First really accurate description of the red blood corpuscles, which Swammerdam had noted in 1658.

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.

Leeuwenhoek, one of the first and also one of the greatest of the microbiologists, communicated many of his discoveries to the Royal Society in London. This set is a collection in Dutch of many contributions that van Leeuwenhoek sent to the Royal Society, which were first published in English translation in Philosophical Transactions. Leeuwenhoek was first to describe spermatozoa, and the red blood corpuscles; he discovered the crystalline lens, and was the first to see protozoa under the microscope. He introduced staining in histology in 1719 (saffron for muscle fibers). He also discovered protozoa and bacteria. He is said to have had 250 microscopes and 419 lenses, many of them ground by himself. (See also Nos. 98, 265, 860.) An English translation of his works, omitting all references to spermatozoa, appeared in 2 vols, in 1798-1807. Clifford Dobell’s study, Antony van Leeuwenhoek and his ‘little animals“ (London, 1932), revealed many new facts about the man, and included a bibliography. 

Digital facsimile from loc.gov at this link.

In his letter of 2 March 1717 (letter XXXII) addressed to Abraham van Bleyswyk and first published in this edition, Leewenhoek provided the first morphologic description of nerve fibers accompanied by illustrations. “One of the most interesting features relating to the letter of 2 March 1717 is the accompanying illustration (fig.2, fig 2) for it is probably the first attempt to represent the cross section of a peripheral nerve. Individual nerve fibers can be seen, and the central stroke contained in each is meant to indicate the collapsed central tube, which he assumed was present; or, as we should put it today, the axis cylinder surrounded by the myelin sheath. It seems likely therefore that Leeuwenhoek observed the myelinated nerve fiber although his interpretation was incorrect; and having discovered no cavities in the nerve itself, he found in the individual fibers the hollowness that the then current theory of nerve function demanded. The thin section of the nerves which he cut was probably the first ever” (Clarke and  O’Malley, The human brain and spinal cord. 2nd. Ed. [1996] 30-35, citing the Latin edition). The following year this edition was translated into Latin in 1719 and issued by the same publisher as Epistolae physiologicae super compluribus naturae arcanis; ubi variorum animalium atque plantarum fabrica, conformatio, proprietates atque operationes, novis & hactenus inobservatis experimentis illustrantur & oculis exhibentur; item peculiaries & hactenus incognitae rerum quarumdam qualitates explicatur: ut sequens pagina docet: hactenus numquam editae (Delft: Adriaan Beman, 1719.) Digital facsimile of the 1718 Dutch edition from the Biodiversity Heritage Library at this link. Digital facsimile of the 1719 Latin edition from the Hathi Trust at this link.