by François-Vincent Raspail in 1825, but Raspail's writings were unpopular, partly due to his republican sentiments. There is no evidence to suggest that Schwann and Raspail were aware of each other's work. Specialized cells Schwann was particularly interested in nervous and muscular tissues. As part of his efforts to classify bodily tissues in terms of their cellular nature, he discovered the cells that envelope the nerve fibers, which are now called Schwann cells in his honor. How the fatty myelin sheaths of peripheral nerves were formed was a matter of debate that could not be answered until the electron microscope was invented. All axons in the peripheral nervous system are now known to be wrapped in Schwann cells. Their mechanisms continue to be studied. Schwann also discovered that muscle tissue in the upper esophagus was striated. He speculated that the muscular nature of the esophagus enabled it to act as a pipe, moving food between the mouth and the stomach. In examining teeth, Schwann was the first to notice "cylindrical cells" connected to both the inner surface of the enamel and the pulp. He also identified fibrils in the dentinal tubes, which later became known as "Tomes's fibers". He speculated on the possible structural and functional significance of the tubes and fibrils. Metabolism In his Microscopical researches, Schwann introduced the term "metabolism", which he first used in the German adjectival form "metabolische" to describe the chemical action of cells. French texts in the 1860s began to use le métabolisme. Metabolism was introduced into English by Michael Foster in his Textbook of Physiology in 1878. References Further reading External links Schwann, Theodor and Schleyden, M. J. 1847. Microscopical researches into the accordance in the structure and growth of animals and plants. London: Printed for the Sydenham Society 1810 births 1882 deaths People from Neuss 19th-century German biologists German Roman Catholics People from the Rhine Province Recipients of the Copley Medal University of Bonn alumni University of Würzburg alumni Humboldt University of Berlin alumni Academic staff of the Catholic University of Leuven (1834–1968) Academic staff of the University of Liège Members of the Royal Swedish Academy of Sciences Foreign Members of the Royal Society Recipients of the Pour le Mérite (civil class) German physiologists