A few weeks ago a mother gave her dying son a piece of her liver. He had acute liver failure, and would have died within 48 hours if he hadn't received it. Wonderfully, the operation worked. She is fit and well, her liver back to normal size and full working order, and he will grow up into a normal adult.

It is a fantastic story, and one that does great credit to the scientists who developed the transplant systems and to the surgeons who perfected the operation. For the liver is an extremely complex organ, with many jobs to do. It's not like fitting up the plumbing, as in a heart or kidney transplant.

The liver sits in the upper abdomen, just behind the lower right ribs. You can't feel it in a healthy person, as its lower edge lies just behind the lower rib margin. But if it is swollen or enlarged, then it can be felt as a firm mass as far down as the navel. That's why doctors take so much care over feeling gently, with the flat of their fingers, all over the stomach wall when they suspect possible liver trouble.

The liver is our great chemical factory. It takes the digested remnants of our food direct from the gut, and turns it into the substances we need to keep us alive. It provides us with the glucose we need for our immediate energy needs, with fats for energy storage, and for important organ structures.

For example, our fattiest organ is the brain - nerve cells are full of complicated fats, and the liver provides them all. And it manufactures all the proteins we need for body structure - bones, muscles, sinews, tubing, the lot. It provides, and secretes into the circulation, the building blocks for all the chemicals made by other organs. Without the liver, we would have no hormones or blood cells, no functioning brain, no senses, no organisation, no consciousness, no life.

It is our biggest rubbish disposal system. Just the normal actions of everyday life produces a host of waste products, from broken-down muscle, blood and other specialised cells to used-up residues of hormones and a myriad of other chemicals. It "de-toxifies" poisons, adding subtle chemicals to them to make them harmless. And for poisons read alcohol, drugs such as paracetamol, and the tars inhaled by smokers.

It gets rid of these waste substances in two ways - it passes some on to the bloodstream, so that the kidneys deal with them, and it passes the rest into the bile, which passes via a tube into the gut. Bile itself is an amazing concoction of substances that digests fats and helps the body to take up various vitamins and minerals from food.

So a healthy liver is essential in so many ways - we abuse it at our peril. Of course everyone knows that too much alcohol over a long period is a liver killer. Which is why the experts advise restricting it to a dose that the liver can cope with - no more than three average drinks a day, and preferably with two to three days a week without it, to give the organ a break.

Fewer people realise that drugs can kill livers, too. Even a relatively small overdose of paracetamol can poison the liver permanently, so that the only treatment for some people is a transplant. Women are particularly unlucky in this respect, because the liver systems that deal with poisons also deal with the residues of female sex hormones. Sometimes their livers can't cope with both, so that they are much more at risk than men taking a similar overdose of drug.

The most certain way to wreck your liver, though, is to start misusing so-called "recreational" drugs. Everyone by now has heard that they can catch HIV from needle and syringe sharing - but what about hepatitis viruses? They are around a hundred times more infective than HIV, and over the years many of the infections they cause are just as deadly.

We know now of at least four hepatitis viruses, and there are certainly more. Injecting infected material into your bloodstream is the most efficient way to kill off your liver known to man - and if you share injecting materials there is no way they can be clean or guaranteed free of infection.

I'm staggered by the immense risks people are prepared to take, just for a fix. I just wish I knew how to get the message of healthy living through to them.

Converted for the new archive on 30 June 2000. Some images and formatting may have been lost in the conversion.