He is best known for his contribution to improvement of the microscope and his contributions towards the establishment of cell biology.
Using his handcrafted microscope he observed muscles fibres, bacteria, spermatozoa and blood flow in capillaries? (small [blood vessel]?s).
During his lifetime van Leeuwenhoek carved over 500 optical lenses .
He is thought to have been be the model for Vermeer?'s painting The Geographer; the two were close friends.