The difficulty with replicating Leeuwenhoek’s observations would become a recurring theme in the correspondence between Leeuwenhoek and the Royal Society. The trouble was due partly to his exceptional skill at preparing and observing specimens—a skill other observers did not share—as well as his unwillingness to divulge his exact methods. But the real problem was the novelty of his microscopical investigations. Others before had magnified the visible and seen previously unseen parts of tiny organisms and artifacts around us. But Leeuwenhoek had begun to surpass what others had done: he was going deeper, and seeing more, than anyone else had seen. His tiny speck of glass in a postage stamp–size bit of brass was becoming a doorway through which he glimpsed a new world.
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The existence of this new world was announced in a letter Leewenhoek wrote to the Royal Society on September 7, 1674. But rather than being heralded with fanfare and self-congratulations, Leeuwenhoek’s most astounding discovery was buried at the end of a twenty-six-page missive. Leeuwenhoek began the letter by describing his observations of the eyeball of a cow, which, like many of his specimens, he obtained from a butcher at the vleeshal across the Hippolytusbuurt. He had pierced the cornea of the cow’s eye with a pin and examined the aqueous humor, the fluid that came out of the eye. He cut the crystalline lens—the cornea—into small pieces and affixed them to the pins of two microscopes. He reported that Swammerdam visited him twice during his examinations to observe the lens himself.
Leeuwenhoek also related that he communicated his observations to his neighbor ’s Gravesande, who informed him of an ancient debate about the optic nerve: some anatomists had affirmed the optic nerve to be hollow, saying that they themselves had observed the hollowness, and that the “animal spirits” conveying the “visible species”—what is seen by the eye—pass through the nerve to the brain. “I thereupon concluded with myself,” Leeuwenhoek explained, “that, if there were such a cavity visible in that Nerve, that it might also be seen by me.” To test this, he obtained three optic nerves of cows, again from the same helpful butcher, and viewed them with his instruments. “I could find no hollowness in them,” Leeuwenhoek reported. Rather, “they were made up of many filamentous particles, of a very soft substance.”
So that the fellows of the Royal Society could see for themselves, Leeuwenhoek prepared a specimen for them. He allowed the fleshy tissue to dry out until it hardened. Then, using a shaving razor, he cut slices of the optic nerve. These slices are about one-fifth of a millimeter (200 micrometers) (which was ten times thicker than the sections of plant specimens that he also sent to the Royal Society). We know Leeuwenhoek employed a shaving razor because he reported to the Royal Society that he used one to cut his slices and sections of specimens, noting that he would frequently resharpen it as he cut. Recently Brian Ford, who examined the specimens under an electron microscope, found some red blood cells on a section of elder pith prepared by Leeuwenhoek—suggesting that the blade used to slice it had previously cut Leeuwenhoek while he was shaving with it. The section of optic nerve remains at the Royal Society, still wrapped in its original paper with Leeuwenhoek’s handwritten label.
After describing his observations of the cow’s optic nerve, Leeuwenhoek passed on to a discussion of his use of a microscope during his visit to the chalk hills in England a few years earlier, and a long discourse on the variation between the different types of chalk and sand he observed there and in Delft.
It is only after twenty or so pages on various topics that Leeuwenhoek disclosed his truly revolutionary discovery. It is no wonder, lying so buried under all the other detailed observations, that his claim seems to have been ignored by the Royal Society fellows—some of whom may not, indeed, have read all the way to the end. About two leagues from Delft, Leeuwenhoek began, there is “an Inland-Sea, called Berkelse-Lake.” In the winter the water is clear, but in the summer it becomes whitish, with small green clouds floating within it. The lake, he noted, abounds with tasty fish. Passing by one day, and noticing the murkiness of the water, he took a sample home with the intention of discovering the cause of the cloudy water. Leeuwenhoek may have expected to see a variety of “globules” floating in the water, giving the lake a murky quality when viewed with the naked eye. But what he observed was different—and would transform the way that people saw the world.
Once he brought the sample of water home, Leeuwenhoek would have gone to his study and closed all the shutters except one, through which a beam of sunlight entered the dark room. He would have put a drop of water into a glass tube affixed to the back of one of his microscopes, lifting the device to his eye in the direction of the sunbeam. Screwing the specimen pin attached to the tube up and down, back and forth, he would have focused the instrument until the initially fuzzy image became clear. What he then saw must have shocked him—it may even have startled him so much that his hand holding the microscope shook. Perhaps he even spilled the water and needed to begin again.
The sight that so rattled Leeuwenhoek was a multiplicity of tiny particles of different shapes (not all of them globular) and sizes and colors. Unbelievably, the little particles were moving—and seemed to be moving themselves, by the use of minuscule legs and fins and hairs. These shapes were, therefore, living beings—living beings that had never even been imagined to exist.
It must have taken some time before Leeuwenhoek regained his composure enough to record his observations. When he did, he described these self-moving particles:
Some of [them] were roundish; those that were somewhat bigger than others, were of an Oval figure: On these latter I saw two legs near the head, and two little fins on the other end of their body.*3 Others were somewhat larger than an Oval, and these were very slow in their motion, and few in number.*4 These little animals [diertgens] had divers colours, some being whitish, others pellucid; others had green and very shining little scales: others again were green in the middle, and before and behind very white,*5 others grayish.
Imagine the shock of realizing, for the first time, that water contains a whole world of living creatures completely invisible to the naked eye. Leeuwenhoek must have looked again at the water without the microscope just to confirm that his eyes alone saw nothing. Then, again with the microscope, through which the invisible animals sprang into view once more. As he described it, “The motion of most of them in the water was so swift, and so various, upwards, downwards, and round about, that I confess I could not but wonder at it.” And wonder at it he did, for hours at a time, until his arms hurt from holding up the microscope and his eyes ached from the effort of seeing through it. Trying to convey to his readers the infinitesimal size of these creatures, Leeuwenhoek estimated that they were, as he put it, “above a thousand times smaller than the smallest ones, which I have hitherto seen in the rind of chees, wheaten flower, mould, and the like.” A thousand times smaller than any previously observed creatures, even creatures observed with a microscope!
In the history of civilization, this discovery must rank high on the list of radical transformations of our view of our world, and our place within it—even higher, perhaps, than Copernicus’s claim that Earth is a planet, like the others, and does not have any special status as the literal center of the universe. What Leeuwenhoek had just realized is that there exists a new world of living beings, a world never before seen, never before even imagined—a world in the water we drink, perhaps even in the food we eat—even, it will turn out, inside our own bodies. This discovery would have profound implications for fields as diverse as medicine, brewing, literature, biology, anatomy, and microscopy. But first, it would have to be noticed, and accepted as true.
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Nothing was said in the meetings or publications of the Royal Society about Leeuwenhoek’s “little animals” following the receipt of this letter. Meanwhile, Leeuwenhoek continued to keep the society apprised of his investigations of bovine optic nerves, red blood corpuscles, salt crystals, tiny (but macroscopic) vinegar eels, the leg of a louse, the
roe of a cod, blood serum, the circulation of sap in an oak leaf, the veins in connective tissue between muscles. Finally, over a year later, on December 20, 1675, he pointedly reminded the fellows, “Last summer I carried out many observations on various waters and discovered in most of them a great many small animals that are incredibly minute.” In his next letter, in January, he further prodded their memories: “I detected living creatures in water, that is ordinary rainwater … that comes up in the sand, and in the water of the canals that run through this town and through the country.” He promised to send more observations about these creatures soon. He kept his pledge in a lengthy letter dated October 9, 1676.
By this time, Leeuwenhoek realized that he needed to be more assertive in his claims. He explained that the creatures he has observed in rainwater are “ten thousand times less [that is, smaller] than those [seen] by Mons. Swamerdam, and by him called Water-fleas or Water-lice, which may be perceived … with the naked eye.” Later in the letter, we find an escalating extravagance of description:
I imagine, that ten hundred thousand of these little Creatures do not equal an ordinary grain of Sand in bigness: And comparing them with a Cheese-mite (which may be seen to move with the naked eye) I make the proportion of one of these small Water-creatures to a Cheese-mite, to be like that of a Bee to a Horse: For, the circumference of one of these little Animals in water, is not so big as the thickness of a hair in a Cheese-mite.
Even the esteemed Swammerdam had observed nothing as small as what he, a simple civil servant, had seen. By comparing the size of the creatures he saw to organic and inorganic objects visible to the naked eye (cheese mites, grains of sand), Leeuwenhoek tried to impart to his readers the incredible smallness of these new creatures. No one was accustomed to thinking in terms of such minuscule measurements. In later years Leeuwenhoek would be viewing creatures he reckoned to be one hundred million and even a billion times smaller than a coarse grain of sand.
Among these animalcules he espied larger and smaller ones: in one sample of rainwater “those very small animalcula did swim gently among one another, moving like as Gnats do in the Air; … these bigger ones, move more swiftly, tumbling round as ’twere, and then making a sudden downfall.” Leeuwenhoek evinced an empathy for some of the creatures, which became tangled up because there were so many of them: “I have seen several hundreds of these poor creatures, within the space of a grain of gross sand, lye fast cluster’d together in a few filaments.”
Not content to examine only rainwater, Leeuwenhoek also examined water from Delft’s canals; full of civic pride, he noted that although he did find animalcules in the canal water, he found far fewer than in the rainwater. The water of the canals was so clean, Leeuwenhoek explained, since the canals were refreshed by water coming in from the river Maas by means of sluices, which was done periodically for the purpose of “conditioning,” or cleaning, the water. He also tested the water of the well in his courtyard. Leeuwenhoek told the Royal Society that his well was surrounded by a high wall, so that sunlight never shone on the water. Leeuwenhoek was surprised at the number of creatures he found swimming within his own drinking water:
This water is in Summer time so cold, that you cannot possibly endure your hand in it for any reasonable time. Not thinking at all to meet with any living creatures in it, (it being of a good taste and clear) looking upon it in Sept. of the last year, I discover’d in it a great number of living animals very small, that were exceeding clear.…
He continued testing the well water for the rest of the year, noting that once winter came, he no longer saw any living animals in it; but he saw “his” animalcules again starting in July.
Even while on vacation, Leeuwenhoek’s observations continued. At the end of July he “went to the Sea-Side, at Schevelingen” (today’s Scheveningen). It was a working vacation, however: “Being on the beach and viewing some of the Sea-water very attentively, I discover’d divers living animals therein.” He gave a man he met on the beach a new glass bottle that he had brought with him for this very purpose. He asked the man to go deep into the water—perhaps Leeuwenhoek could not swim, or perhaps he had a microscope with him and could not leave it on the sand in order to go far into the water himself. He instructed the man to wash the bottle well, “twice or thrice,” and then fill it with the seawater. Leeuwenhoek then “tyed the bottle close with a clean bladder” and observed the water once he returned home shortly afterward. He observed the water daily until August 8, by which time the number of animals had decreased so much as to be “hardly discernible.”
In this long letter, Leeuwenhoek also reported observing animalcules in melted snow. On April 26, he wrote, “I took 2½ ounces of Snow-water, which was about three years old, and which had stood all the time either in my Cellar or Study in a Glass-bottle well stopped.” Apparently the snow had been collected three years earlier, and put into a bottle with an airtight stopper, in order to prevent any possible contamination from the air. This suggests that as early as the winter of 1673, several months before sending his first letter to the Royal Society, Leeuwenhoek had already perceived the possibility of observing little animals in the snow water, and had prepared and put aside snow water for a test of it to be conducted at a later time. Had he already seen little animals even before that time—a good year before his first letter announcing this discovery to the Royal Society? The fact that he put an airtight seal on the bottle to prevent contamination suggests that he knew some water did or might contain little animals. Why had the snow water lain, in its stoppered bottle, for so long before being tested? Was he waiting to develop better microscopes? Or had he just forgotten about it?
He used this three-year-old snow water for an experiment that would lead to another remarkable result: the first unmistakable sighting of bacteria. Leeuwenhoek made an infusion by adding about one-third of an ounce of pepper to water, and allowing it to sit in his study for three weeks. His purpose was to see whether he could learn anything about the cause of the pungent taste of pepper on our tongues—why pepper is so hot to the taste. He may have thought that he would see some Cartesian sharp corpuscles that could tear the tongue. Leeuwenhoek added some of the snow water to this pepper infusion and began observing, keeping detailed notes on what he saw. On April 24, 1676, he saw “an incredible number of very little animals of divers kinds.” One kind of these is clearly bacteria: these animals “were incredibly small, and so small in my eye, that I judged, that if 100 of them lay stretched out one by another, they would not equal the length of a grain of course Sand; and according to this estimate, ten hundred thousand [one million] of them could not equal the dimensions of a grain of such course Sand.”
He continued observing this pepper infusion until the first of June. In May he repeated the experiment, this time with ground peppercorns placed in a teacup with rainwater, which he observed from May 26 until June 12. On June 14, he pounded pepper grains very small and added them to water from his well. He observed this infusion from June 16 until July 20. He also made infusions of ginger, cloves, and nutmeg, again in “porcelain tea-cups.” He tried peppercorns whole, ground to a fine powder, and coarsely ground, and white pepper as well as black pepper. We can imagine his study, its shelves and tables arrayed with stoppered flasks of melted snow, teacups filled with infusions of spices—of pepper, ginger, cloves, and nutmeg—from different dates made with diverse waters, each denoted by labels in his clear but elegant script, so that he would not forget which teacup held which solution.*6 One wonders why he made the infusions in teacups, rather than in glass flasks. Did the use of spices make him think of kitchen crockery? Did he take sips of the infusion over time, to check whether the pungent taste of the pepper and other spices increased or decreased as the infusion steeped, trying to correlate the pungency with the number of little animals? Leeuwenhoek does not say. But he does convey his sense of wonder in what he observed.
For me this was among all the marvels that I have discovered in nature and the most marvellou
s of all, and I must say that, for my part, no more pleasant sight has yet met my eye than this of so many thousands of living creatures in one small drop of water, all huddling and moving, but each creature having his own motion.
On August 2 Leeuwenhoek compared the pepper infusion made with the rainwater to that made with the well water, and found the rainwater specimen clearer, the well water specimen more filled with little animals. He continued his observations until the ninth. Then, in the time-honored tradition of denizens of Europe, Leeuwenhoek went on vacation traveling in Brabant. He continued his observations when he returned on the eighteenth. While he was away, he seems to have missed his “little creatures”; once back, he noted “it was pretty to behold the motion, quivering and trembling all the time.” (Leeuwenhoek’s beloved “little dog, which was much admired by everybody for its long and purely white hair,” died in 1674; these little creatures, seen only by him, seem like substitute pets to Leeuwenhoek. Later he would have a trained parrot.) Throughout, he kept a “diary,” or a scientific log, recording both his observations and his emotions as he made them.
There is yet another revelation in this revolutionary document. Leeuwenhoek described spending time observing “vinegar eels,” known now as Anguillula, nematodes that feed on bacteria in vinegar. Anguillula are about two millimeters long and visible to the naked eye. They were already known to exist and had been observed both with and without microscopes before. But what Leeuwenhoek observed with his microscope was new and astounding. He noticed that the number of eels kept increasing from day to day, even when no new vinegar or water was added, and even while the specimen was kept in a covered flask. He “firmly imagined that the said little eels had thus increased by procreation.” By “pulling asunder” some of the little eels, he saw thin, long particles that he took to be baby eels. He even watched as one of them “which came out first, lay and lived, and wrenched itself loose and remained alive a little while.” This appears to be the first ever observation made on the “viviparity”—the live birth of offspring—in Anguillula. Leeuwenhoek was making his first foray into the study of generation. His next step would be even more astonishing, but that would not come for several more years.
Eye of the Beholder: Johannes Vermeer, Antoni van Leeuwenhoek, and the Reinvention of Seeing Page 29