by Bill Mesler
Francesco Redi found van Helmont’s recipes about as credible as the stones brought by the Franciscans, as he did all such recipes based on spontaneous generation. He decided to put the theory to the test. He chose to focus on the fly. As anyone could plainly see, flies were not born in a conventional sense; they simply emerged from all manner of filth. People could say with absolute certainty that there was no such thing as a fly egg for the simple reason that nobody had ever seen one. But Redi had an epiphany when reading an account of spontaneous generation found in Homer’s Iliad. “What if it should turn out,” he later recounted, “that all the grubs that you find in flesh are derived of the seeds of flies and not through the rotting flesh itself?”
During July, the time of year when flies seemed to be at their most numerous, Redi placed a snake, a fish, some small eels, and a piece of raw veal into four different flasks, tightly enclosing each after they had been filled. He then did the same thing with four more flasks. These, though, he left open, exposed to the air and any insects that might happen by. Just as Redi expected might happen, maggots appeared on the rotting flesh in the open containers, but not in those he had shut off from the air.
The results supported Redi’s hypothesis, but he realized the experiment was not definitive. Anticipating his critics, he wondered whether the maggots failed to appear in the sealed jars because they needed air to survive. So he devised an even more ingenious experiment, using containers wrapped in gauze instead of sealed containers. Maggots did appear, but only on the outside of the gauze. For Redi, the only viable explanation was that flies had been drawn to the decaying meat, but, unable to penetrate the gauze, had laid their eggs on its surface.
School textbooks would one day remember it as the “Redi experiment.” What made it such a seminal event in the history of science was not so much what Redi had proved or disproved. It was, rather, how he had done it: by developing a hypothesis and creating two very different sets of experimental conditions to test his theory. It was one of the earliest and finest examples of a controlled scientific experiment. Provando e riprovando.
The life cycle of the fly, from Experiments on the Generation of Insects.
Soon, Redi was undertaking similar experiments with all kinds of insects. These formed the basis of his greatest work of science, Experiments on the Generation of Insects—for its time a masterpiece of careful observation and experiment. In it, Redi claimed to have disproved not only Aristotle’s theory of spontaneous generation, but the very belief that nature, free of the hand of God, could have given rise to life. An artful writer, Redi summarized poetically the beliefs held by the classical Greek philosophers who thought that nature alone had given birth to life:
Many have believed that this beautiful part of the universe which we commonly call the Earth, on leaving the hands of the Eternal, began to clothe itself in a kind of green down, which gradually increasing in perfection and vigor, by the light of the sun and nourishment of the soil, became plants and trees, which afforded food to the animals that the earth subsequently produced of all kinds, from the elephant to the most minute and invisible animalcule.
To Redi, such a vision was incompatible with nature’s laws. Echoing the words of the Dutch naturalist Jan Swammerdam, he wrote, “All life comes from an egg.”
REDI’S CAREER IN THE SCIENCES would prove to be relatively short-lived. In May of 1670, Grand Duke Ferdinando II fell ill. The official cause was “apoplexy,” a word then often used to describe what we would now call a stroke. Physicians attended him with the most sophisticated treatments they had at their disposal, applying hot irons to his forehead and smothering him with the flesh of dead pigeons. The treatments worked about as well as the stones said to ward against poison that the grand duke had once been given by the Franciscans. He died two days later.
The duke’s only son, Cosimo III, assumed the throne. His father had wanted to give Cosimo a modern scientific education, but the duchess Vittoria would have nothing of it. The new grand duke was his mother’s child in nearly every way. It was said that he never in his entire life smiled—a fact that his admirers took as a sign of his great religious devotion. His reign became remembered mostly for its oppressive laws against the city’s Jewish population, which had grown to Italy’s largest under his father’s benevolent rule. He was also obsessed with chastity, establishing laws against making love near windows or doors, and even against women admitting young men who were not relatives into their houses. Homosexuals were beheaded. A biographer would later describe Cosimo as “a devotee to the point of bigotry; intolerant of all free thought; hated by his wife; his existence a round of visits to churches and convents.”
Redi found his official position at court unchanged. He had long played the role of intermediary between Cosimo III and his father during their disputes, which were constant, and the new grand duke held Redi in some esteem. But Redi’s career of scientific inquiry was no longer a viable option, and the younger Cosimo shuttered the Accademia del Cimento.
Redi instead threw himself into a new academy devoted to Tuscan literature, the Accademia della Crusca. He helped write the first Tuscan dictionary and authored several epic poems. He became far more famous, in his time, for his poetry than his science. His greatest work, Bacco in Toscana, is still considered a masterpiece of Italian literature. It revolved around a man’s struggle to supplant the Roman god of wine. “So daring has that bold blasphemer grown, he now pretends to usurp my throne,” laments the vengeful god Bacchus in Redi’s epic poem.
Toward the end of his life, Redi’s health began to fail from epilepsy. According to some accounts, he embraced Catholic mysticism, spending his days bathing in holy oil and spent a fortune on ribbons rubbed on the bones of Saint Ranieri, said to have miraculous healing powers. His own descriptions of his conditions seemed to imply that they were the result of nervous hypochondria.
Though Redi’s great scientific work, Experiments on the Generation of Insects, was widely read, its true significance would have been lost to most people of the era. Redi had employed the tool of experimentation to ask whether life could truly come from nonlife. To him, it could not. And he was confident that he had proved the “fact” with an incontrovertible experiment. Yet few accepted that he had settled the question of spontaneous generation, because nobody could say definitively that they had seen a fly’s egg. Doubt often wants to grow at the foundation of truth.
But meanwhile, far to the north, in Holland, an obscure Dutch haberdasher had acquired a copy of Experiments on the Generation of Insects. He was quite sure that what Redi was saying was correct, and not just because he believed in the infallibility of Redi’s experimental methodology. He was quite sure because he had actually seen the egg.
THE EYE OF A GNAT
Suns are extinguished or become corrupted, planets perish and scatter across the wastes of the sky; other suns are kindled, new planets formed to make their revolutions or describe new orbits, and man, an infinitely minute part of a globe which itself is only an imperceptible point in the immense whole, believes that the universe is made for himself.
—PAUL-HENRI THIRY, Baron d’Holbach, Le système de la nature, 1770
IT IS 1664. Late in the summer. A boat is being steered through a lake just outside the Dutch town of Delft. It is being guided by a man in his early forties, with a small hint of a mustache, about 2 inches long, that looks like it was drawn by pencil. He wears a light-brown wig that settles on his shoulders, typical of the Dutch middle class to which he belongs.
The lake is called Berkelse Mere. It is tiny, barely a lake, and marshy. In places, it descends into bog. Its depths are uneven and tricky to maneuver. The fishermen are used to it, for the fish are abundant in Berkelse Mere, and said to be uncommonly delicious. But this man is a stranger to the waters. He is a townsman from Delft, a merchant who deals in cloth. His name is Antonie van Leeuwenhoek, and he is looking for something in the lake.
There is another thing that Berkelse Mere is known f
or, although some think it may be related to the wealth of fish. In the winter, its water appears quite normal. It is exceptionally clear, in fact. But by early summer, the water in Berkelse Mere begins to take on a milky-white hue. Eventually, it fills with puffy green masses that float like clouds beneath its surface. The locals say the masses spring from the heavy dew that forms at this time of year, which they call honeydew. Van Leeuwenhoek isn’t so sure. And he thinks he may know how to solve the mystery once and for all.
He steers the boat over to one of the floating green clumps, where he produces a glass vial. He scoops up some of the greenish water, taking it with him on the two-hour carriage ride back to his row house in town, where he lives with his wife and stepdaughter. He isn’t sure what he’ll find in the water. He has no inkling that the only world humankind has ever known is about to get infinitely bigger and that everything people think about the nature of life is about to be turned on its head.
He puts the specimen aside. For the rest of the day, he resumes his life as a modest draper who lives in a modest house in a modest town in Holland. Perhaps he attends to his business. Perhaps he spends time with his daughter, Maria, whom he cherishes, all his other children having died in infancy.
The next day, he returns his attention to the lake-water sample. With tweezers, he extracts a long, greenish strand, about the size of a human hair, from a droplet, ever so carefully. His mother was from an old family of brewers, and the strand reminds him of a copper worm, the coil used to cool beer and ale during the brewing process. He sets it within a strange contraption that he, himself, built. It is a metal plate, about 10 inches long, attached to a metal clamp that looks like something a carpenter would use to mount a device on a workbench. He uses this clamp as a pedestal for drawing things up to the center of his metal plate, where he has drilled a hole to hold a tiny piece of glass that he has ground into a lens. The device is called a microscope, and the haberdasher from Delft has constructed one that enables him to see things smaller than anyone else on Earth can see, or has ever seen.
Van Leeuwenhoek places a drop of water onto his device and carefully looks into the lens. He sees something. It appears to be a tiny white oval. What’s more, it has what look like legs near what he imagines to be a head. And on the opposite side of the oval are things that look like fins. It is, he thinks to himself, a thousand times smaller than the smallest insect he has ever seen. When he sees it suddenly move, very quickly, darting like an eel through water, he is quite certain that it is alive.
FOR EVERY SINGLE human being on Earth, there are a billion trillion microbes. They thrive nearly everywhere—buried in rock 2,000 feet belowground, at three times that depth beneath the sea, and even within our bodies. A human being plays host to ten times as many microbial cells as human cells. Yet throughout most of history, humans were unaware of these ubiquitous life-forms with which we share the Earth. We wandered about, blind to the teeming jungle of tiny life-forms that we always mistook for a barren desert. The microscopic creatures that van Leeuwenhoek observed in his drop of water from Berkelse Mere were the first glimmers indicating that the world was much more densely populated by life than human beings had ever imagined.
It was fitting that the world of bacteria, protozoa, and countless other microbes was discovered during the seventeenth century. That century saw the world and human beings’ understanding of it begin to expand in unprecedented ways, and the year of van Leeuwenhoek’s birth, 1632, was important for a couple of very contradictory reasons.
On the one hand, 1632 marked the halfway point of the deadliest war Europe had ever known, or ever would know until the twentieth century. It was the war between Catholics and Protestants known, at the time, simply as the Great War. Historians would later give it the name by which it is usually remembered, the Thirty Years’ War. The countryside of much of central Europe had been transformed into a vast battlefield reminiscent of the macabre paintings of van Leeuwenhoek’s fellow Dutchman, Hieronymus Bosch. Whole towns and cities were wiped off the map. Even deadlier than the armies were the multitudes of diseases that followed in their wake. The population was beset by “head disease” and “Hungarian disease.” Typhus, bubonic plague, dysentery, and scurvy all took their toll. Amid the chaos, fanatics engaged in mass slaughter and religious pogroms. Some fifty thousand women and men were accused of witchcraft and hanged, drowned, burned alive, or impaled on stakes.
But the year 1632 was also a year that foretold hope in Europe, the dawn of a new age of science and reason that would come to be known as the Enlightenment. If science had begun to trickle back into the intellectual landscape of Europe during the Renaissance, during the Enlightenment it would gush like a deluge. And an astounding number of the most important figures of the Enlightenment were born in 1632. One was the Englishman John Locke, whose concept of the natural rights of all people, as opposed to the absolute power of the monarch, would inspire Enlightenment thinkers such as Voltaire and Jean-Jacques Rousseau, and underpin democratic revolutions in the Americas and France. Another was the Dutch Jewish philosopher Baruch Spinoza, who turned to rationality to explore spirituality, viewing God not as the creator of nature, but as nature itself. He would leave such a mark on the world of philosophy that the German philosopher Georg Wilhelm Friedrich Hegel would one day remark, “You are either a Spinozist or not a philosopher at all.”
Holland would become one of the centers of the Enlightenment. Delft, its capital at the time, would see two great figures born that year, van Leeuwenhoek and the painter Jan Vermeer, who would go on to create the masterpiece The Girl with the Pearl Earring. Vermeer’s revolutionary use of color and light would carve out a place for him among the most influential artists in history. The houses where he and van Leeuwenhoek were born were just a short walk from each other.
VAN LEEUWENHOEK’S FATHER, Philips, was a basket maker who had married into a family of brewers, which was a respectable trade in seventeenth-century Holland. Philips had married above his station, which wasn’t uncommon in the Netherlands. While the lives of most Europeans were mapped out by rigid lines of status and privilege, such distinctions were beginning to fall apart in Holland. The Enlightenment was opening the European world up to a much broader class of people. The Dutch began to believe that a man should be able to succeed because of his abilities, not the circumstances of his birth. Dutch women were also winning rights far beyond what women in most of Europe enjoyed or could even imagine. A gentlewoman could speak her mind freely and walk the streets unchaperoned without raising eyebrows. For the first time anywhere, wife beating became a crime.
Tiny Holland was rapidly becoming the center of European trade, with more ships than Spain, England, Portugal, France, and Austria combined. The Dutch had become the middlemen of Europe, moving goods between faraway colonies—those of their former enemies, as well as their own in places like the island of Java in modern-day Indonesia and New Amsterdam, situated on the island of Manhattan and destined to become the American city of New York. The Dutch began to talk of their Gouden Eeuw, their “Golden Age.”
Along with Holland’s newfound wealth came unprecedented freedoms, which helped make it a center of scientific progress in the Europe that emerged from the Thirty Years’ War. Those freedoms extended even to religion, where the Calvinist Dutch believed in the separation between church and state. Communities of Jews, Lutherans, and even their recent enemies, Catholics, commingled and flourished in seventeenth-century Holland. At a time when religious strife so dominated the rest of Europe, a Dutchman like the painter Jan Vermeer faced few obstacles converting to Catholicism, while elsewhere such a conversion might have forced him to flee his nation or, at the least, might have hindered his career. Spinoza’s writings, considered blasphemous at the time, earned the philosopher a writ of cherem—essentially an excommunication—from the Jewish temple to which he belonged, and he was reviled by the Calvinists. Yet his writing never landed him in prison, nor was he even in serious danger of prosecution. Near
ly two centuries later, in England, the atheist poet Percy Bysshe Shelley would be tried for posting a single blasphemous handbill while he was a college student, and his atheism would eventually lead the British state to take his children away.
Immigrants from nearly everywhere were drawn to Holland’s freedoms. Many, like Johannes van Helmont, were great scientific minds, and scientific theorizing flourished free of censorship from Rome. Dutch printing presses began to be filled with scientific treatises written in the Netherlands and abroad. Amsterdam became the first place where Galileo’s banned work on the heavens, Mechanics, could be published. For many years, it was the only place.
The concept of a professional scientist did not yet exist. The very word “science,” from the Latin word scientia (“knowledge”), was used sparsely, unlike the more common term “natural philosophy.” Yet there was a class of great thinkers who we, in retrospect, classify as scientists. Most, like the physician Francesco Redi, had a day job. Van Helmont was likewise a physician, though he was often referred to as a philosopher. They were, by and large, men of a certain level of social status who could afford to devote time and money to studies that others usually saw as something of a hobby.
There was one thing all these natural philosophers had in common: education. Their ranks were filled by some of the most learned men of their eras. This was something van Leeuwenhoek did not share with his contemporaries. His father died when he was five. His mother and new stepfather sent him away for some perfunctory primary schooling. Latin and Greek were virtually mandatory for any fairly well educated person at the time; thus the playwright Ben Jonson could make light of his contemporary, William Shakespeare, for having “small Latin and little Greek.” Van Leeuwenhoek had neither. He would go on to win credit for some of the most important scientific advances of the age, and to rub shoulders with the leaders of the world’s most powerful countries. Yet he always seemed slightly out of place, insecure, and thin-skinned.