Never Home Alone

1

WONDER

THERE IS NO singular origin story of the study of the wilderness of life in homes, but a day in Delft in 1676 comes close. Antony van Leeuwenhoek had walked the block and a half from his house to the market to buy black pepper. He strolled past the fish market, the butcher, and the town hall. He paid for the pepper, thanked the vendor, and then returned home. Once home, Leeuwenhoek did not sprinkle the pepper in his food. Instead, he carefully added a third of an ounce of the black stuff to a teacup filled with water. He then let the water and pepper steep. He was trying to soften the peppercorns so he could break them open and, in doing so, discover what it was inside them that led them to be spicy. Over the coming weeks, he checked on the peppercorns again and again. Then, after about three weeks, he made what was to prove a pivotal decision. He decided to draw a sample of the pepper water itself up into a thin tube of glass he had blown. The water seemed surprisingly cloudy. He examined it through a kind of microscope, a single lens affixed to a metal frame. This setup worked well for translucent things, such as pepper water, or for the thin sections of solid materials he would later teach himself to make.¹

When Leeuwenhoek looked through his lens at the pepper water, he saw something unusual. Figuring out just what it was took some fidgeting and finessing. He either moved his candle this way and that, if working at night, or maybe he moved himself this way and that, if he was working using light from his window. He tried multiple samples. Then, on April 24, 1676, he finally had a clear view. What he saw was truly special: “an incredible number of very little animals of diverse kinds,” as he put it. He had seen microscopic life before, but never anything quite so small. He would repeat this procedure in various permutations a week later, then again, then again with ground pepper, then with pepper in rainwater, then with other spices, each substance infused in his teacup. Each time he did this, he saw ever more life. These were the first sightings of bacteria by a human. And they were sightings being made in a home while studying materials that can be found in any kitchen, black pepper and water. Leeuwenhoek was at the edge of the wilderness, the miniature wilderness of his own home. He had seen a dimension of this living world that had never been seen before. The question remained whether anyone would believe what he had seen.

Leeuwenhoek probably started using microscopes to study the life around him, in his home and beyond, a decade prior in 1667. The moment when Leeuwenhoek saw bacteria in pepper water came only after hundreds, maybe thousands, of hours spent searching his home and daily life more generally. Chance does, indeed, favor the prepared mind, but it favors the obsessed mind even more. Obsession comes to scientists naturally enough. It emerges when one mixes focus and relentless curiosity. It can strike anyone.

Leeuwenhoek was not a scientist in the traditional sense. By trade, he worked with fabrics and sold cloth, buttons, and other related bits and pieces out of a shop in his home in Delft.² Leeuwenhoek likely began to use lenses of some kind to inspect the fine threads of particular fabrics.³ But something then motivated him to explore other things in his home. It may have been a book published by Robert Hooke, Micrographia.⁴ Leeuwenhoek spoke only Dutch, so he would have been unable to read Hooke’s text, but the pictures of what Hooke had seen through his own microscope could have been inspiration enough.⁵ From what we know of Leeuwenhoek’s personality, it is easy to imagine him, after having seen the pictures, using the first Dutch-English dictionary (published in 1648) to puzzle through paragraph after paragraph of Hooke’s words.

By the time Leeuwenhoek started to look through his microscope, other scientists had already used microscopes to see new details of home-dwelling creatures. Those scientists, including Hooke, found previously unsuspected patterns in life’s interstices, patterns that suggested a world beyond that which was known. A flea’s leg, a fly’s eye, and the long-stalked spore cases (sporangia) of the fungus Mucor growing on a book cover in Hooke’s home, all revealed minutiae not previously seen, or even imagined. We can examine the same species today, using the same magnification, but when we do our experience is very different from what it would have been in the 1600s. We already know that microscopic details exist even if we are surprised when we encounter them firsthand. For the scientists working in the early days of microscopy, the experience was more surprising, akin to discovering secret messages scrawled across each surface of the living world, messages no one else had ever seen.

As Leeuwenhoek peered through microscopes at the life in and around his home, he, too, saw new details. He saw the flea, for example, and drew many of the details that Hooke had drawn, but he also saw things Hooke had missed. He saw the flea’s seminal vesicles, each no larger than a sand grain. He even saw the flea’s sperm inside those vesicles, which he then compared to his own sperm.⁶ As he continued to search, he began to notice entire life-forms that had never before been seen, life-forms entirely invisible without a microscope. These weren’t overlooked details; Leeuwenhoek had found something more significant: he had discovered what we now call protists, a grab bag of single-celled life-forms united only by their size. They divided. They moved. And there were many kinds, some larger, some smaller, some hairy, some smooth, some with tails, some without, some attached to surfaces, and others unmoored.

Leeuwenhoek told people he knew in Delft about his discoveries. He had many friends, be they fishmongers, surgeons, anatomists, or nobles. One of those friends was Regnier de Graaf, who lived not far from Leeuwenhoek. De Graaf was a young man and yet already very accomplished. By the time he was thirty-two, he had discovered, for example, the function of the fallopian tubes. Leeuwenhoek’s discoveries made such an impression on de Graaf that on April 28, 1673, he sent a letter to Henry Oldenburg, the secretary of the Royal Society in London, on Leeuwenhoek’s behalf, despite the fact that he was mourning the death of a newborn child. In the letter, de Graaf noted that Leeuwenhoek had amazing microscopes and urged Oldenburg and the Royal Society to give Leeuwenhoek some specific assignments to pursue, subjects on which to focus with his microscope and skill. De Graaf also enclosed some of Leeuwenhoek’s notes about his discoveries.

Upon receiving the letter, Oldenburg wrote back directly to Leeuwenhoek and asked him for figures to accompany his descriptions.⁷ In August, Leeuwenhoek responded (by which time de Graaf had tragically died), adding more details about the things he had seen but that others (including Hooke) had missed: the physical appearance of mold, the stinger of a bee, the head of the bee, the eye of the bee, the body of a louse. Meanwhile, Leeuwenhoek’s first letter, the letter that de Graaf had shared on his behalf, was published on May 19 in the Philosophical Transactions of the Royal Society, the second oldest scientific journal in the world, at that time still in just its eighth year. This was to be the first of many letters, letters akin to what one might now find in a blog post. The letters were not heavily edited; nor were they always structured. They were often digressive and repetitive. But these daily observations of the small things in his house and town were novel; they were observations of scenes no one had ever seen before. It was in one of these letters, sent on October 9, 1676, letter eighteen, that Leeuwenhoek recorded his observations about the pepper water.⁸

LEEUWENHOEK SAW PROTISTS in the pepper water. Protists include many kinds of single-celled organisms, each more closely related to animals, plants, or fungi than to bacteria. Leeuwenhoek described what appear to have been protist species of the bacteria-feeding genera Bodo, Cyclidium, and Vorticella. Bodo has a long whip-like tail (flagellum), Cyclidium is covered with wiggling hairs (cilia), and Vorticella attaches itself to surfaces by a stalk (and filters water for food). But then he also spotted something else. The smallest of the organisms in the pepper water were, he calculated, one one-hundredth the width of a grain of sand and one-millionth the volume. In retrospect, we know something so small could only be a bacterium. But in 1676, bacteria had never been seen by humans before; this was their grand reveal. Leeuwenhoek was thrilled, as he was quick to note to the Royal Society,

The Royal Society had been pleased with Leeuwenhoek’s first seventeen letters. However, with the letter on pepper water, he had finally gone too far, strayed from the path of truth toward that of pure imagination. Robert Hooke in particular balked. Hooke, thanks to the success of Micrographia, was the acknowledged king of the microscopic and had never seen anything so small alive. Hooke and another well-established member of the Royal Society, Nehemiah Grew, proceeded to try to repeat Leeuwenhoek’s observations with an eye toward proving them false. It was part of what the society did, stage and repeat experiments. Usually they were done as simple demonstrations. In this case, however, the experiment was undertaken both as a demonstration and to determine whether or not the results Leeuwenhoek reported were true.

NEHEMIAH GREW WAS the first to try to repeat Leeuwenhoek’s observations. He failed. Hooke took it upon himself to try. Hooke repeated each of the steps Leeuwenhoek took with the pepper, water, and microscope and he saw nothing. He grumbled. He scoffed. But he also tried again. He tried harder. He made better microscopes. On his third attempt, he and ultimately the other members of the Royal Society began, finally, to see some of what Leeuwenhoek had seen. In the meantime, Leeuwenhoek’s pepper water letter, which had been translated into English by Oldenburg, was published by the Royal Society. With the publication of this letter, and the confirmation of Leeuwenhoek’s observations by the Royal Society, the scientific study of bacteria—bacteriology—began. Notably, it began with the study of a bacterium found in a mix of ordinary kitchen pepper and water, a bacterium found indoors.

Three years later, Leeuwenhoek repeated the pepper experiment, but this time he kept the pepper water in a sealed tube. In the tube, the bacteria used up the oxygen that was present and yet something continued to grow, and bubble. Leeuwenhoek had once again discovered something new with the pepper water, this time the existence of anaerobic bacteria, bacteria able to grow and divide without oxygen. He once again made this new discovery while studying the life in his own home. The study of bacteria in general and the study of anaerobic bacteria in particular both began with the study of the life in a house.

We now know that bacteria are everywhere—in places with and without oxygen, in hot places and cold places, in every place—a layer, sometimes thin and sometimes thick, of life on each and every surface, inside each and every body, in the air, in the clouds, and at the bottom of the sea. Tens of thousands of bacterial species have been identified and millions (perhaps trillions) of other species are thought to exist. But in 1677, the bacteria Leeuwenhoek and a few members of the Royal Society had discovered were the only bacteria known in the world.

LEEUWENHOEK’S WORK IS sometimes discussed, both historically and today, as though the man simply used a new tool to study the world around him and, in doing so, revealed new worlds. In this telling, the story is all about the microscope and its lens. The reality is more complex. Today, you can fasten a microscope of the same magnification as Leeuwenhoek used to your camera. (And you should.) If you do, you can use it to search around your house, but you will not see the world the way Leeuwenhoek did. Leeuwenhoek’s discoveries did not result simply because he possessed a diversity of very good microscopes with well-made lenses. The discoveries depended on his patience, persistence, and technical abilities. It wasn’t the microscopes that were magical but rather the combination of the microscopes and his careful hands and wonder-filled mind.

Leeuwenhoek was better at seeing this world, in all its grandeur, than anyone else. But doing so took work that others considered to be impossibly hard. So the members of the Royal Society, despite having seen the world Leeuwenhoek discovered, failed to continue to study it in any real earnestness. After verifying Leeuwenhoek’s observations of microbes, Hooke continued to look at microscopic life through his own microscopes for about six months. But then he was done. Hooke and other scientists left the new world to Leeuwenhoek. Leeuwenhoek was to become an astronaut of the miniature, all alone exploring a realm that was more diverse and elaborate than anyone but him seemed to understand.

For the next five decades of his life, Leeuwenhoek systematically documented each and every thing around him; he documented all of Delft and beyond (often through samples brought to him by friends), but especially the living contents of his house. Anything he stumbled across was fair game. He studied the water in gutters, the water in rain, the water in snow. He detected microbes in his own mouth, and then in his neighbor’s mouth. He observed living sperm (again and again) and showed how it varied among species. He showed that maggots arose from the eggs of flies rather than spontaneously from filth. He documented, for the first time, a kind of wasp that lays its eggs inside the bodies of aphids. He noticed, for the first time, that adult wasps survive the winter by slowing down and going quiescent. Over his years of dedicated study, he saw many kinds of protists for the first time, the first storage vacuoles,¹⁰ the banded patterns in muscles. He discovered organisms living in the rind of cheese, in wheat flour, everywhere. He searched, he saw, he wondered, he discovered, again and again and again throughout the fifty years of his ninety-year life. He was like Galileo, dumbfounded and inspired. But whereas Galileo had to satisfy himself with looking out at the universe and the movements of stars and planets as tests of his predictions, Leeuwenhoek could touch the world he had found. He could discover the life in water and then drink the water, the life in vinegar and then use the vinegar, the species on his own body and then go about his life.

Because it is hard to match Leeuwenhoek’s descriptions of the life around him to the modern names of species, we can’t tally just how many life-forms he might have seen, but it was certainly in the thousands. It is tempting to draw a straight line from Leeuwenhoek to the modern study of the life in homes, but this would be wrong. Upon Leeuwenhoek’s death, the study of the life in homes for its own sake was largely abandoned. Though Leeuwenhoek inspired the masses, he had no true colleagues in Delft after the death of de Graaf.¹¹ His daughter may have worked with him during his later years, but she did not follow up on his observations after he died. While she was alive she kept his specimens and microscopes, but they went unused. After she died, as Leeuwenhoek himself had specified in his will, they were auctioned off. Most of his microscopes disappeared. The gardens where he made observations were subsumed by the growing edges of Delft. His childhood home, where his inspiration must have first flourished, fell into disrepair and was torn down in the nineteenth century; in its place now stands a playground for a school. The house in which he made so many discoveries was torn down too.¹² A plaque was mounted to note the place where his house stood, but it was set in the wrong place. Another plaque was placed to remedy the error of the first; it, too, is not quite in the right location (one or two houses off depending on how one counts).

Eventually, other scientists would begin to study the life on human bodies and in homes anew. But by the time this happened, more than a hundred years had passed and it had been discovered that some microbial species could cause disease. These species were called pathogens. The idea that pathogens cause disease is the germ theory, credited to Louis Pasteur (though by the time Pasteur demonstrated that microscopic species could cause human disease it was already established that microscopic species could cause diseases in crop plants). With the advent of germ theory, pathogens became the focus of studies of microbial life indoors. Leeuwenhoek seems to have had an inkling that microscopic species could cause problems (he’d shown that some microbes could turn good wine into bad vinegar). He just imagined that most of the life he was seeing was harmless. In this, Leeuwenhoek was right. Of all the bacterial species in the world, for instance, fewer than fifty regularly cause disease. Just fifty. All the rest of the species are either benign or beneficial to humans, as are nearly all protists and even viruses (viruses wouldn’t be discovered until 1898, though they too were discovered in Delft). Once pathogens were known to be part of the invisible world, war was declared upon all invisible life indoors. The closer that life was to us, the more exhaustive the war. The study of peppercorns, gutter water, and the whimsical, whirling creatures found everywhere in the average home was abandoned. Time would make this abandonment ever more complete.

By 1970, nearly the only studies being done in homes focused on pathogens and pests and how to control them. The microbiologists who studied homes studied how to kill pathogens. Nor was it just the microbiologists. The entomologists who studied homes studied how to kill insects. The plant biologists who studied homes studied how to get rid of pollen. The food scientists who studied pepper considered whether it might be a source of food-borne illness. We forgot about the potential of the life around us to inspire wonder and left no room for the realization that the species around us might not only plague us but also help us. We became focused on only part of the story. This was a big mistake, one we have only very recently begun to remedy. The first big steps back toward a more holistic view of the life around us were taken at hot springs—in Yellowstone National Park and in Iceland—places that seem to have nothing to do with homes at all.