SIR RANULPH FIENNES and Dr Michael Stroud, survivors of a world record first unsupported crossing of the Antarctic, will now complete medical research into the effects of extreme conditions on the human body.

The emphasis is on extreme. The explorers' journey of 1,350 miles was over a continent that is one-tenth of the earth's land surface, yet more than 98 per cent covered with ice. Antarctica contains 90 per cent of the world's ice and is the remotest, highest, coldest and driest continent. The closest large city is 1,000 miles away and the lowest temperature ever recorded on earth was found there: minus 89C (minus 128F).

Blizzards of 200mph sweep over a monotonous sheet of white ice, making this the most inhospitable medical laboratory in the world. Yet research into human responses under these conditions has many uses.

As early as 1968, before anyone had set foot on the moon, Nasa was interested in these results for space missions of long duration. In 1978 Nasa sponsored the first conference on 'The human experience in Antarctica: applications to life in space', and valuable lessons learnt by polar explorers are being used to prepare people for venturing into other remote places - for instance, a trip to Mars.

When the US explorer Admiral Richard Byrd went to Antarctica in the Twenties, he took with him a dozen straitjackets and two coffins. Although many of the reasons for fits of insanity among early explorers, such as vitamin deficiencies, are now routinely corrected, the isolation imposed by these conditions is still unique. Not only is travel to and from the Antarctic impossible during winter, which lasts up to nine months in some parts of the continent, but even radio communications may be interrupted by atmospheric conditions.

The three most potent sources of stress are isolation, monotony and the absence of hobbies or interests. Under these strains severe psychological problems are a constant risk; in the Fifties one expedition leader reported on a man in a depressed state: '. . . he threatened to shoot himself, but was successfully dealt with by a companion in very down- to-earth fashion. 'Look, mate,' he said, 'I have put a .45 revolver over on that oil drum, loaded. You go over and shoot yourself. But just in case you think of shooting someone else instead, or if you should miss with your first shot, remember I have a loaded .303 right here.' '

In an environment in which people cannot be replaced once winter has begun, appropriate personnel selection becomes a matter of life and death. On one American Antarctic base just after the Second World War, a man became severely psychotic and had to be watched constantly for months until winter lifted. Since then a priority has been placed on the screening of polar staff.

One of the first to be confronted with selection problems was Sir Ernest Shackleton, whose 1913 solution was a typically robust newspaper ad: '. . . men wanted for hazardous journey . . . small wage, bitter cold, long months of complete darkness . . . safe return doubtful . . .'

He received 5,000 applications for 28 positions. A comment on British pluck, or the state of the job market?

Research suggests that the successful personality for surviving Arctic conditions differs in many respects from that most likely to flourish in conventional society. For example, sophisticated social graces cease to have significance. The continent becomes a haven for the technically competent who are deficient in social skills; it seems to suit the introverted and reserved. This ties in with the finding that the withdrawn and shy adapted better to the highly abnormal conditions of Nazi concentration camps than did more sociable prisoners.

Thanks to modern psychological selection techniques, polar camps have not suffered repetitions of the unfortunate experiences of the Fifties. However, insomnia is still a big problem, associated with feelings of depression during the winter that are spontaneously resolved in summer. As the Antarctic winter is characterised by perpetual night for months on end, these abnormal day lengths are thought to throw internal biological clocks out of sync.

Winter depression in polar regions has been cured by simple exposure to two hours' artificial high-intensity light every day. This treatment is used successfully for those suffering from the very similar Seasonal Affective Disorder (SAD) in Britain. SAD may be the modern counterpart of 'cabin fever', which afflicted remote communities during winter and was blamed for their homicidal and suicidal reputations.

Compared with these psychiatric problems, physical disorders are relatively rare in Antarctica; bacteria cannot exist in the extreme cold, but there is a tendency for tooth enamel to crack in low temperatures, which means that a dentist is often more useful than a doctor. The ice is more than two miles thick in some areas, which makes Antarctica one of the highest regions above sea level in the world. The available oxygen at the South Pole is equivalent to that at 10,200ft on a mountain range, making altitude sickness common. Symptoms include headaches, light-headedness, vomiting, fatigue, rapid breathing and dehydration.

Yet with all these problems, many people reapply for duty in Antarctica. It seems that the isolation and difficulties lead to strong, intimate relationships between colleagues, bonds of mutual concern and obligation that Antarctic travellers find missing in urban society.

Despite its physical remoteness, Antarctica holds many lessons. Above the continent we rely on the strength of its ozone layer, while on its surface it continues to teach us, better than any psychiatrist, the true quality of the human spirit.

(Photograph omitted)