Leeuwenhoek, Or Leeuwenhoeek, Antonins Tan, a Dutch naturalist, born in Delft, Oct. 24, 1632, died there, Aug. 26, 1723. He had no learned education, and in early life was engaged in mercantile pursuits. He cultivated science during his spare moments, and attained the reputation of making the best microscopes in Europe. By his applications of the microscope, and by the researches in physiology to which they conducted him, he attracted the attention of the royal society of London; and the greater part of his writings, containing accounts of his discoveries, were published in the English " Philosophical Transactions." He was among the first observers to employ the microscope in anatomical and physiological investigations, of which he made a great number by means of simple microscopes of his own construction. These instruments consisted of a single biconvex lens, fixed in a perforated metallic plate, to which was attached a movable needle destined to carry and fix in a proper position the object to be examined. Though of such simple construction, they were often of very high magnifying power, owing to the strong convexity of the surfaces of the lens.

Leeuwenhoek was particularly distinguished for his discovery of the red globules of the blood in 1673, that of the infusorial animalcules in 1675, and that of the spermatozoa in 1677. Malpighi had seen and mentioned as early as 1661 what were undoubtedly the blood globules; but he did not perceive their true nature nor give an exact description of them. Leeuwenhoek discovered their existence and their most important characters in human blood as well as in that of birds, reptiles, and fishes. The spermatozoa were first seen by a student of medicine named Ham. He immediately communicated the fact to Leeuwenhoek, who at once verified the reality of the discovery in the human spermatic fluid, and extended it to that of the dog, the rabbit, the ram, the cock, and various other animals. The infusorial animalcules he discovered in the rain water which ran from the roof of his house. Leeu-wenhoek's life was passed in scientific research and in manufacturing optical instruments in his native city. He was visited by Queen Mary, and was invited to visit the czar Peter when that sovereign was in Delft. His writings were collected and published in Dutch separately at Delft and Leyden. They also appeared in Latin (Delft, 1695), and a selection of his works, containing his microscopical discoveries in many departments of nature, translated into English by Samuel Hoole, was published in London, 1798-1801.