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                     Antony van Leeuwenhoek (1632-1723)


     . . . my work, which I've done for a long time, was not pursued in
      order to gain the praise I now enjoy, but chiefly from a craving
       after knowledge, which I notice resides in me more than in most
          other men. And therewithal, whenever I found out anything
      remarkable, I have thought it my duty to put down my discovery on
       paper, so that all ingenious people might be informed thereof.

                 Antony van Leeuwenhoek. Letter of June 12, 1716

Antony van Leeuwenhoek was an unlikely scientist. A tradesman of Delft,
Holland, he came from a family of tradesmen, had no fortune, received no
higher education or university degrees, and knew no languages other than his
native Dutch. This would have been enough to exclude him from the scientific
community of his time completely. Yet with skill, diligence, an endless
curiosity, and an open mind free of the scientific dogma of his day,
Leeuwenhoek succeeded in making some of the most important discoveries in
the history of biology. It was he who discovered bacteria, free-living and
parasitic microscopic protists, sperm cells, blood cells, microscopic
nematodes and rotifers, and much more. His researches, which were widely
circulated, opened up an entire world of microscopic life to the awareness
of scientists.

Leeuwenhoek was born in Delft on October 24, 1632. (His last name,
incidentally, often is quite troublesome to non-Dutch speakers:
"layu-wen-hook" is a passable English approximation.) His father was a
basket-maker, while his mother's family were brewers. Antony was educated as
a child in a school in the town of Warmond, then lived with his uncle at
Benthuizen; in 1648 he was apprenticed in a linen-draper's shop. Around 1654
he returned to Delft, where he spent the rest of his life. He set himself up
in business as a draper (a fabric merchant); he is also known to have worked
as a surveyor, a wine assayer, and as a minor city official. In 1676 he
served as the trustee of the estate of the deceased and bankrupt Jan
Vermeer, the famous painter, who had had been born in the same year as
Leeuwenhoek and is thought to have been a friend of his. And at some time
before 1668, Antony van Leeuwenhoek learned to grind lenses, made simple
microscopes, and began observing with them. He seems to have been inspired
to take up microscopy by having seen a copy of Robert Hooke's illustrated
book Micrographia, which depicted Hooke's own observations with the
microscope and was very popular.

             Leeuwenhoek is known to have made over 500 "microscopes," of
             which fewer than ten have survived to the present day. In basic
design, probably all of Leeuwenhoek's instruments -- certainly all the ones
that are known -- were simply powerful magnifying glasses, not compound
microscopes of the type used today. A drawing of one of Leeuwenhoek's
"microscopes" is shown at the left. Compared to modern microscopes, it is an
extremely simple device, using only one lens, mounted in a tiny hole in the
brass plate that makes up the body of the instrument. The specimen was
mounted on the sharp point that sticks up in front of the lens, and its
position and focus could be adjusted by turning the two screws. The entire
instrument was only 3-4 inches long, and had to be held up close to the eye;
it required good lighting and great patience to use.

Compound microscopes (that is, microscopes using more than one lens) had
been invented around 1595, nearly forty years before Leeuwenhoek was born.
Several of Leeuwenhoek's predecessors and contemporaries, notably Robert
Hooke in England and Jan Swammerdam in the Netherlands, had built compound
microscopes and were making important discoveries with them. These were much
more similar to the microscopes in use today. Thus, although Leeuwenhoek is
sometimes called "the inventor of the microscope," he was no such thing.

However, because of various technical difficulties in building them, early
compound microscopes were not practical for magnifying objects more than
about twenty or thirty times natural size. Leeuwenhoek's skill at grinding
lenses, together with his naturally acute eyesight and great care in
adjusting the lighting where he worked, enabled him to build microscopes
that magnified over 200 times, with clearer and brighter images than any of
his colleagues could achieve. What further distinguished him was his
curiosity to observe almost anything that could be placed under his lenses,
and his care in describing what he saw. Although he himself could not draw
well, he hired an illustrator to prepare drawings of the things he saw, to
accompany his written descriptions. Most of his descriptions of
microorganisms are instantly recognizable.

In 1673, Leeuwenhoek began writing letters to the newly-formed Royal Society
of London, describing what he had seen with his microscopes -- his first
letter contained some observations on the stings of bees. For the next fifty
years he corresponded with the Royal Society; his letters, written in Dutch,
were translated into English or Latin and printed in the Philosophical
Transactions of the Royal Society, and often reprinted separately. To give
some of the flavor of his discoveries, we present extracts from his
observations, together with modern pictures of the organisms that
Leeuwenhoek saw.

        In a letter of September 7, 1674, Leeuwenhoek described
        observations on lake water, including an excellent description of
the green charophyte alga Spirogyra: "Passing just lately over this lake, .
. . and examining this water next day, I found floating therein divers
earthy particles, and some green streaks, spirally wound serpent-wise, and
orderly arranged, after the manner of the copper or tin worms, which
distillers use to cool their liquors as they distil over. The whole
circumference of each of these streaks was about the thickness of a hair of
one's head. . . all consisted of very small green globules joined together:
and there were very many small green globules as well."

        A letter dated December 25, 1702, gives descriptions of many
        protists, including this ciliate, Vorticella: "In structure these
little animals were fashioned like a bell, and at the round opening they
made such a stir, that the particles in the water thereabout were set in
motion thereby. . . And though I must have seen quite 20 of these little
animals on their long tails alongside one another very gently moving, with
outstretched bodies and straightened-out tails; yet in an instant, as it
were, they pulled their bodies and their tails together, and no sooner had
they contracted their bodies and tails, than they began to stick their tails
out again very leisurely, and stayed thus some time continuing their gentle
motion: which sight I found mightily diverting."

On September 17, 1683, Leeuwenhoek wrote to the Royal Society about his
observations on the plaque between his own teeth, "a little white matter,
which is as thick as if 'twere batter." He repeated these observations on
two ladies (probably his own wife and daughter), and on two old men who had
never cleaned their teeth in their lives. Looking at these samples with his
microscope, Leeuwenhoek reported how in his own mouth: "I then most always
saw, with great wonder, that in the said matter there were many very little
living animalcules, very prettily a-moving. The biggest sort. . . had a very
strong and swift motion, and shot through the water (or spittle) like a pike
does through the water. The second sort. . . oft-times spun round like a
top. . . and these were far more in number." In the mouth of one of the old
men, Leeuwenhoek found "an unbelievably great company of living animalcules,
a-swimming more nimbly than any I had ever seen up to this time. The biggest
sort. . . bent their body into curves in going forwards. . . Moreover, the
other animalcules were in such enormous numbers, that all the water. . .
seemed to be alive." These were among the first observations on living
bacteria ever recorded.

Leeuwenhoek looked at animal and plant tissues, at mineral crystals and at
fossils. He was the first to see microscopic foraminifera, which he
described as "little cockles. . . no bigger than a coarse sand-grain." He
discovered blood cells, and was the first to see living sperm cells of
animals. He discovered microscopic animals such as nematodes and rotifers.
The list of his discoveries goes on and on. Leeuwenhoek soon became famous
as his letters were published and translated. In 1680 he was elected a full
member of the Royal Society, joining Robert Hooke, Henry Oldenburg, Robert
Boyle, Christopher Wren, and other scientific luminaries of his day --
although he never attended a meeting. In 1698 he demonstrated circulation in
the capillaries of an eel to Tsar Peter the Great of Russia, and he
continued to receive visitors curious to see the strange things he was
describing. He continued his observations until the last days of his life.
After his death on August 30, 1723, the pastor of the New Church at Delft
wrote to the Royal Society:

     . . . Antony van Leeuwenhoek considered that what is true in
     natural philosophy can be most fruitfully investigated by the
     experimental method, supported by the evidence of the senses; for
     which reason, by diligence and tireless labour he made with his
     own hand certain most excellent lenses, with the aid of which he
     discovered many secrets of Nature, now famous throughout the whole
     philosophical World.

British scientist Brian J. Ford has rediscovered some of Leeuwenhoek's
original specimens in the archives of the Royal Society of London. His study
of these historic specimens and other material, using Leeuwenhoek's own
microscopes and other single-lens microscopes, has shown how remarkably good
a scientist and craftsman Leeuwenhoek really was. Here's the full story of
Dr. Ford's research. You might also like to visit the History of the Light
Microscope pages for a great deal of information on microscopes of
Leeuwenhoek's time and afterwards. They're part of the excellent Scientific
and Medical Antique Collecting Guide.

This additional biography of Leeuwenhoek is maintained in Korea.

Berkeley, California resident Al Shinn manufactures replicas of Leeuwenhoek
microscopes. He has also made plans and instructions available, for those
who would like to make their own Leeuwenhoek-type microscopes.