Coping with injury
Just look at your skin on the back of your hand. Touch it and squeeze it and see how soft and flexible it is. Skin is a very important and large part of the body. The surface area of the skin of an adult may be the same as that of an average tablecloth. The skin's flexibility lets it change shape easily as you move. It has tiny organs in it which are sensitive to touch, it produces sweat to cool you down when you are exercising and replaces itself quickly as it is worn away, but there is just one weakness. It can be easily damaged. Just think about the cuts and bruises you have had. You may have some now. Fortunately, when the skin is damaged, the body swings into action to repair the injury.
During the course of the day some sweat emerges from inside your skin and spreads across its surface. Water in the sweat may evaporate but oils remain behind. These oils form a food for bacteria that land on the skin. If you do not wash regularly the bacteria can build up large numbers. The bacteria cannot get through the surface of the skin but when the skin is cut they teem onto the exposed flesh and can cause harm.

The body, then, is faced with two problems when the skin is cut. The bacteria have to be removed and the wound has to be healed. The first way in which the body tries to remove bacteria is by simply flushing them out with blood. At the site of the cut the blood vessels open and blood pours out to wash the bacteria away. However, the body cannot use this method for long, as there is only a certain amount of blood that can be safely lost. As the blood is flowing from the wound, large numbers of white blood cells are making their way to the damaged area. White cells have the ability to change their shape. When they arrive at the wound, each white cell attacks a bacterium by forming fingers around it. The fingers come together just as the fingers in your hand may come together and they fold over the bacterium just as your fingers may fold over a small object such as a sweet or a peanut. When the white cell has taken the bacterium into its body, it kills and digests it. During this process the white cell dies. You cannot see this happening but after a while you may see white matter called pus develop in your cut. This is made from thousands of bodies of dead white cells.

While the white cells battle with the bacteria, another component in the blood works at stopping the flow of blood. These structures are called platelets. They are much smaller than cells. There are about a quarter of a million platelets in a drop of blood just one millimetre across. The blood contains many chemicals but the platelets work on just one. They turn this chemical into microscopic fibres. Huge numbers of fibres are produced and they mesh together to stop the blood escaping.

Once the bleeding has stopped, food is brought to the wound by the blood and is used to make new cells. While the new cells are forming in the flesh, a scab forms on the skin's surface. Its job is to keep out bacteria until the new skin surface has been made. In time, if the wound is small, the scab will fall away and there will be no sign of the damage that was done earlier.

Do all animals have soft skin?
No. Some animals like insects, woodlice, crabs and lobsters have a hard skin, which forms a skeleton on the outside of the body. These suits of armour are not flexible. However, there are thinner flexible parts to the skin in the joints in the legs, which allow all the animals to walk, and the insects to fly. The armadillo is a mammal which has a hard skin on its back, but has joints in it which allow the animal to roll up into a ball. The elephant and rhinoceros have thick, tough skins, which are also flexible.

What happens to the bacteria if you do not wash your skin?
They remain on your skin. They feed and breed and produce wastes, which makes your skin smell. This smell is called body odour or BO. The main danger is if you damage your skin. They can then reach your flesh and cause harm.

How can the bacteria cause harm?
Some may feed on the exposed flesh and their poisons may enter the blood. Other bacteria may be disease-causing bacteria. If they enter the body, they may make the body ill.

If you wash your skin regularly, and always wash you hands after visiting the toilet, you reduce the chance of bacteria invading the body through a wound.

How much blood is there in the body?
The body of an adult has between five and six litres of blood. The blood cells are made in many bones in the skeleton.

Are there more platelets in the blood than red blood cells?
No. There are about five million red blood cells in a drop of blood one millimetre across. Normally there are only about ten thousand white blood cells in a drop of blood one millimetre across but the body makes more white cells when it is under attack from bacteria.

Why is losing too much blood dangerous?
Blood contains everything the body needs to keep it alive. It contains food, oxygen and it carries away waste. Without blood, cells die quickly. The heart also needs to have a certain volume of blood to pump to keep its muscles working. If there is not enough blood the heart stops.

When an injured person is running short of blood, can anybody's blood be used to replace it?
No. There are four main types of blood. When a person needs more blood, a sample of their blood is tested to find its blood group. Blood that matches the patient's blood is then taken from a blood bank and it is put into the person's body in a process called a blood transfusion.

Why do some wounds need stitches?
The wounds are too large to close on their own. So the separated pieces of flesh are sewn together by threads. This helps to keep out bacteria and aids the body to make new cells to heal the wound.

Could Stone Age people have stitched up large wounds?
They may have been able to do this. In the recent past some people living in Australia and Africa used to stitch wounds using thorns for needles and vines for threads. Stone Age people may have used the same materials.