggshaped and lie under the front of the jawbone, and the third pair, the almond-shaped sublingual glands, lie on the floor of the mouth between the tongue and the jawbone.

People stop growing when their bones do, and that is usually between 15 and 25 years of age.
Bones are made up of living tissue, composed of special cells which secrete round themselves material rich in calcium salts and as hard as marble. The formation of bone (ossification) is a complex process which usually begins in cartilage (gristle).
In a child the bone begins to form in the middle of the cartilage and spreads towards both ends”, turning it all to bone with the exception of the tips. From these points the bone grows in length and so does the child. When the growing period is over the tips of the bones close by joining the main shaft of the bone.
Bones vary greatly in shape and size. Long ones act as levers. Flat ones are centres for muscle action. But each has a cavity containing bone marrow.
Around this the bony substance is spongy in texture, becoming hard nearer the surface where the calcium is densest. On the surface of the bone is a special layer of fibrous tissue (the periosteum) which is rich in bone-building cells.

Hunger can be a pleasant or unpleasant feeling, depending on how strong it is and on the likelihood of it being satisfied. As with all other feelings, it is caused by external and internal stimulation.
Who among us has not found some room for that delicious cake? At the cinema, in the interval, tempting advertising shows us sweets and ice-cream with pictures to ‘make our mouths water’. There we are, caught in a carefully laid trap and we buy what is offered.
External stimulation by sight, smell or even sound (food advertising on the radio, for example) is added to internal needs. If the stomach empty, the body requests an intake of food. Contractions of the stomach containing only a little saliva and gastric sugar (produced by the stomach) can be painful.
When it comes to feeling hungry, habit counts for a great deal. Regular mealtimes are excellent for health, but they also impose their own slavery. If you generally have lunch at midday, it is normal to ‘have an appetite’ around that time. Very complex nerve mechanisms activate the digestive secretions and put us in a state ready to desire and receive food.
The hunger centre is situated in the brain under the cerebral hemispheres, behind where the optic nerves (from the eyes) cross. This is a very important region of the central nervous system called the hypothalamus. When some of these zones are stimulated, a feeling of intense hunger is created. Other zones, having the opposite effect, tell us when our hunger has been satisfied, or if we dislike certain foods. This centre receives information on our body’s needs. The information is then transmitted to other nerve centres responsible for carrying out the activities associated with feeding.
Internal and external stimulation, from memory or habit, can affect the hunger centre. This acts as a computer. It interprets the various types of stimulation and triggers the mechanisms necessary to satisfy the need for food, whether the need is real or imagined.