LEUWENHOEK or LEEUWENHOEK, ANTHONY VAN, was born at Delft in Holland in 1632, and does not seem to have had the advantage of a learned education. The skill which he possessed in grindiug glasses for microscopes first brought him into notice, and his microscopes were said even to excel those of the celebrated Eustachio Divini. He did not confine his attention however to the mechanical construction of instruments, but made many researches on the minute structure and composition of various animal fluids and solid textures, and he acquired great fame as an anatomist and physio logist. Dr.De Graaf introduced him to the notice of the Royal Society of London, and the greater number of his discoveries and researches were published in the 'Philosophical Transactions' of that body. His first communication was traosmitted to the Royal Society by DH Graaf in 1673. His contributions to the ' Philosophical Transactions' became afterwards numerous and important, and amounted altogether to about 112 papers, which are included between No. 94 and No. 380 of that work. In 1680 he was chosen a Fellow of the Royal Society, and he was made a corresponding member of the Academy of Sciences at Paris in 1697. He appears to have passed the whole of his life at his native place, devoting his time to microscopic researches, chiefly relating to anatomy ; and the success which attended his observatious is said to have principally arisen from his having paid the most minute attention to the grinding and polishing of single lenses, which he always used in preference to the compound microscope.
The subjects of Leuwenhoek's labours were so numerous, that we can only briefly mention some of the moat important of them. Some of the antagonists of Harvey objected to his doctrine of the circulation of the blood on the ground that, if the blood passed directly from the arteries into the veins, it could not nourish the parts through which it flowed. This question was undecided, when Leuweuhoek commu nicated a memoir to the Royal Society, in which he stated, as the result of his experiments, that, contrary to the opinion of Harvey, the passage of the blood was not immediate from the arteries into the veins. However in 1690, having very carefully re-examined the courao
of the circulation through the minute vessels of a part with a more perfect microscope, he discovered and clearly demonstrated that tho arteries and veins are continuous. He even refused to admit that there is any division between the arterial and venous capillaries, because he said that it is impossible to determine where arteries ter minate or veins begin. The latest investigations have proved the conclusions of this great microscopist to be nearly correct ; for though the transit of the blood from arteries to veins can be observed by means of the microscope in many transparent parts, as the web of the frog's foot, yet the nature of the minute or capillary vessels through which the communication is effected is imperfectly understood.
At the time when Leuwenhoek made these observations the chemical doctrines reigned in medicine, and all the processes in the animal economy were explained by chemical changes : the blood was said to undergo the process of fermentation. Leuwenhoek triumphantly opposed this hypothesis, objecting to it that, if fermentation took place, bubbles of air would be generated in the vessels, which could never be observed. He also directed his attention to the form of the globules of the blood, which Malpighi had already discovered. Leuwenhoek stated that they are oval and flattened, and that each is composed of six exceedingly minute conical particles, which separately do not reflect the red colour, but which by their union communicate to the blood the physical properties which it presents. This theory served as the basis of that of Boerhaave on inflammation. Leuwenhoek stated, in proof of his hypothesis, that the red capillary vessels divide into smaller branches, in which the circulation is beyond the influence of the heart, and where the blood appears white because its globules are divided so as to accommodate themselves to the size of the canals through which they pass. Later experiments have shown the fallacy of these ideas on the blood.