Leeuwenhoek

LEEUWENHOEK Antoni (Antoni van Leeuwenhoek, 1632-1723), famous Dutch microscopist and naturalist of the second half of the 17th and early 18th centuries. Together with Malpighi, he is one of the founders of scientific microscopy, microscopic anatomy, zoology, and botany. It can be stated that he laid the foundation of modern protistology. He was born and died in the city of Delft. Initially, he engaged in trade. He took up microscopy as an amateur, preparing himself very good and strongly magnifying short-focus lenses. He conducted his microscopic observations without a definite scientific plan; however, possessing exceptional observational abilities and apparently quickly orienting himself in the evaluation of biological objects, he made a series of discoveries of primary importance in the field of microscopic morphology. He is credited with the discovery and detailed description of erythrocytes—round in humans, oval in frogs and fish (1674), the transverse striation of muscles, the structure of the tooth, lens, and compound eye of insects. In 1677, he gave a description and drawings of dog spermatozoa and those of other animals, although in this respect he was preceded by a few months by his student Ham (Ludwig von Ham) of Stettin. In the field of zoology, L. discovered rotifers, budding of hydras, and the asexual reproduction of aphids (Aphidae). In the field of protistology, L. actually discovered infusorians (Vorticella) (1675), giving a correct description of their ciliary covering (1677); he was also the first to observe their conjugation process (1675). L. also described shelled rhizopods (Polystomella). Among parasitic protozoa, he discovered the oocysts of coccidia in the rabbit's liver and the flagellate Giardia (Lamblia) in human intestinal contents (1681). Of Leuwenhoek's theoretical views, it is necessary to note that, upon discovering spermatozoa, he inclined toward animalculism, considering the spermatozoon a preformed embryo and the egg merely nourishing material for it. The essential element of L.'s worldview was his most decisive opposition to the doctrine of spontaneous generation: he was the first to prove that the larvae of the grain weevil develop not from grain but from eggs laid by winged insects. In his excellent treatise on the natural history of the flea, he described not only its morphology but also the complete course of its development, proving contrary to the prevailing opinion that these 'smallest and most contemptible creatures' do not arise from dust, manure, urine, etc., but that they 'are endowed with the same degree of perfection as the largest animal,' developing from eggs like winged insects. In his dispute with the Jesuit Buon-nani, who defended Aristotle's view of the generation of marine mollusks and crustaceans from mud, he proved their development from roe. To confirm this, L. succeeded in finding a moving embryo inside the eggshell of a freshwater mollusk Unio. In the same way, L. rebelled against the very common notion of the development of eels from dew. One of the deepest discoveries from a modern point of view was L.'s elucidation of the remarkable adaptation of rotifers that serves to preserve their species, namely their endurance to drying. From this, L. drew a brilliant conclusion that served a heavy blow to all theories of spontaneous generation and is fully worthy of modern epidemiology. He wrote: 'Now we can easily understand how small animals are bred in collections of rainwater in cisterns and generally in all open vessels, for they are carried here by the wind along with the smallest particles of dust.' L. made a discovery of primary importance in the field of botany, clarifying the differences in the structure of mono- and dicotyledonous plants, discovering the existence of spiral vessels in plant parenchyma and other histological details. Biographers of L. note that, being essentially a self-taught amateur and not knowing Latin, the scholarly language of the time, he worked quite independently and, without having a systematic school behind him, sometimes fell into strange errors. However, thanks to his exceptional talent, combined with a great gift of observation and exceptional conscientiousness and diligence, L. immortalized his name in science. L.'s works are collected in Latin in 7 volumes 'Opera omnia sive Arcana naturae ope exactissimorum microscopiorum detecta' (Lugdunum, 1715-1722; abbreviated English edition in 2 volumes, London, 1798-1801).