The Seeds of Life Page 11

  One week later, on November 7, Hooke tried again. He had found a way to make even narrower tubes, and he had changed the design of the microscope so that it admitted more light. And he had made an extra-strong concoction of pepper-water, by leaving the pepper grains soaking for a full three days. “Notwithstanding the microscope was much better than that shown at the last meeting,” the Royal Society’s records declared, “yet nothing of Mr. Leeuwenhoek’s animals could be seen.” Perhaps the excitable Dutchman had somehow gone wrong?

  By his third try, on November 15, Hooke had finally triumphed. He had tinkered and fussed throughout the week, and he had let the pepper steep for ten days. In the days leading up to the meeting, he had repeatedly seen the animalcules, and now he showed everyone. There they were! “There could be no fallacy,” the Royal Society agreed. “They were near an hundred thousand times less than a mite,” and they made “all manner of motions to and fro in the water, and by all who saw them, they were verily believed to be animals.”

  The records of the Royal Society carefully noted the names of the eyewitnesses who saw this marvelous sight. Christopher Wren, who had designed St. Paul’s Cathedral and done pathbreaking work in astronomy as well, headed the list. In modern terms, it would be as if the National Science Foundation had reported finding dinosaurs living on a remote island in the Pacific and had recruited Stephen Hawking and other luminaries to vouch for the discovery.

  THE ROYAL SOCIETY NOW BELIEVED LEEUWENHOEK, BUT NO one, not even Hooke, could match his wizardry with a microscope. Leeuwenhoek raced ahead of the pack, with no one else truly even in second place. In long, chatty reports that careened from topic to topic, Leeuwenhoek detailed his journeys through the microcosmos. To a hasty reader, his letters might have looked like the obsessive screeds that turn up on every editor’s desk, but it took only a few minutes to see that these notes were thick with revelations.

  Leeuwenhoek wrote in Dutch, the only language he knew. This counted as a strike against him, as if a correspondent today sent learned journals handwritten articles rather than electronic documents. (For seventeenth-century readers, Leeuwenhoek’s letters had a distinctly down-market tone. “Testicles,” for instance, were zaad-ballen, “seed-balls.”) All proper scholars wrote in Latin. Unable to read their work, Leeuwenhoek found himself confined inside a Dutch-speaking bubble.

  The independence may have suited him. Eager for praise but wary of collaborators, he went his own way.* In mingled fascination and frustration, the Royal Society followed his higgledy-piggledy progress. Everything intrigued Leeuwenhoek. He told the Royal Society about a spider with hairs that “stood as thick upon his Carcass as the Bristles on a Hog’s back.” He nearly blinded himself trying to see what happens when gunpowder explodes. He cajoled whalers newly returned to port into providing him blubber samples. (The flesh “did not smell at all good, because it was rather tainted,” but Leeuwenhoek was not a squeamish man.)

  He watched attentively as “an hungry Lowse” perched on his hand “to observe her drawing blood.” Family and servants pitched in. Perhaps they had little choice. When Leeuwenhoek grew curious about silkworm eggs and how they hatched, he recruited his wife, Cornelia, to help keep the eggs warm. For six weeks, she gamely traipsed about with a small box of silkworm eggs “carried in her Bosom night and day.” For another investigation, mother and daughter stood with mouths open wide while Leeuwenhoek poked between their teeth with a toothpick, in search of samples.

  He had already found the inside of the mouth to be an especially rich hunting ground. He began by scraping his own teeth, which looked white and clean to the naked eye. Under the microscope, he observed “a little white matter” that appeared “about as thick as batter.” Within that plaque Leeuwenhoek saw countless tiny animals “which moved very prettily.” Some of the creatures shot along “like a pike through the water.” This was a momentous find, one of the first observations of living bacteria.

  Leeuwenhoek delighted in showing such wonders to visitors, though some winced while their host beamed. One nervous group rinsed their mouths with vinegar and several rounds of water, to make certain that Leeuwenhoek would not find creatures living on their teeth. To no avail, since vinegar itself abounded with tiny, swimming worms. “Some of them were so disgusted at what they saw,” Leeuwenhoek purred, “that they resolved never to take vinegar again.”

  Always happy to launch into a frenzy of arithmetic, Leeuwenhoek started calculating. Despite his own clean habits, he noted, “there are not living in our United Netherlands so many people as I carry living animals in my mouth this very day.” (His estimates of how many creatures he observed, and their tiny dimensions, were remarkably accurate, although they relied on homemade and improvised measuring sticks. Leeuwenhoek gauged the diameter of a fly’s blood vessels, for instance, by comparing them with the number of “divisions [on a brass ruler] that one of the thickest hairs from my beard will cover.”)

  Many of the challenges he took on sound like the labors of Hercules, if Hercules had been the size of Tom Thumb. “I also with much trouble took out the testicles of a flea, and placed them before my microscope,” Leeuwenhoek told the Royal Society. A few sentences later, he noted that “I took also some flesh from the feet of a gnat.” He thrilled at the sight of blood in the capillaries—Leeuwenhoek was the first to see capillaries and the first to see blood cells—and he stared entranced at a spectacle that Harvey had only imagined. In the tiny blood vessels in a tadpole’s tail, Leeuwenhoek saw the blood traveling as clearly “as when, with the naked eye, we see the water leaping high out of a fountain and then falling down again.”

  He wrote with unquenchable excitement, a tour guide who grew ever more enthusiastic as the samples he collected grew less and less enticing. Blackheads intrigued him, and so did earwax and pus and his own diarrhea (where he found “animalcules a-moving very prettily,” with long bodies and flat bellies, and “furnished with sundry little paws”).

  Curious to see what a callus looked like in close-up, Leeuwenhoek stripped off his socks and shoes. Then he placed his foot upon a piece of blue paper and recruited his servant. The hapless man, “partly with his Nails and partly with a Penknife,” managed to pry off a bit of skin. Intrigued with his first glimpse of this “hard Skin,” Leeuwenhoek recruited a mason, then a carpenter, and then a plowman, and sliced skin samples from their work-hardened hands.

  In these early days of science, devout and brilliant thinkers like Kepler, Galileo, and Newton found inspiration in contemplating the starry tapestry that God had flung across the heavens. Antony van Leeuwenhoek, a titan of another stripe, followed a different path. To grasp the magnificence of God’s creation, he fervently believed, one could study not the fiery sun and the stately procession of the planets but pond scum, and spit, and blood, and fleas, and worms.

  ELEVEN

  “ANIMALS OF THE SEMEN”

  ON AN AUTUMN NIGHT IN 1677, LEEUWENHOEK AND HIS WIFE made love. He leapt up “immediately after ejaculation before six beats of the pulse had intervened,” and ran to his microscope with a sample of semen. There Leeuwenhoek saw “so great a number of living animalcules that sometimes more than a thousand were moving about in an amount of material the size of a grain of sand.” He did not tell the Royal Society if Mrs. Leeuwenhoek found this a thrilling discovery.

  This observation would eventually take its place as a towering milestone in the history of science. But Leeuwenhoek, who ordinarily was happy to trumpet his finds, played this one down. He reminded the Royal Society that this had been their idea, not his. With uncharacteristic self-consciousness, he noted that he had obtained his test sample by “conjugal coitus” rather than by “sinfully defiling myself.” He even took the trouble of having his letter translated into Latin, perhaps to shield tender readers. Despite his precautions, Leeuwenhoek wrote, he recognized that his observations might “disgust or scandalize the learned.” He gave the Royal Society permission to publish his letter or burn it, as they saw fit.


  There is no mistaking what Leeuwenhoek saw on that long-ago evening when he dashed out of bed. The tiny creatures under his microscope “were furnished with a thin tail, about five or six times as long as the body.” They corkscrewed along “owing to the motion of their tails like that of a snake or an eel swimming in water,” as if they were racing toward some important destination.

  There is no mistaking what he saw, but Leeuwenhoek did mistake it. Historians hail Leeuwenhoek as the first man to see sperm cells, but that is only partly right. He did see tiny eels swimming in his semen, but he did not suspect that they had anything to do with procreation. Instead, he thought he had found micro-animals that happened to live in semen. After all, hordes of microscopic creatures seemed to cavort everywhere—in drops of water, in tree sap, on your teeth, between your toes. Why shouldn’t semen have creatures of its own?

  For half a dozen years, Leeuwenhoek held to this view. Like Columbus, who “discovered” the new world while insisting that he had found the Indies, Leeuwenhoek vehemently misunderstood his own discovery. And just as Columbus immortalized his error in the name “Indians,” so Leeuwenhoek called sperm cells “little animals.”

  Most scientists agreed with him. Odder still, they continued to believe that sperm cells were tiny animals that had nothing to do with sex or reproduction long after Leeuwenhoek himself had changed his mind. A century and a half after Leeuwenhoek first saw sperm cells, well into the 1800s, the animal theory was still conventional wisdom. Meticulous illustrations in biology journals showed carefully drawn sperm cells, with neatly labeled mouths and bladders and other organs, or showed sperm cells and tapeworms side by side, by way of comparing different microscopic animals.

  In 1830, an article in the Lancet, the leading medical journal of the day, included spermatozoa in a discussion of intestinal worms. “Animalcules are always found in the semen, which is, no doubt, their natural habitation,” the Lancet noted. “They cause no inconvenience and, no doubt, serve some important purpose.” Even the word “spermatozoa” reflects this long-lived error. The word was coined in the year 1827 by a scientist who believed that sperm cells were worm-like creatures from the genus Cercariae. “Spermatozoa” means “animals of the semen.”

  FIGURE 11.1. An illustration depicting a variety of parasites, from a medical text written in 1840, shows a sperm cell (at left) along with tapeworms and other unappealing creatures.

  Some scientists found a different way to miss the point of Leeuwenhoek’s discovery. Sperm cells were not little animals; they were stirring rods! This view, too, lasted until the 1800s. The idea was that semen was important but sperm cells were not, except as a means of keeping the semen from stagnating. Biologists looked at semen, just sitting there waiting for the big day, and contrasted it with blood, which was in constant movement. They saw the difference between a river’s vitality and a pond’s torpor. What could be plainer than that Leeuwenhoek’s wriggling, twisting, perpetually swimming animalcules were animated swizzle sticks?

  These were colossal errors. With an essential clue to the babies mystery in their hands, scientists had fumbled it away. It was not only that they had picked up a smoking gun and failed to see what it was. Worse, they had watched the wisps of smoke rise into the air and said, “What a curious teakettle!” and then set the gun aside.

  HOW DID EVERYONE GET IT SO WRONG? PART OF THE PROBLEM was that Leeuwenhoek and his peers had no vocabulary that fit his discovery. Today we talk about cells as the building blocks of life. Cells are to biology what atoms are to chemistry, and the first page of every biology textbook explains that all living organisms are composed of cells. We talk of sperm cells and egg cells as if they are natural features of the living world that no one could miss, like trees and birds. But the cell theory dates from the early 1800s, well over a century after Leeuwenhoek. (I have sometimes referred to “sperm cells” because the term is almost unavoidable, but it is an anachronism.)

  In the 1600s and 1700s, when scientists saw anything little that looked alive, they took for granted that it was some sort of bug or beast or worm. So when Leeuwenhoek looked at semen through his microscope and saw “animalcules” swimming purposefully along—not drifting along like sticks in a stream or floating haphazardly like seaweed but thrashing their tails and racing—he immediately classified them as animals. What else could they be?

  (Eggs, if they had been found first, might not have led to the same wrong turn. Early scientists thought of eggs as immobile and associated them with calm and repose. Sperm cells, with their thrashing tails and vast numbers, called to mind tumult and confusion and, above all, activity. In short, life.)

  Even so, there were problems with the notion of spermatozoa as microtadpoles that happened to have found a pond in the testicles. The biggest riddle was simply put: If these were animals, where had they come from? They had landed in a most unlikely home (“Out of the way location, no central heating, poor views”), and they could hardly have drifted in on the breeze or hitched a ride on a bite of food. Who were these interlopers?

  Eventually this question would take on tremendous importance. In the meantime, it was put aside in favor of more immediate chores, like sorting out whether animalcules turned up in all sorts of male animals and at all stages of life.

  LEEUWENHOEK HIMSELF BELIEVED HE HAD SPOTTED SOMETHING in semen far more significant than tiny, swimming animals. This observation, though in fact it was utterly mistaken, filled him with “wonder” about the mystery of procreation; the sight of his tiny animals, which genuinely was a breakthrough for the ages, had stirred no such thoughts. Within the liquid part of the semen—not inside the swimming animalcules—Leeuwenhoek reported seeing “all manner of great and small vessels.” He had “not the least doubt,” he told the Royal Society in November 1677, “that they are nerves, arteries, and veins.”

  Convinced that he had made a giant find, Leeuwenhoek returned to the same theme in another letter to the Royal Society a few months later. The nerves and blood vessels he had seen, he proposed, somehow gave rise to all the parts in a developing embryo. “It is exclusively the male semen that forms the fetus and all that the woman may contribute only serves to receive the semen and feed it.”

  This was bizarre for several reasons. For one thing, Leeuwenhoek had made a momentous discovery and then ignored it. For another, the vessels that filled him with wonder do not exist, and no one has ever figured out just what it was that this brilliant observer actually saw. Finally, Leeuwenhoek’s assertion that semen was vitally important to conception and that the egg played no role whatever came out of the blue. He dismissed the egg contemptuously but did not bother to provide any arguments to back his claim.

  The secretary of the Royal Society, a physician and botanist named Nehemiah Grew, didn’t buy it. He sent Leeuwenhoek a challenging letter. “Our Harvey and your de Graaf”—the eminent Englishman and the accomplished Dutchman—had proposed a strikingly different picture of conception. Those renowned scientists had focused almost entirely on the egg, Grew reminded Leeuwenhoek. In their view, semen played a distinctly secondary role; it merely started the egg on its path toward development, and it did so in the most airy, ethereal fashion. Semen did not physically contact the egg, wrote Grew, but merely awoke it with “a certain breath” from a discreet distance. How did that picture of an ever-so-gentle air kiss fit with Leeuwenhoek’s confused account of tangled nerves and arteries and swimming eels racing one another?

  Always cantankerous when challenged, Leeuwenhoek lashed out. He informed the Royal Society that he had heard of one author who had cited seventy scientists who echoed Harvey and de Graaf. What of it? If there had been “seventy times seventy more” all chanting in unison, still he would “maintain that every one of them has erred.”

  But Leeuwenhoek did more than sputter in irritation. Spurred by Grew’s challenge, he looked closely at just what de Graaf and Harvey had written about conception. By this roundabout path, finally, he came to recognize the importance of
the tiny animals he had seen swimming in his semen seven years before.

  The crucial experiment came on December 31, 1684. At eight o’clock that morning, and then again at two in the afternoon, Leeuwenhoek watched as a male dog mated with a female in heat. Then he had the female killed (with an awl thrust into her spine) and cut open. With his naked eye, he saw no sign of semen. So far this was exactly what Harvey and de Graaf had reported. (From our vantage point, the failure to find semen makes sense. Semen would have been nearly impossible to see because it would have dispersed in the wet mess of a freshly opened body.)

  Now Leeuwenhoek looked through his microscope. Neither Harvey nor de Graaf had done such a thing. “I discovered to my great satisfaction an abundance of living animalcules, these being the male seed of the dog,” he wrote triumphantly. The number of tiny animals was so huge that “in my estimation an odd hundred million or so would make little difference to the reckoning.”

  Leeuwenhoek had earlier proclaimed what he believed was the true story of conception. At the time he’d had no proof. Now, he felt, he had proved his case so decisively that only the “obstinately opinionated” could deny it. The dog he had cut open was not the point; the dog was the arrow that showed the way to a general truth. “A human being originates not from an egg but from an animalcule that is found in male sperm.”

  From the start, Leeuwenhoek had hailed semen as all-important. That did not change. What was new here was that Leeuwenhoek had moved the spotlight. Now he made no mention of the mysterious “vessels” and nerves that had once struck him as the key to the procreation riddle. Instead, he focused on the millions upon millions of tiny, swimming animals within the semen. Do you see? Look there! The secret of life lay hidden within those microscopic, wriggling bodies.