An abstract of a letter…Sep. 17, 1683. Containing some microscopical observations, about animals in the scurf of the teeth.

Records discovery of bacteria in the mouth, with the first illustrations of the basic types – what were much later called cocci (round or oval), bacilli (rod-shaped) and spiriillum (spiral) forms. Although Leeuwenhoek had observed bacteria earlier, calling them animalcules, this paper is usually considered the first memoir on what were later called bacteria. At this early date the concept of microbiome did not yet exist; however, this paper also marks the beginning of our understanding of how parts of the human body are normally populated by bacteria. Digital facsimile from the Royal Society at this link.