LEEUWENHOEK, or LEUWENHOEK, ANTHONY VAN (1632- 1723), Dutch microscopist, was born at Delft on the 24th of October 1632. For a short time he was in a merchant's office in Amsterdam, but early devoted himself to the manufacture of microscopes and to the study of the minute structure of organized bodies by their aid. He appears soon to have found that single lenses of very short focus were preferable to the compound microscopes then in use; and it is clear from the discoveries he made with these that they must have been of very excellent quality. His discoveries were for the most part made public in the Philosophical Transactions of the Royal Society, to the notice of which body he was introduced by R. de Graaf in 1673, and of which he was elected a fellow in 1680. He was chosen a corresponding member of the Paris Academy of Sciences in 1697. He died at his native place on the 26th of August 1723. Though his researches were not conducted on any definite scientific plan, his powers of careful observation enabled him to make many interesting discoveries in the minute anatomy of man, the higher animals and insects. He confirmed and extended M. Malpighi's demonstration of the blood capillaries in 1668, and six years later he gave the first accurate description of the red blood corpuscles, which he found to be circular in man but oval in frogs and fishes. In 1677 he described and illustrated the spermatozoa in dogs and other animals, though in this discovery Stephen Hamm had anticipated him by a few months; and he investigated the structure of the teeth, crystalline lens, muscle, etc. In 1680 he noticed that yeast consists of minute globular particles, and he described the different structure of the stem in monocotyledonous and dicotyledonous plants.
His researches in the life-history of various of the lower 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 grubs hatched from eggs deposited by winged insects. His chapter on the flea, in which he not only describes its structure, but traces out the whole history of its metamorphoses from its first emergence from the egg, is full of interest not so much for the exactness of his observations, as for its incidental revelation of the extraordinary ignorance then prevalent in regard to the origin and propagation of " this minute and despised creature," which some asserted to be produced from sand, others from dust, others from the dung of pigeons, and others from urine, but which he showed to be " endowed with as great perfection in its kind as any large animal," and proved to breed in the regular way of winged insects. He even noted the fact that the pupa of the flea is sometimes attacked and fed upon by a mite an observation which suggested the well known lines of Swift. His attention having been drawn to the blighting of the young shoots of fruit-trees, which was commonly attributed to the ants found upon them, he was the first to find the Aphides that really do the mischief; and, upon searching into the history of their generation, he observed the young within the bodies of their parents. He carefully studied also the history of the ant and was the first to show that what had been commonly reputed to be " ants' eggs " are really their pupae, containing the perfect insect nearly ready for emersion, whilst the true eggs are far smaller, and give origin to " maggots " or larvae. Of the sea-mussel, again, and other shell-fish, he argued (in reply to a then recent defence of Aristotle's doctrine by F. Buonanni, a learned Jesuit of Rome) that they are not generated out of the mud or sand found on the seashore or the beds of rivers at low water, but from spawn, by the regular course of generation; and he maintained the same to be true of the fresh-water mussel (Unio), whose ova he examined so carefully that he saw in them the rotation of the embryo, a phenomenon supposed to have been first discovered long afterwards. In the same spirit he investigated the generation of eels, which were at that time supposed, not only by the ignorant vulgar, but by " respectable and learned men," to be produced from dew without the ordinary process of generation. Not only was he the first discoverer of the rotifers, but he showed " how wonderfully nature has provided for the preservation of their species," by their tolerance of the drying-up of the water they inhabit, and the resistance afforded to the evaporation of the fluids of their bodies by the impermeability of the casing in which they then become enclosed. " We can now easily conceive," he says, " that in all rain-water which is collected from gutters in cisterns, and in all waters exposed to the air, animalcules may be found ; for they may be carried thither by the particles of dust blown about by the winds."
Leeuwenhoek's contributions to the Philosophical Transactions amounted to one hundred and twelve; he also published twenty-six papers in the Memoirs of the Paris Academy of Sciences. Two collections of his works appeared during his life, one in Dutch (Leiden and Delft, 1685-1718), and the Bother in Latin (Opera omnia s. Arcana naturae ope exactissimorum microscopiorum selecta, Leiden, I 7 I 5~i7 22 ); and a selection from them was translated by S. Hoole and published in English (London, 1798-1781).
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)