Leeuwenhoek and sperm cells

A quote from The Clockwork Universe: Isaac Newton, the Royal Society, and the Birth of the Modern World by Edward Dolnick

‘Leeuwenhoek jumped up from his bed one night, “immediately after ejaculation before six beats of the pulse had intervened,” and raced to his microscope. There he became the first person ever to see sperm cells. “More than a thousand were moving about in an amount of material the size of a grain of sand,” he wrote in amazement, and “they were furnished with a thin tail, about five or six times as long as the body . . . and moved forward owing to the motion of their tails like that of a snake or an eel swimming in water.” Leeuwenhoek hastened to assure the Royal Society that he had obtained his sample “after conjugal coitus” (rather than “by sinfully defiling myself”), but he did not discuss whether Mrs. Leeuwenhoek shared his fascination with scientific observation.’