Anton Philips van Leeuwenhoek (born on October 24, 1632 – baptized on November 4, and buried on August 30, 1723) was a Dutch tradesman and scientist from Delft, the Netherlands. He is commonly known as "the Father of Microbiology", and considered to be the first microbiologist. He is best known for his work on the improvement of the microscope and for his contributions towards the establishment of microbiology. Using his handcrafted microscopes he was the first to observe and describe single celled organisms, which he originally referred to as animalcules, and which we now refer to as microorganisms. He was also the first to record microscopic observations of muscle fibers, bacteria, spermatozoa and blood flow in capillaries (small blood vessels). Van Leeuwenhoek never wrote a book, just letters.