Nicolaus Steno

1631-1687

Danish Anatomist, Naturalist, and Physician

Nicolaus Steno was one of the great scientists of the seventeenth century. Best known today for his views on fossils and as the founder of stratigraphy, he was trained as a physician and did important work in anatomy, crystallography, geology, and paleontology.

Steno, whose real name was Niels Steensen (sometimes spelled Stensen), was born on January 1, 1631, in Copenhagen, Denmark. Raised a devout Lutheran, he entered the University of Copenhagen in 1656 to study medicine. He continued his studies at the University of Leiden (1660-1663), receiving his M.D. in absentiawhile in Paris (1664). After making important anatomical discoveries he traveled to Italy, where in 1666 he was appointed court physician to Ferdinand II, Grand Duke of Tuscany (1610-1670). His most significant geological and paleontological results were developed during his stay in Florence. He converted to Catholicism in 1667 and returned to Copenhagen in 1668 to accept the position of royal anatomist. After becoming a priest in 1675 he abandoned science completely and devoted his remaining years to the Catholic Church. He died in acute pain from gallstones at Schwerin, Germany, on November 25, 1686.

In 1660 Steno discovered the parotid gland (Steno/Stensen's duct)—the oral cavity's principal source of saliva. His further investigations led to a basic understanding of the lymphatic system as a whole. In Observationes anatomicae (1662) and De musculis et glandulis (1664) Steno presented his new discoveries, describing the structure and function of other glands including the lachrymal apparatus, which facilitates the movement and cleansing of the eye, the nasal duct, the earwax duct, ducts of the cheek glands, smaller ducts under the tongue, and the glandular ducts of the epiglottis and palate.

Beginning in 1662 Steno conducted research on muscles from which he developed a comprehensive view of their structure. He showed that muscle tissue contains arteries, veins, and nerves, and is composed of closely woven fibers. Steno described the function of the diaphragm during respiration, classified the tongue as a muscle, and advanced the then-novel idea that the heart is nothing more than a muscle with contractions controlled by muscle fiber. From 1665 to 1667 he worked on brain anatomy, embryology, and comparative anatomy. During this period he demonstrated that animals possess a gland resembling the pineal gland of humans. This undermined René Descartes' (1596-1650) claim that the pineal gland was the seat of the uniquely human soul.

The catalyst for Steno's paleontological, geological, and mineralogical discoveries was his dissection of a huge shark caught near Leghorn, Italy (1666). His examination of the shark's teeth revealed their similarity to glossopetrae (tonguestones, so called because of their resemblance to petrified serpent or bird tongues) found on Malta and elsewhere. These and other fossils were widely believed to be either direct productions of nature or God. Steno challenged these views in De Solido intra Solidum naturalites contento dissertionis Prodromus (1669), maintaining the organic origins of fossils.

Prodromus contains the outlines of modern geology. Steno argued that fossils are animal remains that had become embedded in sea-floor strata and then petrified by the concreting action of chemical forces, heat, and compression over time. He suggested that strata are deposited horizontally in layers from aqueous fluids with occasional crustal collapses accounting for diversities of topography. In explaining this stratification he established the principle of superposition—underlying sedimentary layers are older than those overlaying them—upon which modern geochronology is based. To accompany his explanations, Steno produced what are considered the earliest geological cross sections. In this same treatise, attempting to account for crystallization, he propounded Steno's law—angles formed by corresponding faces of quartz crystals remain constant for a given mineral.

STEPHEN D. NORTON