Susan Wedlich wants us to care deeply about slime, and she musters all the rhetorical tricks at her disposal to achieve her goal. “Does even the word ‘slime’ have to elicit gagging histrionics?” she exclaims, berating us for our phobia. “If we neither recognise nor truly know slime, how are we supposed to appreciate it or use it for our own ends?”
Slippery, ubiquitous, oozing slime is the stuff of life. “Most organisms use slime for a number of functions, be it as a structural material, as jellyfish do; for propagation, as plants do; to catch prey, as frogs do; for defence, like the hagfish; or for movement, like snails,” Wedlich, a German science journalist, points out.
Slime certainly spooks our imagination. Think of the slimy jaws of the creature in Alien, or the creeping terrors of HP Lovecraft’s stories. For more than 2,000 years, since Greek and Roman antiquity, sailors have been haunted by the notion of a “motionless sea”; ships, it is said, have been caught fast and even foundered in waters turned to slime. Slime stalks the febrile dreams of landlubbers too: Jean-Paul Sartre raved for several pages of his 1943 essay Being and Nothingness about “le visqueux”. Its “soft, yielding action, a moist and feminine sucking”, lovingly quoted here, had this reader instinctively scrabbling for the detergent. We’ve learnt to fear slime in a way that would have seemed quite alien to the farmers of ancient Egypt, who supposed slime and mud were the base materials of life itself.
Despite it being everywhere, we do not necessarily know enough about slime. To take one example, using slime to read our ecological future turns out to be a vexed business. There’s a scum of nutrients held together by slime floating on top of the oceans; a fraction of a millimetre thick, it’s called the “sea-surface microlayer”. Global warming might be thinning it, or thickening it, and either might be accelerating, or retarding, climate change. So there: yet another thing to worry about.
For sure, slime holds the world together. Or rather slimes: there are any number of ways to solidify water so that it acts as a lubricant, a glue or a barrier. Whatever its origins, it is most conspicuous when it disappears, such as when the gluey glycan coating of one’s blood vessels starts to mysteriously shear away during surgery, or when overtilling of America’s Great Plains destroyed the slime-strengthened soil crust and caused the Dust Bowl in 1933.
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Slime is the unlovely poster child of environmental degradation, and Wedlich argues that if we don’t do something sharpish to change our ecological ways “we risk a new ‘slime surge’ if our soon-to-be-empty oceans are home only to jellyfish, algae and microbial mats”.
Hand in hand with such millennial anxieties, of course, come the usual power fantasies: that we might harness all this unlovely slime — nothing more than water held in a cage of a few long-chain polymers — to transform our world, providing the base for new materials and soft robots, “transparent, stretchable, locomotive, biocompatible, remote-controlled, weavable, wearable, self-healing and shape-morphing, 3D-printed or improved by different ingredients”.
Wedlich’s enthusiasm is by no means misplaced. Slime is not just a largely untapped wonder material. It is also — really, truly — the source of life, and a key enabler of complex forms. We used to think the machinery of the first cells must have risen in clay hydrogels — a rather complicated and unlikely genesis — but it turns out that nucleic acids such as DNA and RNA can sometimes form slimes on their own. Life, it turns out, does not need a substrate on which to arise. It is its own sticky home.
The role of slime in the human body is evident enough, from lubricant tears to the mucosal plug that waxes and wanes at the mouth of the cervix.
In our bodies, four hydrogel (slime) systems form a tightly interwoven barrier which transports respiratory gases and nutrients even as it wards off intruders. (More than 1000 million microbes can find their way into the body every day simply in the meals we eat.) These layers are populated by trillions of useful microbes including bacteria, fungi and archaea, which are a kind of single-celled living fossil predating multi-cellular life.
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Wedlich’s tour of the human gut, and its multiple slime layers — some lubricant, some gluey, and many armed with extraordinary electrostatic and molecular traps for one pathogen or another — is a tour de force of clear and gripping explanation.
Slime being, in essence, nothing more than stiffened water, there are more ways to make it than the poor reader could bear to hear about. So Wedlich very sensibly approaches her subject from the other direction, introducing slimes through their uses. Snails combine gluey and lubricating slimes to travel over dry ground one moment and cling to the underside of a leaf the next. Hagfish deter predators by jellifying the waters around them, shooting polymers from their skin like so many thousands of microscopic harpoons. Some squid, when threatened, add slime to their ink to create pseudomorphs — fake squidoids that hold together just long enough to distract a predator. Some squid pump out whole legions of such doppelgangers.
Wedlich’s own strategy, in writing Slime, is not dissimilar. She’s deliberately elusive. The reader never really feels as though they have got hold of the matter of her book; rather, they are being provoked into punching through layer after dizzying layer, through theories about the spontaneous generation of life, through the life cycles of carnivorous plants and into the tactics of Japanese balloon-bomb designers in the Second World War, until, dizzy and gasping, they reach the end of Wedlich’s extraordinary mystery tour, not with a handle on slime exactly, but with an elemental new vision of what life may be: that which arises when the boundaries of earth, air and water are stirred in sunlight’s fire.
Slime: A Natural History by Susan Wedlich, trans. Ayça Türkoglu, Granta, 336pp; £20
