Staying healthy
With billions of microbes floating in the air around us, covering every surface of our world, you may think that it is amazing that any other forms of life can exist. It is important to remember that most microbes are not harmful. It is equally important to remember that some of those microbes, which are harmful, can be deadly. We can survive among them because our bodies do have some defences against them.

Imagine you are a harmful microbe that needs to invade the body to feed and breed. Microbes cannot buzz about like flies but for the purpose of these ideas imagine that you are a microbe and you could. First you would land on the skin. It is covered in a thin layer of oily liquid called sweat, which contains some natural antiseptics, which could kill you. If you found a patch of skin without sweat you would find your way blocked to the inside by a layer of dead skin cells, which looked like flags in a pavement. You could not get past them. It is time to attack the head.

The only surface on the head that is not covered with skin is the surface of the eyes. This seems a good place to attack but when you get there you find that the surface is washed by a thin film of water. This is produced by glands under the upper eyelids and is spread across the eye when we blink just like windscreen wipers spread screenwash on the windscreen of a car. In this liquid is an enzyme, which attacks many bacteria and makes them dissolve. The eye is not a place to gain an entrance to the body.

The nose looks a more promising place to invade the body so you drift into it when a person inhales. As long as you can keep away from the sides of the nose as you go into the head you are safe. If you touch the sides you are trapped in mucus and attacked by the same enzyme that was on the eyes. If you enter by the mouth this enzyme is in the saliva too.

If you can pass through the nose and move down the centre of the windpipe you can get into the lungs and set up an attack on the body. If you touch the sides of the windpipe you are trapped in mucus but then something odd happens. You are bundled up the windpipe in the mucus. This movement is brought about by tiny hairs, which line the wall of the windpipe beneath the mucus. They beat backwards and forwards like oars in a rowing boat and push the mucus up the windpipe. If you have been inhaled by a smoker you will be in luck. The smoke will have killed these cells so you will slide down into the lungs to join in the damage that is already occurring there. If you are unlucky and are inhaled by a non-smoker you will reach the top of the windpipe and be swallowed down the gullet. This is the tube which takes the food from the mouth to the stomach. When you reach the stomach you are plunged into a liquid, which contains strong acid, and are killed.

Imagine that you have been partly successful in invading the body and have found a place to feed and breed. Your problems are far from over. If you have settled in the nose the person may start sneezing to blow you out. If you have settled deeper in the breathing system the person may cough strongly to dislodge you and send you out on drops of mucus. Some harmful bacteria manage to survive on the skin but will only thrive if they can get inside the body. If the skin is cut they have their chance to enter the body but there is another defence mechanism in their way. Blood pours out of the cut to swill away harmful microbes then it clots to seal the wound and prevent them getting in.

Despite the defence mechanisms they have met some microbes still manage to get into the blood and cause disease but the body has yet more ways to stop them. Viruses enter cells and use the materials there to breed. The cells produce a substance called interferon, which does as its name suggests - it interferes with the virus attack and stops them breeding. Both viruses and bacteria come under attack from white blood cells. These cells roam the blood and eat any microbes they find. However if the microbes are breeding fast the white cells can soon be outnumbered. When this happens, the body throws its last line of defence at the microbes. It makes antibodies. These are substances which weaken the microbe and stop them breeding. They may even stick them together and make them easier for white cells to eat. Once the microbes have been destroyed by the antibodies the body may be immune to further attacks for a long time - even for life.

As you can see, the body has many ways of fighting off an attack by harmful microbes. You could do your body a favour by adopting a healthy life style and eating a nutritious diet, taking exercise and refraining from smoking. If you do this, harmful microbes will find it very tough trying to get through your defences.

Can microbes move about?
Some microbes can. They have a few long hairs or many tiny ones, which they wave about in the liquid around them to swim. A few have soft walls to their bodies, which allow them to bulge out and flow along. Microbes in the air are in the form of spores. They cannot move on their own. They are just carried along with the air currents and it is pure chance where they land. This is why so many of them are produced. If only a small number were produced they might all land in unsuitable places. If a large number is produced there is a chance that some of them will find a suitable place to feed and breed.

How does washing hands before eating help us stay healthy?
During the course of the day you handle many things. All of them are covered by microbes. Some of the microbes could be harmful. When you wash your hands, an antiseptic in the soap kills the microbes so they cannot harm you. If you do not wash your hands, there is a chance that the harmful microbes may get onto your food and pass into your digestive system. If there are a large number of harmful microbes entering the stomach with the food, not all of them are killed by the acid and some get through into the intestines. If you wash your hands, you reduce the numbers of harmful microbes that could enter the stomach with your food and give the stomach acid a better chance of killing them all.

Why should you wash your hands after going to the toilet?
The solid wastes that you produce at the toilet are called faeces. They are teeming with bacteria. It has been found that a piece of faeces about the size of a lentil contains ten billion bacteria. This means that when you go to the toilet there is a chance that some microbes may reach the skin on your hands. Many of the microbes that live in your intestine do no harm there. If they were to reach other parts of your body they could cause diseases which could be fatal. If you do not wash your hands you increase the chance of spreading the harmful bacteria onto other objects which other people may touch. If you have a meal there is a chance some of the harmful bacteria on your hands may enter your body with food.

How do low temperatures control microbes?
Low temperatures do not kill microbes, they slow down the rate at which they breed. In a fridge the low temperature slows down the speed at which the microbes breed on the food or in drinks so that they may be safely kept there for a few days. In a freezer the temperature is so low that breeding stops. As soon as the food is thawed out breeding starts again.

How do high temperatures control microbes?
They kill them. The purpose of cooking food is to make it more digestible but it also kills microbes in the food. However, if cooked food is left for some time, more microbes will settle on it and start to breed so cooked food must not be left too long before it is eaten. Pasteurisation is a process in which drinks such as milk are heated to a high temperature for a short time to kill the microbes in them. However, spores are not killed by this process and in a few days microbes emerge from them and make the milk go bad.