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Stensen N

Full Name: Niels Stensen

Nickname/Alias: Nicolaus Steno

Achievements: Anatomical studies of the glandular and lymphatic system; recognized the heart as a muscle; established the principles of historical geology; stated a fundamental concept in crystallography now known as the constancy of interfacial angles (“Steno's Law”)

Born: January 11, 1638 (Gregorian calendar); Copenhagen, Denmark

Died: December 5, 1686 (Gregorian calendar); Schwerin, Germany (Aged 48)

Field & Discipline: Science; Medicine; Anatomy; Geology; Paleontology; Crystallography

Language: Danish; Latin

Father: Sten Pedersen

Mother: Unknown

Siblings: Unknown

Spouse:Unknown

Children: Unknown

Education: University of Copenhagen; University of Leyden (MD, 1664)

Major Work:

“Observationes anatomicae” (“Anatomical Observations” 1662)

“De solido intra solidum naturaliter contento dissertationis prodromus” (“The Prodromus to a Dissertation Concerning Solids Naturally Contained Within Solids” 1669)

Life & Times:

As the son of a successful goldsmith (his father supplied the courts of two Danish kings) Stensen developed an early interest in the applied sciences.

However, he entered the University of Copenhagen in 1656 to study medicine, where he was a student of the respected anatomist [student of] Thomas Bartholin* (with whose son, [collaborated with] Erasmus Bartholin*,  Stensen later collaborated), known for his pioneering work on the lymphatic system.

Continuing his medical training, Stensen enrolled in the University of Leyden in 1660 and studied [influenced by] Paracelsus*, [influenced by] Santorio*, and [influenced by] Helmont*, among other renowned medical writers.

While at Leyden he also befriended a fellow student, [a pal of] Swammerdam*, who would become famous investigating the anatomy and life cycles of the insects using microscopic techniques. Leaving Leyden for personal reasons after three years, Stensen received his MD degree in absentia, in 1664.

Stensen's initial anatomical research, concerning the salivary glands, formed the basis of his dissertation at Leyden; the excretory duct of the parotid gland is still known as Stensen's duct (or Steno's duct).

Following the lead of Bartholin, his former mentor, Stensen broadened the scope of his investigations to include the entire glandular and lymphatic system, summarizing his findings in “Observationes anatomicae” (1662) and subsequent publications.

A meticulous anatomical observer, he also challenged the traditional assumption that the heart functions primarily to reheat the blood, arguing that “there exists nothing in the heart that is not found also in a muscle” (Stensen, quoted in the Dictionary of Scientific Biography).

This observation would lead him to pursue a more general investigation into the nature and cause of muscular contraction. Stensen also studied the anatomy of the brain, adopting the approach of Sylvius, one of his professors at Leyden. Already known primarily as Steno (his literary name), he had by now developed a formidable reputation as an anatomist.

In 1665, for instance, one observer reported on Stensen's public dissections before [demonstrated to] Thenard's*  scientific circle in Paris as follows: “When I called us apprentices next to M. Steno, I had reason, for I have never seen such dexterity. He made us see everything there is to see in the construction of the eye” (quoted in Porter & Teich, 1992, p. 19).

Unable to secure an academic post in his native Denmark, Stensen traveled to France and then Italy in search of employment. In 1666 he arrived in Florence, finding that his reputation had preceded him.

Florence was home to the Grand Duke of Tuscany, [employed by] Ferdinand II*, latest in a long line of rulers from the celebrated Medici family. The Grand Duke offered Stensen a medical position and arranged for his election to the [member of] Accademia del Cimento*, the academy of experimental science founded by Prince Leopold de' Medici, Ferdinand's brother.  Stensen's colleagues there included [colleague was] Viviani*, Galileo's former assistant, and [colleague was] Borelli*.

Stensen's arrangement with the Medici Court afforded him the opportunity to resume his research on the anatomy and function of muscles. In October 1666, when a great white shark was caught off the coast of Tuscany, the severed head, with its massive jaw muscles, was brought to Stensen for dissection.

At this juncture serendipity would dramatically alter the course of Stensen's scientific career. As a student at the University of Copenhagen, Stensen had seen a large collection of glossopetrae, or “tongue-stones,” many obtained by his professor, Bartholin, on a trip to Malta.

Known since antiquity, these curiosities were typically found lying on the surface of the ground or embedded in solid rock, often at locations far from the ocean. Named for their superficial resemblance to a pointed tongue with serrated edges, glossopetrae had been the subject of numerous fanciful hypotheses over the centuries, beginning with Pliny's suggestion that they must have fallen from heaven.

Stensen, however, immediately recognized an even stronger resemblance between tongue-stones and the somewhat smaller teeth of the great white shark brought to him for dissection. Allowing for the difference in size, he concluded that glossopetrae were in fact the fossil teeth of ancient sharks, gigantic even in comparison to the modern great white.

Stensen's first step was to address the prevailing idea that such “fossils” only resembled organic remains,  and had actually grown in place. To counter this argument he cited the frequent signs of wear and abrasion on tongue-stones as evidence that these were relics formed prior to being enclosed in rock. He also noted that the surrounding rock was usually layered, often horizontally, suggesting it had accumulated gradually as soft sediment; this process would have allowed the sediment to mold itself around the tongue-stones before it turned into rock.

From these initial observations, Stensen proceeded with a general inquiry into the various processes causing one solid to become enclosed within another solid: this was the theme of his famous “De solido intra solidum naturaliter contento dissertationis prodromus” (1669), known simply as the “Prodromus.”

In it he established rigorous criteria for differentiating organic remains like fossils from inorganic growths like crystals. Some of these criteria are discussed above, but another one bears mentioning: Stensen determined that the crystals of a specific mineral have constant interfacial angles, a principle now known as Steno's Law.

Even more important, the “Prodromus” included Stensen's formulation of the three basic tenets of historical geology, abstracted from his investigation into the origin of tongue-stones.

Stated in modern terms, he introduced the concepts of 1) the superposition of strata (the sedimentary layers in any sequence are progressively younger toward the top), 2) the original horizontality of strata (inclined strata must have been deformed after deposition), and 3) stratal continuity (partially eroded strata were initially continuous).

Using these deceptively simple concepts Stensen unraveled the geologic history of Tuscany and illustrated the sequence of events diagrammatically, thus establishing the importance of chronology in the study of earth history.

At the age of thirty-five, Stensen renounced science and, like his friend Swammerdam, turned to the spiritual life. Having converted to Catholicism in 1667, Stensen was ordained as a priest in 1675 and spent his remaining years serving the Pope.

Extra Connections: Stensen's anatomical research was related to that of [work related to] Malpighi*.

Stensen met [knew] Spinoza* in Leyden and was influenced by his rationalist philosophy.

He corresponded with [corresponded with] de Graaf*

Assessment: Nicolaus Steno, like Leonardo da Vinci, was cursed by his own versatility (Boorstin, 1983, p. 455)

Oneliner: Niles Stensen, major 17th -century Danish scientist

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