Van Leeuwenhoek's curiosity was insatiable, and he examined everything he could with
his microscopes, ranging from samples of about 200 biological species to mineral
objects; he even attempted to observe the explosion of gunpowder.
Van Leeuwenhoek gave clearer descriptions of red blood cells than either of his
contemporaries Marcello Malpighi and Jan Swammerdam. He first described them in 1674
and estimated their size to be, in modern terminology, 8.5 microns in diameter (the
correct value is 7.7 microns). In 1682 he clearly described the nucleus within the red
blood cells of fish, and in 1683 he noticed the sedimentation of erythrocytes from a
suspension and their lysis upon addition of water. His description of the blood capillaries
in the intestine in 1683 was accompanied by comments on a different type of capillary
which contained "a white fluid, like milk"; he had discovered the lymphatic capillaries.
In 1677 van Leeuwenhoek examined fresh semen, in which he observed living
spermatozoa. His unique observations on microorganisms probably began in 1674, when
he examined water from a lake near Delft. He gave the first description of the common
green alga Spirogyra but also observed smaller organisms, which were probably
free-living protozoa. Dobell believed that van Leeuwenhoek saw Vorticella, Monas, Bodo
caudatus, and Colpidium.
Van Leeuwenhoek also discovered parasitic protozoa, describing the flagellate Giardia in
a sample of his feces, which also contained bacteria which can be identified as
Spirochaeta. In a letter written in 1683 he describes and illustrates five different kinds of
bacteria present in his own mouth: these can readily be identified as a motile bacillus,
Selenomonas sputigena, a micrococcus, Leptothrix buccalis, and a spirochete. He continued
to make observations on microorganisms until 1716, and while studying free-living
protozoa, he also discovered other organisms such as Volvox, Hydra, and rotifers.
Van Leeuwenhoek's discovery of microorganisms has tended to overshadow his other
work, which has not received full recognition. He was one of the first comparative
anatomists, since he often followed a structure in several different species. As a pioneer
of microdissection, he succeeded in obtaining results which are remarkable even by
modern standards. Between 1680 and 1701 he carried out a series of microdissections,
mainly on insects, and one of his most original discoveries was parthenogenesis in
aphids. The parent aphids did not contain eggs, but young aphids just like the parent.
Van Leeuwenhoek's insatiable curiosity, coupled with remarkable tenacity and skill,
makes him one of the most outstanding scientists of all time. In his own modest way he
realized how rare his gifts were and also that other people's motives were not always
those of a true student of nature. In a 1715 letter he noted: "Some go to make money
out of science, or to get a reputation in the learned world. But in lens-grinding and
discovering things hidden from our sight, these count for nought. And I am satisfied too
that not one man in a thousand is capable of such study, because it needs much time ...
and you must always keep thinking about these things if you are to get any results. And
over and above all, most men are not curious to know: nay, some even make no bones
about saying, What does it matter whether we know this or not?"
Became Fellow of the Royal Society, 1680.
- THE COLLECTED LETTERS OF ANTONI VAN LEEUWENHOEK was edited by a committee of Dutch scientists (8 vols., 1939-1967). A work on van Leeuwenhoek and His Clifford Dobell, ANTONY VAN LEEUWENHOEK AND HIS LITTLE ANIMALS (1932). See also Abraham Schierbeek, MEASURING THE INVISIBLE WORLD (1959).