1638-86. In 1660, after spending three years studying medicine in Copenhagen, Stensen went to Amsterdam, where he made his first anatomical discovery: the duct between the parotid gland and the oral cavity (ductus parotideus stenonis).
In succeeding years in Leiden he explained the principal features of the physiology of the glands, at the same time as his contributions to embryology and comparative anatomy made him a researcher of European standing. Most discussed was his demonstration that the heart is neither more nor less than a muscle.
After failing to be appointed professor in Copenhagen in 1664, he spent a year in Paris, where in a famous lecture on the anatomy of the brain in 1665 he demonstrated the incorrect anatomical basis of cartesianism.
In his study of muscular physiology he was the first to argue that a mathematical description is also necessary in biology. After being employed at the Medici court in Florence, he converted to Catholicism in 1667.
He continued his scientific work with outstanding results, summing them up in his dissertation Prodomus (1669, English translation 1671), in which he laid the foundations of three new sciences. Palaeontology was given a solid foundation with the demonstration that fossils were petrified remains of living creatures.
As fossilised shark's teeth were found in mountains, these must once have been covered by the sea, so that the earth's crust must have undergone profound changes over the ages.
By means of field work Stensen succeeded in demonstrating and interpreting the geological stratification of Tuscany, whereby the principles of historical geology were established.
Finally, crystallography was given a scientific foundation through Stensen's demonstration that crystals grow when materials are deposited on their outer surfaces, the mutual angles of which remain constant during this process.
In 1672 Stensen returned to Copenhagen to a newly-established post as Royal Anatomist; he attracted many students from the university, which on several occasions invited him to carry out public dissections, but bypassed him in 1674 and appointed the 19-year-old Caspar Bartholin to a vacant Chair of Anatomy. This was partly responsible for Stensen's decision to return to Florence, where he was ordained priest in 1675 in order to devote the rest of his life to the service of the Church.
In 1677 he was consecrated bishop in Rome, after which he worked for the rest of his life among the widely dispersed Catholics of northern Germany and as a consequence of his vow of poverty came to live in extreme need.
After an unheeded visit to Copenhagen in 1685 he died the following year in Schwerin, from where his body was transported to Florence to be buried in the Medici church of San Lorenzo. He was beatified by Pope John Paul II in 1986.
Olaf Pedersen, Gyldendal Leksikon