Microbes and your body
For about the last five hundred years people have been exploring the Earth. They have sailed across oceans and up rivers. They have crossed lakes, climbed mountains and hacked their way through jungles. Some have survived crossing deserts and the snowy wastes at the North and South Pole. On these expeditions the travellers have made a note of the plants and animals they have seen and even brought back specimens. What would it be like to explore the surface of the body as if making expeditions across the world?

Imagine that you could be shrunk down to the size of a microbe and be put on someone's skin. How would your travels be different from those of a traveller across the Earth? A major difference would be that wherever you travelled over the skin things would be pretty much the same. There are no pools on the skin that you could describe as oceans or lakes; there is no running water like that in rivers and streams. There are no different substances such as sandstone or limestone on the Earth. Everywhere is covered in the same material - a protein called keratin.

As you looked out across the protein landscape, you would see holes in the surface. At times an oily liquid, which tasted of salt, would well up in them and flow out over the surface. This liquid is sweat. Spread out over the surface would be other holes. From each one would rise a structure which looked like a very tall tree trunk without branches. This structure is a hair. The atmosphere above the skin would be much the same wherever you went but it would be damper above the skin between the toes and under the hair on your head.

On the Earth there is a huge number of different habitats which provide homes for millions of different kinds of living things. On the skin there is mainly one habitat with slight changes where the air above the skin is damper. As you looked out across an area of skin, say on the arm or leg, you would see ball-shaped bacteria clustered together like a bunches of grapes. Among them would be some bacteria which form groups of eight and are shaped like cubes. There would be smaller, ball-shaped bacteria too and some yeasts. If you ventured onto the skin between the toes or in the armpit you would find rod-shaped bacteria and more yeasts. On the skin of the head are many yeasts. Some may have settled there from the air as the air carries many yeast spores.

You may also find bacteria on the skin which could cause the body harm but their numbers are kept in check by other bacteria. These produce chemicals which attack the harmful bacteria and prevent them breeding. Sometimes one kind of harmful bacteria may get its chance to breed quickly and when it does it causes a boil to develop. If the skin is cut then harmful bacteria may enter the blood and cause disease before the body's defences can overcome them. You can help protect your body from these invaders by washing your skin regularly to keep it clean.

If you just look now at the skin on the back of your hand, think about the kind of world it is down there in the land of the microbes and remember that you are not alone. There are millions of tiny living things depending on you for their survival, just as we depend upon the Earth for our survival.

What is athlete's foot?
It is a fungus that grows on very moist skin. If you do not dry between your toes after washing your feet you stand a good chance of the athlete's foot attacking your skin. It produces a chemical which digests your skin, then draws the digested skin into its body. This leaves the skin red, raw and painful.

Can athlete's foot be cured?
Yes. You can use a foot powder which contains a fungicide. This is a poison that kills the athlete's foot fungus.

Are microbes found in the mouth?
Yes. Bacteria coat the inside of the mouth in a similar way to the way they coat the skin. Bacteria also live on the surface of the teeth.

Are the bacteria in the mouth harmful?
Those on the lining of the mouth are not harmful but those that live on the teeth can cause tooth decay. These bacteria feed on sugar. When they feed the bacteria make acid which attacks the surface of the teeth. In time, if the teeth are not regularly cleaned, the acids may destroy part of the white coating of the tooth and cause the inside to decay.

Do microbes live inside the body?
Yes. A range of microbes is found in the intestines. There is a certain number of each kind and they form a balanced population which is harmless. Sometimes the balance of the population of microbes may be upset. When this happens you may get pain in your intestines, which you call stomach ache.

What can cause the balance of microbe population to be upset?
When you go to another country on holiday the unaccustomed food and drink you take in there may cause the balance to be upset for a few days until it settles down again.

Can you take in harmful microbes with food and drink?
Yes, you can. Some of them can cause very serious diseases and
even death. Fortunately there are only a few kinds of really harmful microbes like these.

Does the body have any defence against the microbes it takes in on food and in drinks?
Yes, it does. The stomach produces an acid. When the microbes enter the acid they are destroyed. However if a large number of harmful microbes enter the stomach some may pass through before the acid kills them. They can breed further down the digestive system and cause disease.

Does the digestive system have any other way of getting rid of the harmful microbes?
Yes, it does. During the normal digestion of food a large amount of water from the digestive processes passes into the digestive system. In a healthy person, this water is absorbed by the wall of the large intestine and passed back into the blood. If the digestive system is infected with a harmful microbe the intestine does not take back the water and a person has diarrhoea. This watery substance helps to swill the harmful microbes out of the body.

Do any protozoans live in humans?
Yes, they do. There are some kinds of protozoans called amoeba which live in the mouth and do not cause harm. They move around in the slime on the teeth and gums as they feed. You may think of them as microscopic bags of jelly, which are always changing shape as they move. There is a kind of amoeba which can live in the intestine and cause harm. It produces the disease called dysentery. A feature of this disease is acute diarrhoea. This is the body's way of trying to rid itself of the microbe.

Do algae live on the body?
No, but they do live on the body of some animals. These animals are called sloths and they live in rainforests of South America. A sloth has fur made from long hair, which wraps around the body rather like a mat. There are grooves in the hair in which algae live. They collect the water from the fur when it rains on the animal and they receive the sunshine they need as the animal carries them about. In return, during the rainy season, the algae make the sloth's fur green. This helps to camouflage the sloth and protect it from predators.