FORTY THREE years ago today, at 11.30 am on May 29th, 1953, Edmund Hillary and Sherpa Tensing stood together on Mount Everest, the first people to have scaled the highest mountain in the world. "I have no feeling of extreme pleasure or excitement Hillary recalled, "but more a sense of quiet satisfaction and even of surprise." The pair spent IS minutes on the summit taking photographs, and having left behind the flags of their respective nations together with some sweets and biscuits the latter a Buddhist offering from Tensing they began the long descent.
Mountain tops, even on a much smaller scale that Everest, are inhospitable to human beings, and were for centuries associated with a mysterious malady known as "mountain sickness". When it was discovered that atmospheric pressure decreases with altitude, it was assumed that this phenomenon was in some way culpable, but not until the 1880s did one Paul Bert show conclusively that the ill effects were due, not to the mechanical consequences of diminishing pressure, but to lack of oxygen.
Atmospheric pressure at 29,000 ft, the height of Everest, is a mere 300 hectopascals compared with 1,000 down at sea level. Since the relative proportions of the different gases in the atmosphere remain constant with increasing height, the rarefied air at this altitude contains only one third of the amount of oxygen to which humans are accustomed. The symptoms of hypoxia, or lack of oxygen, are quite alarming.
At first the body fries to compensate by hyperventilation by increasing both the depth and frequency of breathing. Heart and pulse accelerate, headache, nausea, and dizziness set in, and judgment is impaired as if by alcohol. The ultimate effects were described as early as AD 403 by the Chinese writer Huio Jiao, who plied the silk route over the Himalayas and recorded the illness of his fellow travellers. "The wind was chilling to the bones on the shady north side of the Lesser Snowy Mountains. Jui Jing was in a serious condition, frothing at the mouth, losing his strength rapidly, and fainting now and then. Finally he dropped dead on the snowy ground."
The obvious way to avoid the worst affects of mountain sickness is to bring along your own supply of oxygen, as Hillary and Tensing did. Given time, however, the body can acclimatise itself to rarer air, provided the transition is allowed to take place very slowly. Thus it was that 25 years after the events described above, a physiological feat of equal importance was achieved on May 8th, 1978, Reinhold Messner and Peter Habeler reached the top of Everest without the aid of artificial oxygen.