ASHES to ashes. Dust to dust. Death comes to everyone, and decay follows soon after. At least, it usually does. But now and then, something-either chance or design-holds putrefaction at bay, and a body becomes a mummy. We're so fascinated by the "living dead" that you'd think we would have worked out exactly how these bodies are preserved. Of course we understand the broad outline-freezing, drying and certain chemicals prevent bacteria and human enzymes from breaking down tissues-but the finer details are only now beginning to emerge, thanks to a few intrepid researchers who've decided to make mummies of their own.
Take Egyptian mummies. We know that dehydration was the key here, depriving bacteria of the water they need to go about their business. But the Egyptian embalmers kept their exact methods a trade secret, and archaeologists never knew whether the few descriptions written by outsiders held the complete recipe followed by mummy makers. "It was quite a secretive profession, and you would question whether the embalmers would have given away their secrets to a foreign visitor," says Richard Evershed from the University of Bristol.
So Bob Brier, an Egyptologist at Long Island University, decided the only way to find out if ancient historians had left out important details was to make his own mummy, following their instructions. In 1994, he and his colleague Ronn Wade from the University of Maryland got their hands on the fresh corpse of an elderly Baltimore man who had donated his body to science, and set to work.
Following descriptions recorded by the Greek historian Herodotus and others, they extracted his brain and abdominal organs and then packed the body cavity with linen bags of natron, a mix of salt with sodium carbonate and bicarbonate that Brier had dug from dry salt lakes in Egypt for historical accuracy. They then covered the corpse in a 264-kilogram heap of the stuff and put it in a hot, dry room. There they left it for 35 days, half expecting to find a putrid lump of flesh when they returned.
When they finally opened the room, their noses heralded better news. "It had a fishy, peppery odour," recalls Wade. "I wouldn't say it was pleasant, but it wasn't obnoxious." Sure enough, when they cleared away the natron, the body had dried. "In a sense, we were looking at an Egyptian mummy for the first time," says Brier. "And what was shocking was that it looked just like a mummy-that leathery brown-and to a great extent felt like a mummy." In other words, 3000 years of storage has little effect on many real mummies.
The natron had drawn out more than half the body's weight in water, with only the buttocks and a few parts of the back retaining enough water and oils to be pliable. After examining the body closely, the two researchers oiled it and packed the cavity with spices and wood shavings. Then they wrapped it in linen-in ancient Egypt this would have protected the body from nibbling insects, as well as giving it a more lifelike plumpness-and stored it away. Their mummy is now seven years old, and shows no signs of deterioration-which suggests, says Brier, that simple dehydration is the key to mummification.
Or is it? "I think there's a bit more to it than that," says Evershed, who believes that the application of oils, waxes and resins to the body surface after drying plays a crucial role, not the mere ceremonial purpose that Brier ascribes to it. "The tombs are rather damp places. Maybe they found that things would rehydrate if you didn't then take further steps to waterproof them and add some antibacterials." When Evershed and his colleague Stephen Buckley looked at the chemical composition of coatings used on 13 Egyptian mummies they found that all but one-the least well preserved-included plant resins or beeswax, which are known to inhibit bacterial growth (Nature, vol 413, p 837). Most also contained vegetable oils, which spontaneously polymerise to a lacquer-like protective coating. "It's why you add linseed oil to your cricket bat or an oil painting," says Evershed. Together, these coatings help prevent a mummy gradually deteriorating over centuries, he thinks.
The Egyptians undoubtedly had mummification down to a fine art, but mummies can form without any human intervention. Now and then, a body freezes quickly after death and stays frozen-deep in a glacier, say, or in a grave dug into Arctic permafrost. If protected from drying winds, such bodies can remain almost perfectly preserved for centuries. More often, however, exposure causes them to lose water through sublimation, a form of natural freeze-drying that can remove nearly three-quarters of the body's original weight. Any thawing and refreezing before drying is complete wreaks havoc with the structure of cells, which explains why the tissues of most high-Arctic mummies are nearly unrecognisable under the microscope.
Then there are the bog bodies. How human remains are preserved in bogs is something of a mystery. The answer can't be simple, because the bodies vary widely in condition. "We don't really know why some bog bodies are so well preserved and others not," says Don Brothwell from York University. There's no doubt, though, that in a watery grave, cold and lack of oxygen can be enough to slow decay to a crawl. "A body in that environment will not decompose at the same rate as if I'd buried it in the back garden," says Rob Janaway from Bradford University. He should know, because he and his colleague Andrew Wilson have buried pigs in waterlogged soils on the Yorkshire moors. After six months, says Wilson, "you can see pretty much a whole pink pig with skin, muscle tissue and internal organs well preserved." A year on, the body still looks much more intact than one buried in drier, more aerated soil. And some tissues are likely to last much longer still-even in normal graves, hair and fingernails can survive for hundreds of years.
Submersion clearly plays a vital part in the creation of bog bodies. In another porcine experiment, Brothwell's student, Heather Gill-Robinson, buried six young piglets within a single square metre of peat bog in northern England. Two and a half years later, two had rotted to skeletons, two had some soft tissue preserved, and two were nearly intact. "The only difference was that the two that were best preserved were in the wettest part of that square," says Gill-Robinson, now at the University of Manitoba in Winnipeg.
Few bacteria or other decomposers can survive in cold, oxygen-poor waters, but some bogs also contain a more exotic preservative. Sphagnan is an unusual, complex sugar molecule found in the leaves of sphagnum moss, the main plant growing in peat bogs. The sphagnan molecule contains many carbonyl groups, which react with amine groups on proteins. One effect of this is to inactivate enzymes, says biochemist Terence Painter. "We have here quite a marvellous preservative," he says. "The bacteria must have a very frustrating time. They are presented with a beautiful body, but as soon as they start secreting the enzymes to break it down, the enzymes become bound and inactivated on the leaves of the sphagnum."
Painter also credits sphagnan with a role in creating the classic bog body look. "The skin changes texture from a light, thin skin to a tougher, more tanned one," says Gill-Robinson. Commercial leather tanners attain this effect with formaldehyde, which creates chemical cross-linking in proteins, and sphagnan seems to do exactly the same thing. "The simplest way of understanding why a body gets preserved in peat is to imagine you had submerged it in a solution of formaldehyde," says Painter. His conclusion seems plausible, but the jury is still out. Evershed used sophisticated trace-analytical techniques to search for organic tanning agents in skin taken from bog bodies, but drew a blank.
Clearly the living dead are not yet prepared to reveal all their secrets. But with plans afoot for more pig burials and research to see what's going on at the molecular level, it seems likely we'll work it out in the end. It may be some time, however, before we can unwrap the mystery of the mummies.
New Scientist issue: 8th December 2001
PLEASE MENTION NEW SCIENTIST AS THE SOURCE OF THIS STORY AND, IF PUBLISHING ONLINE, PLEASE CARRY A HYPERLINK TO: http://www.newscientist.com