万物简史英文版_比尔·布莱森-第45章
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on 400 million years ago to crawl out of the seas andbee land based and oxygen breathing。 in consequence； no less than 99。5 percent of theworld鈥檚 habitable space by volume； according to one estimate； is fundamentally鈥攊n practicalterms pletely鈥攐ff…limits to us。
it isn鈥檛 simply that we can鈥檛 breathe in water； but that we couldn鈥檛 bear the pressures。
because water is about 1；300 times heavier than air； pressures rise swiftly as you descend鈥攂y the equivalent of one atmosphere for every ten meters （thirty…three feet） of depth。 on land；if you rose to the top of a five…hundred…foot eminence鈥攃ologne cathedral or the washingtonmonument； say鈥攖he change in pressure would be so slight as to be indiscernible。 at the samedepth underwater； however； your veins would collapse and your lungs would press to theapproximate dimensions of a coke can。 amazingly； people do voluntarily dive to such depths；without breathing apparatus； for the fun of it in a sport known as free diving。 apparently theexperience of having your internal organs rudely deformed is thought exhilarating （though notpresumably as exhilarating as having them return to their former dimensions uponresurfacing）。 to reach such depths； however； divers must be dragged down； and quite briskly；by weights。 without assistance； the deepest anyone has gone and lived to talk about itafterward was an italian named umberto pelizzari； who in 1992 dove to a depth of 236 feet；lingered for a nanosecond； and then shot back to the surface。 in terrestrial terms； 236 feet isjust slightly over the length of one new york city block。 so even in our most exuberantstunts we can hardly claim to be masters of the abyss。
other organisms do of course manage to deal with the pressures at depth； though quite howsome of them do so is a mystery。 the deepest point in the ocean is the mariana trench in thepacific。 there； some seven miles down； the pressures rise to over sixteen thousand pounds persquare inch。 we have managed once； briefly； to send humans to that depth in a sturdy divingvessel； yet it is home to colonies of amphipods； a type of crustacean similar to shrimp buttransparent； 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 isequivalent to being squashed beneath a stack of fourteen loaded cement trucks。
nearly everyone； including the authors of some popular books on oceanography； assumesthat 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鈥渧irtually inpressible；鈥潯n the words of frances ashcroft of oxford university； 鈥渢he bodyremains at the same pressure as the surrounding water； and is not crushed at depth。鈥潯t is thegases inside your body； particularly in the lungs； that cause the trouble。 these do press；though at what point the pression bees fatal is not known。 until quite recently it wasthought that anyone diving to one hundred meters or so would die painfully as his or her lungsimploded or chest wall collapsed； but the free divers have repeatedly proved otherwise。 itappears； according to ashcroft； that 鈥渉umans may be more like whales and dolphins than hadbeen expected。鈥�
plenty else can go wrong； however。 in the days of diving suits鈥攖he sort that wereconnected to the surface by long hoses鈥攄ivers sometimes experienced a dreadedphenomenon known as 鈥渢he squeeze。鈥潯his occurred when the surface pumps failed； leadingto a catastrophic loss of pressure in the suit。 the air would leave the suit with such violencethat the hapless diver would be； all too literally； sucked up into the helmet and hosepipe。
when hauled to the surface； 鈥渁ll that is left in the suit are his bones and some rags of flesh；鈥�
the biologist j。 b。 s。 haldane wrote in 1947； adding for the benefit of doubters； 鈥渢his hashappened。鈥�
（incidentally； the original diving helmet； designed in 1823 by an englishman namedcharles deane； was intended not for diving but for fire…fighting。 it was called a 鈥渟mokehelmet；鈥潯ut 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； butmost especially not in something that heated up like a kettle and made them clumsy into thebargain。 in an attempt to save his investment； deane tried it underwater and found it was idealfor salvage work。）the real terror of the deep； however； is the bends鈥攏ot so much because they areunpleasant； though of course they are； as because they are so much more likely。 the air webreathe is 80 percent nitrogen。 put the human body under pressure； and that nitrogen istransformed into tiny bubbles that migrate into the blood and tissues。 if the pressure ischanged too rapidly鈥攁s with a too…quick ascent by a diver鈥攖he bubbles trapped within thebody 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 thatsufferers are prone to bend double in agony鈥攈ence 鈥渢he bends。鈥�
the bends have been an occupational hazard for sponge and pearl divers since timeimmemorial but didn鈥檛 attract much attention in the western world until the nineteenthcentury； and then it was among people who didn鈥檛 get wet at all （or at least not very wet andnot generally much above the ankles）。 they were caisson workers。 caissons were encloseddry chambers built on riverbeds to facilitate the construction of bridge piers。 they were filledwith pressed air； and often when the workers emerged after an extended period ofworking under this artificial pressure they experienced mild symptoms like tingling or itchyskin。 but an unpredictable few felt more insistent pain in the joints and occasionally collapsedin agony； sometimes never to get up again。
it was all most puzzling。 sometimes workers would go to bed feeling fine； but wake upparalyzed。 sometimes they wouldn鈥檛 wake up at all。 ashcroft relates a story concerning thedirectors of a new tunnel under the thames who held a celebratory banquet as the tunnelneared pletion。 to their consternation their champagne failed to fizz when uncorked inthe pressed air of the tunnel。 however； when at length they emerged into the fresh air of alondon evening； the bubbles sprang instantly to fizziness； memorably enlivening thedigestive process。
apart from avoiding high…pressure environments altogether； only two strategies are reliablysuccessful against the bends。 the first is to suffer only a very short exposure to the changes inpressure。 that is why the free divers i mentioned earlier can descend to depths of five hundredfeet without ill effect。 they don鈥檛 stay under long enough for the nitrogen in their system todissolve into their tissues。 the other solution is to ascend by careful stages。 this allows thelittle bubbles of nitrogen to dissipate harmlessly。
a great deal of what we know about surviving at extremes is owed to the extraordinaryfather…and…son team of john scott and j。 b。 s。 haldane。 even by the demanding standards ofbritish intellectuals； the haldanes were outstandingly eccentric。 the senior haldane was bornin 1860 to an aristocratic scottish family （his brother was viscount haldane） but spent mostof his career in parative modesty as a professor of physiology at oxford。 he wasfamously absent…minded。 once after his wife had sent him upstairs to change for a dinnerparty 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 ideaof a vacation was to travel to cornwall to study hookworm in miners。 aldous huxley； thenovelist grandson of t。 h。 huxley； who lived with the haldanes for a time； parodied him； atouch mercilessly； as the scientist edward tantamount in the novel point counter point 。
haldane鈥檚 gift to diving was to work out the rest intervals necessary to manage an ascentfrom the depths without getting the bends； but his interests ranged across the whole ofphysiology； from studying altitude sickness in climbers to the problems of heatstroke in desertregions。 he had a particular interest in the effects of toxic gases on the human body。 tounderstand more exactly how carbon monoxide leaks killed miners； he methodically poisonedhimself； carefully taking and measuring his own blood samples the while。 he quit only whenhe was on the verge of losing all muscle control and his blood saturation level had reached 56percent鈥攁 level； as trevor norton notes in his entertaining history of diving； stars beneaththe sea； only fractionally removed from nearly certain lethality。
haldane鈥檚 son jack； known to posterity as j。b。s。； was a remarkable prodigy who took aninterest in his father鈥檚 work almost from infancy。 at the age of three he was overhearddemanding peevishly of his father； 鈥渂ut is it oxyhaemoglobin or carboxyhaemoglobin？鈥�
throughout his youth； the young haldane helped his father with experiments。 by the time hewas a teenager； the two often tested gases and gas masks together； taking turns to see howlong it took them to pass out。
though j。 b。 s。 haldane never took a degree in science （he studied classics at oxford）； hebecame a brilliant scientist in his own right； mostly in cambridge。 the biologist petermedawar； who spent his life around mental olympians； called him 鈥渢he cleverest man i everknew。鈥潯uxley likewise parodied the younger haldane in his novel antic hay； but also usedhis 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 togeneticists as the modern synthesis。
perhaps uniquely among human beings； the younger haldane found world war i 鈥渁 veryenjoyable experience鈥潯nd freely admitted that he 鈥渆njoyed the opportunity of killing people。鈥�
he was himself wounded twice。 after the war he became a successful popularizer of scienceand wrote twenty…three books （as well as over four hundred scientific papers）。 his books arestill thoroughly readable and instructive； though not always easy to find。 he also became anenthusiastic marxist。 it has been suggested； not altogether cynically； that this was out of apurely contrarian instinct； and that if he had been born in the soviet union he would havebeen a passionate monarchist。 at all events； most of his articles first appeared in themunist daily worker。
whereas his father鈥檚 principal interests concerned miners and poisoning； the youngerhaldane became obsessed with saving submariners and divers from the unpleasantconsequences of their work。 with admiralty funding he acquired a depression chamberthat he called the 鈥減ressure pot。鈥潯his was a metal cylinder into which three people at a timecould be sealed and subjected to tests of various types； all painful and nearly all dangerous。
volunteers might be required to sit in ice water while breathing 鈥渁berrant atmosphere鈥潯rsubjected to rapid changes of pressurization。 in one experiment； haldane s
