tended 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 simulated adangerously hasty ascent to see what would happen。 what happened was that the dentalfillings in his teeth exploded。 鈥渁lmost every experiment；鈥潯orton writes； 鈥渆nded withsomeone having a seizure； bleeding； or vomiting。鈥潯he chamber was virtually soundproof； sothe only way for occupants to signal unhappiness or distress was to tap insistently on thechamber wall or to hold up notes to a small window。
on another occasion； while poisoning himself with elevated levels of oxygen； haldane hada fit so severe that he crushed several vertebrae。 collapsed lungs were a routine hazard。
perforated eardrums were quite mon； but； as haldane reassuringly noted in one of hisessays； 鈥渢he drum generally heals up； and if a hole remains in it； although one is somewhatdeaf； one can blow tobacco smoke out of the ear in question； which is a socialacplishment。鈥�
what was extraordinary about this was not that haldane was willing to subject himself tosuch risk and disfort in the pursuit of science； but that h