On a clear spring day, I make my way to the Hunterian Museum in Glasgow. It’s located in a part of the university campus which has a whiff of Hogwarts about it, with a maze of courtyards, the entrance hiding somewhere within. The Hunterian is the oldest public museum in Scotland, more cabinet of curiosities than modern scientific institution. Roman artefacts, feathered Maori cloaks and fossils sit side by side in this museum, which reminds me of a church with its pointy gable and simple rosette glass window, the high ceiling worked in the same dark wood as the carved balustrades. But it’s neither the neo-Gothic charm nor the wonderful collections that brought me to the Hunterian. I am here to see a glass bottle, about as big as a hand, fitted with a fat stopper and two gilded labels, handwritten. I’m here to see an old phial filled with slime.
Some forms of matter seem to unite the properties of solids and liquids. For example, cats: which category do they fall into? The answer should be an easy one, physically speaking: solids retain their shape, while liquids fill their container. Cats seem unequivocally to be solids, until they demonstrate their aptitude for easily slipping into the smallest of gaps, almost flowing into them. The French physicist Marc-Antoine Fardin researched, tongue-in-cheek, the physical classification of cats between solid and liquid, touching on his specialist area of rheology, the study of the flow of matter. In 2017 he was awarded the Ig Nobel Prize, a not altogether serious award for suitably original research.
Matter which exists somewhere between solid and liquid is not restricted to cats, though, and slime is its most important embodiment in nature. It is protean in its behaviour; it is the material of interfaces and has a unique place in our imaginations. We are all creatures of slime, but some of us are more creative than others: there is a menagerie of oozing organisms to be found in all the world’s habitats, frequently changing these environments to suit their needs – by leaving their glistening marks. It may also be a surprise to discover that microbes were not only the dominant, but also the only form of life on Earth for billions of years, with slime, as the éminence gluante, propping up their power and setting in motion processes across the globe which still shape it today.
The long reign of slime concerns the supposedly boring stages of evolution which preceded the emergence of the first animals. Popular portrayals often neglect this seemingly endless span of time, but slime was paving the way for life on Earth then, particularly for higher organisms like us. It may even have facilitated our very existence. It is a legacy we humans prefer to ignore. Here, we benefit from slime’s hidden nature, with its visible manifestations banished inside our bodies. Better not to think about slime, which seems to carry the scent of our baser instincts, of sex and weakness, of sickness and death. We regard it as an object of universal disgust, only admitting it – at least in industrialized societies – into our hyper-hygienic worlds in controlled doses, as an entertaining expression of the depths of the human psyche.
Modern monsters can rarely do without slime and slobber, be it on screen in movies like Alien or in stories like the ones H.P. Lovecraft wrote. In a sense, slime makes humans biological creatures, yet becomes the line of demarcation between us and the Other. Is this because slime as a phenomenon is slippery to grasp but nonetheless elicits strong emotions? Physically speaking, it can be defined and therefore contained. Slime is an extremely aqueous and viscously fluid hydrogel, which also bears the properties of a solid under certain conditions. Biological slimes are so flexible that they can easily adapt as required. Scientists are trying to copy or emulate these sophisticated structures for applications like soft robots, smart wound dressings or tailor-made glues, but often come unstuck when attempting to unravel their biological complexity.
Yet the first steps have been taken and, in the future, it may be possible to imitate even more specialized slimes, which serve as the adhesives, lubricants and selective barriers vital to microbes, animals and plants. There is probably no single living creature that does not depend on slime in some way. 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. The ubiquity of slime is little recognized, because many biological hydrogels hide behind pseudonyms like ‘mucilage’, ‘mesoglea’, ‘marine snow’ and, of course, ‘mucus’, which barely give an inkling of their true and common nature.
Since many of these biological hydrogels are secreted outwards, they work beyond the single organism. Even in the natural environment they are invisible cement, holding different ecosystems together, from desert to coastline to marine habitats, primarily at the interfaces where water, land and air meet. Slime is a central cog in the world we live in and even slight changes could have global effects. The looming reality of climate change and other environmental crises like the loss of ecosystems and biodiversity threatens hydrogel-based relationships and processes. However, a new equilibrium in a warmer world might also favour slime in some habitats, allowing it to return to dominance. It would be a step back into an early era of evolution, a new era of slime.
The importance of slime is similarly far-reaching inside the human organism, equipped as it is with four different gel-like systems to fortify it with living walls, gates, armour and moats. Most pathogens founder at these defences, while welcome microbes find refuge as tenants and mercenaries. Like materials science and climate research, biomedicine has been waking up to its own ‘slime blindness’; defective hydrogel barriers have an important part to play in infections, chronic intestinal inflammations, cystic fibrosis, cancer, heart attacks and a series of other ailments.
Without slime we would be overrun by pathogens: hydrogels are sticky traps for microbial invaders which actually produce slime as well. Keeping our distance from unknown hydrogels is expedient and our aversion to all things slimy well-founded, as the science of disgust shows. But does even the word ‘slime’ have to elicit gagging histrionics? Our all-too-often highly emotional response to viscous materials can lead to ignorance as we forget that slime is the very foundation of our biology, an essential for our health and our environment. And that kind of ignorance is a very modern idea.
In Ancient Egypt, mud and slime were thought of as a source of life. Aristotle’s works on the theory of spontaneous generation of insects and other lowly animals was then supported for many centuries. It received an unexpected boost when Charles Darwin’s theory of evolution overthrew biblical ideas on the origins of nature. Could primordial slime on the ocean floor be the source of life? This claim was made by the prominent Darwinist Ernst Haeckel (1834–1919) and it electrified early evolutionary biology for a brief period in the second half of the nineteenth century.
Haeckel was fortunate to live in an age when the technological revolution opened access to the deep sea for the first time. Samples from the floor of the Atlantic Ocean seemed to confirm his theory. They contained a gelatinous mass which he quickly declared to be primordial slime; it even seemed to move – especially when observed on board a ship on the high seas. It was Haeckel’s misfortune to live during the dawn of the discipline of oceanography and its rigorous analytical technology. His theory was tested when HMS Challenger embarked upon an expedition lasting many years and spanning the globe. Instead of charting the habitat of primordial slimes, it ultimately exposed Haeckel’s hypothesis as a boozy mistake.
In Glasgow around 145 years later, it is this specimen that I’m hoping to trace: the find which disproved the theory of primordial slime as giver of life. On 4 March 1876, the crew of HMS Challenger brought up some matter from the ocean floor of the South Atlantic.To their surprise, the specimen did not contain any pulsating primordial slime; it was just seawater. Only once the sample had been properly preserved in plenty of alcohol did a gelatinous mass appear inside the glass vessel. But it was merely a mineral precipitate, resulting from a reaction between seawater and alcohol. And so the brief era of primordial slime was over. The only things left are an amusing anecdote and the specimen from the Challenger expedition, which I struggle at first to find at the Hunterian, though I comb through every cabinet in every hall and in the gallery.
The primordial slime phantasm wasn’t Haeckel’s sole contribution to early evolutionary biology – nor the most controversial, either. He was one of the most prominent advocates of an ‘evolutionary racism’ that accorded human lives unequal value. Nowadays he is best known as a natural scientist and gifted artist who made gelatinous sea creatures so popular in science and among the public that art nouveau took inspiration from his drawings of their graceful silhouettes. Haeckel based his system of nature on primitive organisms, little more than the smallest units of slimy protoplasm. This was the name given to the gelatinous, pulsing substance inside cells, which according to a popular theory was the most basic expression of life.
As such, protoplasm was even believed to be capable of receiving invisible signals from the outside world. Towards the end of the nineteenth century, a new and exciting age dawned; people began to think of themselves as surrounded and permeated by vibrations and oscillations coming from the ether, an invisible and possibly gelatinous medium thought to span the entirety of space. If the transmission of sound, light and energy could be traced back to oscillations, would similar vibrations influence the protoplasm, the substance of life itself? According to some theories, their traces – a bit like grooves on a vinyl record – created individual patterns of experience, to be stored and bequeathed to the next generation. When it came to unseen impulses from the ether, artists were considered to be extremely sensitive and even capable of perceiving the world as a whole. Luminaries like the painter Edvard Munch tried to find a new science-based language for the arts to convey that experience to their audiences. Psychic mediums were another conduit for the ethereal realm, all the more believable when a kind of protoplasm flowed plentifully from their bodies. Or so it seemed. The First World War brought a boom in contacting the other side, while protoplasmic collaborations between empirical sciences and the arts came to an end. The world of trenches and death marches through muddy ‘slimescapes’ was one of men hard in body and spirit, without a place for seemingly feminine softness and yielding. Twenty years ago, an article on snails in the New Scientist prompted me to think about slime not as some unknowable phenomenon but as a material with specific chemical compounds, physical properties and biological functions. I thought about writing a book then, but envisioned some sort of glorified leaflet or small booklet at most. What was there to know about slime, anyway? But then ever more aspects of this fascinating material revealed themselves to me, often as chance discoveries; one detail would lead me to a new anecdote, which was connected to a little-known publication that opened yet more doors.
Slime and evolution: spanning billions of years. Slime and the planet: glueing global cycles and processes together. Slime and life: a foundation to us and all organisms. Slime in the lab: technology going soft. Slime on paper: linking nature and art. Slime and monstrosity: a trigger of disgust. Little by little, enough pieces of the puzzle came together: slime is neither an accident nor an exceptional presence in the world. It is an omnipresent rule. That makes a definitive book on slime an improbable feat. The material is too varied, its evolution too long and our love-hate relationship with it too volatile.
This book is an attempt to span more than one great arc with chapters that can be read in sequence or independently. Not every reader will be interested in every single facet of slime and might skip some parts. This is why I repeat fundamental terms and processes as required. But reader, be warned: this is a sprawling story, bursting at the seams and hard to contain at times. When it comes to slime, there are no hard borders or distinct divisions, or a chronology to connect the dots. Please indulge yourself with the dripping and oozing glory of slime. You won’t get lost if you follow the signs.
The Phenomenon section explores slime as an often emotionally charged concept and monstrous prop. Physics examines the material and its unique properties, while Organism looks at the significance of gels for the body. Before disgust came high regard, as the origins and the very essence of Life were traced back to primordial forms of slime, in science and modern art. Slime is indeed a companion of all life, a pioneer of Evolution, whose secrets we have only begun to unlock. So, has Nature spawned a single slime-free creature? It’s hard to imagine, because gels have many uses, depending on habitat and organism. They also shape the outward appearance of our Environment. Climate change and other catastrophes threaten this balance, but could also work in slime’s favour, ushering in a new era of gooey dominance.
Primordial slime? Never heard of it, replies a staff member at the Hunterian when I enlist her help. But she begins to search, even recruiting two colleagues, themselves equally in the dark when it comes to the slime’s location. We fan out and search for a long time before they finally bring me the good news that there are several bottles of historical goo. Could my slime be among them? And they’re right: I find the phial from the Challenger expedition in a glass cabinet in the main hall. It’s so high up and out of the way that I had missed it altogether. It is surrounded by other historical treasures from marine research trips: dried mud from the ocean floor and a pickled lungfish, dolefully observing the goings-on below. One of the staff gets me a ladder, bringing me eye to eye with the slime. In storage for so long, the gelatinous mass has disintegrated, and the bottle looks to be filled with clear water. Only at the bottom is a delicate, shimmering layer of white, barely perceptible to the eye. It seems fitting that this historical goo no longer exists, since primordial slime never really did either. It’s also fitting for many of the other slimes in this book, which, at least when I embarked upon my research, I could sense more than see. Slime rarely has its place in the spotlight, though it holds us and our worlds together. It’s high time we run towards the blob and take a closer look.