Recovering from disease
Look away from these words to a pace across the room. You may see a chair or table there, or a poster on the wall. You may think that there is nothing in the air between you but you would be wrong. Have you ever been in a darkened room with a shaft of sunlight shining through a gap in the curtains? If you have, you will have seen specks of dust and even small hairs glinting in the light and seeming to dance in the air. These tiny objects are present in air everywhere but it is only in special conditions of the light when they can be seen.

However, there are objects in the air which are smaller still. They are so small that they are measured in units called micrometres. Look at the distance of a millimetre on your ruler then imagine that space divided into a thousand parts. Just one of those parts is a micrometre long. These objects like microscopic grains of rice are called bacteria. They rise up and down in the currents in the air and settle on every surface they can. Bacteria are found almost everywhere from the top of the atmosphere to the depths of the oceans. Most are harmless but some can cause disease and even kill.

Bacteria are living things. The bacterial objects in the air are called spores. Each one is a case with a bacterium inside. The walls of the case are thick and tough. This protects the bacterium from heat and cold and prevents it losing water as it floats in the air. As you read this you are inhaling air containing bacterial spores. If you are healthy, your body defences will prevent them attacking and the spores will be blown out again when you exhale.

Imagine what would happen if you were not healthy and you inhaled some harmful bacterial spores. They could settle on a surface inside your body and break open. When a bacterium breaks out of its spore it feeds on the substances around it. It uses the substances to grow and in the warm conditions inside your body it grows rapidly. When a bacterium is fully grown it breeds. This is a simple process. The bacterium divides into two. In ideal conditions a bacterium can grow and breed every twenty minutes. This means that twenty minutes after a bacterium broke out of its spore there will be two. In another twenty minutes there will be four and by the time an hour has passed there will be eight.

You do not usually pick up one harmful bacterial spore: you pick up thousands. They may be in the air just after someone has sneezed, they may be coating the handle of a toilet or covering a piece of food which has had flies walking on it. This means that you would not have eight harmful bacteria in your body after an hour but perhaps eight thousand or more. If conditions in your body were ideal for the bacteria, their number would become sixteen thousand in the next twenty minutes and by the end of the second hour there would be at least sixty four thousand harmful bacteria feeding inside you.

As the bacteria feed they produce wastes just like other living things. The wastes of the harmful bacteria are poisonous to the body. When the numbers of the bacteria reach a certain size they are producing so much poison that they make you feel ill and the disease takes hold.

You may think that the bacteria go on feeding and breeding indefinitely inside your body until your body is teeming; with them but this is not the case. Firstly, it is unlikely that conditions will be ideal for the bacteria and this means that they feed and breed more slowly so the speed of their invasion is much slower. Secondly, the body has a defence system which attacks the bacteria and destroys them. It takes the body a little time to form its defences after an attack but once the system is in place the number of bacteria decrease, the amount of poison is reduced and you begin to feel better.

What kind of body does a bacterium have?
It is similar in many ways to a cell in your body. There are three kinds of body shapes. Some bacteria have spherical bodies. They are called cocci. Some of these bacteria form groups. Two groups that you may sometimes hear a doctor or nurse mention are staphylococci and streptococci. Staphylococci form a group like a bunch of grapes and streptococci form a group like a chain of beads. The second group of bacteria have rod-shaped bodies which are called bacilli. The third group of bacteria have rod-shaped bodies, which are twisted into a corkscrew shape. There are two kinds of bacteria with this shape called spirilla and vibrios.

What kinds of diseases are caused by bacteria?
Tetanus, tuberculosis, typhoid, cholera and diphtheria are a few examples. Bacteria can also cause boils.

What is an antibiotic?
It is a medicine, which can be taken to kill bacteria. Penicillin is a widely used antibiotic but there are many more. Antibiotics do not work against viruses.

Are viruses like bacteria?
No. They are about a thousand times smaller than bacteria and they do not have a body similar to a cell. There are really just two parts to a virus ? its case and a chemical it uses to breed or reproduce. There are many different shapes of virus but they all have the same simple structure. You can find many different kinds of bacteria living in different habitats. They feed on dead plants and animals. Viruses do not do this. They only appear to come to life when they have attacked a living body. The rest of the time they appear lifeless. They can even be stored in a jar like crystals of sugar.

How do viruses attack the body?
They go straight into the cells. Once inside the cell each case breaks open and its breeding chemical makes copies of itself. Cases then form around each copy and a new virus is formed. The virus uses materials inside the cell to make copies. This damages or destroys the cells and causes the disease.

What kinds of disease are caused by viruses?
Chickenpox, measles, polio and rabies are just a few diseases caused by viruses. Viruses also cause warts.

Can the body be helped to defend itself from viruses and harmful bacteria?
Yes, it can. Vaccines have been developed to help the body build up its defences before it is attacked. A vaccine contains dead or weakened microbes. They do not harm the body but let the body recognise them and prepare defences. If the body is later invaded by the disease causing microbes it can defend itself quickly and kill them so the disease does not develop. Vaccination is also called immunisation. In the United Kingdom children are immunised against diphtheria, tetanus, whooping cough, polio, measles, mumps, rubella and tuberculosis.