Leeuwenhoek, Antony van
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Leeuwenhoek, detail of a portrait by Jan Verkolje;
in the Rijksmuseum, Amsterdam |
(b. Oct. 24, 1632, Delft, Neth.--d. Aug. 26, 1723, Delft), Dutch microscopist
who was the first to observe bacteria and protozoa. His researches on lower
animals refuted the doctrine of spontaneous generation, and his observations
helped lay the foundations for the sciences of bacteriology and protozoology.
(see also Index: microbiology)
Little is known of Leeuwenhoek's early life. When his stepfather
died in 1648, he was sent to Amsterdam to become an apprentice to a linendraper.
Returning to Delft when he was 20, he established himself as a draper and
haberdasher. In 1660 he obtained a position as chamberlain to the sheriffs
of Delft. His income was thus secure and sufficient enough to enable him
to devote much of his time to his all-absorbing hobby, that of grinding
lenses and using them to study tiny objects.
Leeuwenhoek made microscopes consisting of a single, high-quality
lens of very short focal length; at the time, such simple microscopes were
preferable to the compound microscope, which increased the problem of chromatic
aberration. Although Leeuwenhoek's studies lacked the organization
of formal scientific research, his powers of careful observation enabled
him to make discoveries of fundamental importance. In 1674 he began to
observe bacteria and protozoa, his "very little animalcules," which he
was able to isolate from different sources, such as rainwater, pond and
well water, and the human mouth and intestine, and he calculated their
sizes.
In 1677 he described for the first time the spermatozoa from insects,
dogs, and man, though Stephen Hamm probably was a codiscoverer. Leeuwenhoek
studied the structure of the optic lens, striations in muscles, the
mouthparts of insects, and the fine structure of plants and discovered
parthenogenesis in aphids. In 1680 he noticed that yeasts consist of minute
globular particles. He extended Marcello Malpighi's demonstration in 1660
of the blood capillaries by giving (in 1684) the first accurate description
of red blood cells. In his observations on rotifers in 1702, Leeuwenhoek
remarked that "in all falling rain, carried from gutters into water-butts,
animalcules are to be found; and that in all kinds of water, standing in
the open air, animalcules can turn up. For these animalcules can be carried
over by the wind, along with the bits of dust floating in the air."
A friend of Leeuwenhoek put him in touch with the Royal Society
of England, to which, from 1673 until 1723, he communicated by means of
informal letters most of his discoveries and to which he was elected a
fellow in 1680. His discoveries were for the most part made public in the
society's Philosophical Transactions. The first representation of
bacteria is to be found in a drawing by Leeuwenhoek in that publication
in 1683.
His researches on the life histories of various low forms of animal
life were in opposition to the doctrine that they could be produced spontaneously
or bred from corruption. Thus, he showed that the weevils of granaries
(in his time commonly supposed to be bred from wheat as well as in it)
are really grubs hatched from eggs deposited by winged insects. His letter
on the flea, in which he not only described its structure but traced out
the whole history of its metamorphosis, is of great interest, not so much
for the exactness of his observations as for an illustration of his opposition
to the spontaneous generation of many lower organisms, such as "this minute
and despised creature." Some theorists asserted that the flea was produced
from sand, others from dust or the like, but Leeuwenhoek proved
that it bred in the regular way of winged insects.
Leeuwenhoek also carefully studied the history of the ant and
was the first to show that what had been commonly reputed to be ants' eggs
were really their pupae, containing the perfect insect nearly ready for
emergence, and that the true eggs were much smaller and gave origin to
maggots, or larvae. He argued that the sea mussel and other shellfish were
not generated out of sand found at the seashore or mud in the beds of rivers
at low water but from spawn, by the regular course of generation. He maintained
the same to be true of the freshwater mussel, whose embryos he examined
so carefully that he was able to observe how they were consumed by "animalcules,"
many of which, according to his description, must have included ciliates
in conjugation, flagellates, and the Vorticella. Similarly, he investigated
the generation of eels, which were at that time supposed to be produced
from dew without the ordinary process of generation.
The dramatic nature of his discoveries made him world famous, and he
was visited by many notables--including Peter I the Great of Russia, James
II of England, and Frederick II the Great of Prussia.
Leeuwenhoek's methods of microscopy, which he kept secret, remain
something of a mystery. During his lifetime he ground more than 400 lenses,
most of which were very small--some no larger than a pinhead--and usually
mounted them between two thin brass plates, riveted together. A large sample
of these lenses, bequeathed to the Royal Society, were found to have magnifying
powers of between 50 and, at the most, 300 times. In order to observe phenomena
as small as bacteria, Leeuwenhoek must have employed some form of
oblique illumination, or other technique, for enhancing the effectiveness
of the lens, but this method he would not reveal. Leeuwenhoek continued
his work almost to the end of his long life of 90 years.
Leeuwenhoek's contributions to the Philosophical Transactions
amounted to 375 and those to the Memoirs of the Paris Academy of
Sciences to 27. Two collections of his works appeared during his life,
one in Dutch (1685-1718) and the other in Latin (1715-22); a selection
was translated by S. Hoole, The Select Works of A. van Leeuwenhoek
(1798-1807).
BIBLIOGRAPHY.
Clifford Dobell, Antony van Leeuwenhoek and His "Little Animals"
(1932, reissued 1960); and Brian J. Ford, Single Lens: The Story
of the Simple Microscope (1985).
Copyright 1994-1998 Encyclopaedia Britannica
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