Bill Bryson - A short history of nearly everything

Other organisms do of course manage to deal with the pressures at depth, though quite how some of them do so is a mystery. The deepest point in the ocean is the Mariana Trench in the Pacific. There, some seven miles down, the pressures rise to over sixteen thousand pounds per square inch. We have managed once, briefly, to send humans to that depth in a sturdy diving vessel, yet it is home to colonies of amphipods, a type of crustacean similar to shrimp but transparent, which survive without any protection at all. Most oceans are of course much shallower, but even at the average ocean depth of two and a half miles the pressure is equivalent to being squashed beneath a stack of fourteen loaded cement trucks.

Nearly everyone, including the authors of some popular books on oceanography, assumes that the human body would crumple under the immense pressures of the deep ocean. In fact, this appears not to be the case. Because we are made largely of water ourselves, and water is “virtually incompressible,” in the words of Frances Ashcroft of Oxford University, “the body remains at the same pressure as the surrounding water, and is not crushed at depth.” It is the gases inside your body, particularly in the lungs, that cause the trouble. These do compress, though at what point the compression becomes fatal is not known. Until quite recently it was thought that anyone diving to one hundred meters or so would die painfully as his or her lungs imploded or chest wall collapsed, but the free divers have repeatedly proved otherwise. It appears, according to Ashcroft, that “humans may be more like whales and dolphins than had been expected.”

Plenty else can go wrong, however. In the days of diving suits-the sort that were connected to the surface by long hoses-divers sometimes experienced a dreaded phenomenon known as “the squeeze.” This occurred when the surface pumps failed, leading to a catastrophic loss of pressure in the suit. The air would leave the suit with such violence that the hapless diver would be, all too literally, sucked up into the helmet and hosepipe. When hauled to the surface, “all that is left in the suit are his bones and some rags of flesh,” the biologist J. B. S. Haldane wrote in 1947, adding for the benefit of doubters, “This has happened.”

(Incidentally, the original diving helmet, designed in 1823 by an Englishman named Charles Deane, was intended not for diving but for fire-fighting. It was called a “smoke helmet,” but being made of metal it was hot and cumbersome and, as Deane soon discovered, firefighters had no particular eagerness to enter burning structures in any form of attire, but most especially not in something that heated up like a kettle and made them clumsy into the bargain. In an attempt to save his investment, Deane tried it underwater and found it was ideal for salvage work.)

The real terror of the deep, however, is the bends-not so much because they are unpleasant, though of course they are, as because they are so much more likely. The air we breathe is 80 percent nitrogen. Put the human body under pressure, and that nitrogen is transformed into tiny bubbles that migrate into the blood and tissues. If the pressure is changed too rapidly-as with a too-quick ascent by a diver-the bubbles trapped within the body will begin to fizz in exactly the manner of a freshly opened bottle of champagne, clogging tiny blood vessels, depriving cells of oxygen, and causing pain so excruciating that sufferers are prone to bend double in agony-hence “the bends.”

The bends have been an occupational hazard for sponge and pearl divers since time immemorial but didn’t attract much attention in the Western world until the nineteenth century, and then it was among people who didn’t get wet at all (or at least not very wet and not generally much above the ankles). They were caisson workers. Caissons were enclosed dry chambers built on riverbeds to facilitate the construction of bridge piers. They were filled with compressed air, and often when the workers emerged after an extended period of working under this artificial pressure they experienced mild symptoms like tingling or itchy skin. But an unpredictable few felt more insistent pain in the joints and occasionally collapsed in agony, sometimes never to get up again.

It was all most puzzling. Sometimes workers would go to bed feeling fine, but wake up paralyzed. Sometimes they wouldn’t wake up at all. Ashcroft relates a story concerning the directors of a new tunnel under the Thames who held a celebratory banquet as the tunnel neared completion. To their consternation their champagne failed to fizz when uncorked in the compressed air of the tunnel. However, when at length they emerged into the fresh air of a London evening, the bubbles sprang instantly to fizziness, memorably enlivening the digestive process.

Apart from avoiding high-pressure environments altogether, only two strategies are reliably successful against the bends. The first is to suffer only a very short exposure to the changes in pressure. That is why the free divers I mentioned earlier can descend to depths of five hundred feet without ill effect. They don’t stay under long enough for the nitrogen in their system to dissolve into their tissues. The other solution is to ascend by careful stages. This allows the little bubbles of nitrogen to dissipate harmlessly.

A great deal of what we know about surviving at extremes is owed to the extraordinary father-and-son team of John Scott and J. B. S. Haldane. Even by the demanding standards of British intellectuals, the Haldanes were outstandingly eccentric. The senior Haldane was born in 1860 to an aristocratic Scottish family (his brother was Viscount Haldane) but spent most of his career in comparative modesty as a professor of physiology at Oxford. He was famously absent-minded. Once after his wife had sent him upstairs to change for a dinner party he failed to return and was discovered asleep in bed in his pajamas. When roused, Haldane explained that he had found himself disrobing and assumed it was bedtime. His idea of a vacation was to travel to Cornwall to study hookworm in miners. Aldous Huxley, the novelist grandson of T. H. Huxley, who lived with the Haldanes for a time, parodied him, a touch mercilessly, as the scientist Edward Tantamount in the novel Point Counter Point .

Haldane’s gift to diving was to work out the rest intervals necessary to manage an ascent from the depths without getting the bends, but his interests ranged across the whole of physiology, from studying altitude sickness in climbers to the problems of heatstroke in desert regions. He had a particular interest in the effects of toxic gases on the human body. To understand more exactly how carbon monoxide leaks killed miners, he methodically poisoned himself, carefully taking and measuring his own blood samples the while. He quit only when he was on the verge of losing all muscle control and his blood saturation level had reached 56 percent-a level, as Trevor Norton notes in his entertaining history of diving, Stars Beneath the Sea , only fractionally removed from nearly certain lethality.

Haldane’s son Jack, known to posterity as J.B.S., was a remarkable prodigy who took an interest in his father’s work almost from infancy. At the age of three he was overheard demanding peevishly of his father, “But is it oxyhaemoglobin or carboxyhaemoglobin?” Throughout his youth, the young Haldane helped his father with experiments. By the time he was a teenager, the two often tested gases and gas masks together, taking turns to see how long it took them to pass out.

Though J. B. S. Haldane never took a degree in science (he studied classics at Oxford), he became a brilliant scientist in his own right, mostly in Cambridge. The biologist Peter Medawar, who spent his life around mental Olympians, called him “the cleverest man I ever knew.” Huxley likewise parodied the younger Haldane in his novel Antic Hay , but also used his ideas on genetic manipulation of humans as the basis for the plot of Brave New World . Among many other achievements, Haldane played a central role in marrying Darwinian principles of evolution to the genetic work of Gregor Mendel to produce what is known to geneticists as the Modern Synthesis.