September 17 - Anton van Leeuwenhoek and bacteria

On September 17, 1683, Dutch merchant and early scientist Anton van Leeuwenhoek wrote to the Royal Society of England describing and illustrating five different kinds of objects, which he called “animalcules,” he had found in his own saliva and plaque. The father of microscopy had discovered bacteria. As a tradesman in Delft, he had used magnifying glasses to count threads in cloth, which led to his interest in lensmaking, accomplished in secret by processing thin rods of glass into very small spheres offering high magnification (more than 200x). His “microscopes” consisted of a brass plate a few inches long, with the lens in a tiny hole (pictured). Though he had first observed microscopic life in 1674, his letter of 1683 reported with “great wonder … many very little living animalcules, very prettily a-moving.” He also described “enormous numbers” of animalcules from the mouths of two old men who had never cleaned their teeth in their lives. In hundreds of other letters, Van Leeuwenhoek also described the life in a drop of water and blood corpuscles circulating in capillaries.