Sylvius, Franciscus Dele Boë

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(b. Hanau, Germany, 15 March 1614; d. leiden, Netherlands, 15 November 1672)


Sylvius was of southern Flemish extraction. His grandfather, a merchant and descendant of a noble family, emigrated from Kamerijk (Cambria, now in France) to Frankfurt-am-Main. François was the second son of Isaäc dele Boë and Anna de la Vignette, who was from the same area of southern Flanders. For his primary education he was sent to Sedan, where a Calvinist academy had been established and where he received his first medical instruction. He then went to Leiden, where he studied medicine (1633–1635) under Adolph Vorstius and Otto Heurnius. After visiting the universities of Wittenburg and Jena, he received his degree at Basel on 16 March 1637, defending a thesis on “animal movement and its disorders”: De animali motu ejusque laesionibus. He already signed his name as Sylvius or, in order to avoid confusion with Jacques Sylvius (1478–1555), as dele Boë sylvius.

For a year and a half Sylvius practiced medicine in Hanau, but this seems not to have satisfied him. In any case, after a short study trip through France he returned to Leiden, where he hoped to obtain a post with the university. On 17 March 1638, he matriculated again and at his request received permission to give private lectures on anatomy, which met with great approval. He lectured on the Anatomicae institutiones of Caspar Bartholin but soon undertook to give anatomical demonstrations in the gallery of the botanic garden that were extended to physiological experiments. He was, in fact, one of the first to defend Harvey’s new theory of the circulation of the blood and demonstrate it on dogs. His vigor was so great that Johannes Walaeus (1604–1649), a sharp critic, became a fervent supporter of Harvey, in return making experiments on the new theory. At these demonstrations Sylvius seems to have met Descartes, who as early as 1637 had accepted Harvey’s theory of the circulation, although rejecting his concept of the action of the heart.

Because there seemed to be no prospect of an academic career at Leiden, Sylvius decided in the autumn of 1641 to move to Amsterdam, where he soon established a lucrative practice and earned the general esteem of his colleagues. He was appointed physician of the poor-relief board of the Walloon Church, and in 1657 he became a supervisor of the Amsterdam College of Physicians. His medical colleagues included Nicolaas Tulp, Paulus Barbette, and Hendrik van Roonhuyse; and his interest in chemistry brought him the friendship of Otto Sperling and J. R. Glauber. Despite the demands of his practice and professional commitments, he did not neglect scientific research work, performing postmortem examinations and devoting his spare time to chemical experiments.

In 1658, after extended negotiations, Sylvius was persuaded to accept appointment as professor of medicine at Leiden at the high salary of 1,800 guilders–almost twice the usual amount. On 17 September 1658 he delivered his inaugural oration, on the knowledge of man, De hominis cognitione. Devoting himself to his new task with great zeal, he proved to be an outstanding faculty member and his eloquence and gift for teaching attracted students from all parts of Europe. In bedside instruction, which he carried out in the old Caecilia Hospital, he showed himself to be an experienced clinician and a devoted teacher, who attracted many students from foreign countries. Although as a rule bedside teaching was limited to two days a week, Sylvius received permission to take his students daily to the hospital, where he performed the autopsies himself. His own ideas on several medical subjects were defended by his students in public disputations, and in 1669–1670 he was vicechancellor of the university. The first volume of his main work, Praxeos medicae ida nova, was published the following year, but he did not live to see the second volume in print.

In 1647 Sylvius married Anna de Ligne, the daughter of a lawyer, who was thirteen years younger than he. One or two children born of this marriage died at a very early age, and in 1657 his wife died. In December 1666 he married a twenty-two-year-old woman, who died three years later; their only daughter died in 1670.

Sylvius’ accomplishments were in anatomy and medical chemistry. Although there is some confusion with Jacobus Sylvius of Paris, a skilled anatomist who also worked on the brain, the Leiden Sylvius was responsible for the description of the fissura Sylvii and of the arteria cerebri media Sylvü, as well as of the fifth ventricle (pseudo ventricle, ventricle of the septum). The aquaeductus Sylvü was known to Galen and had been well described by Jacobus Sylvius. Moreover, Sylvius was the first to describe the tubercles in phthisis. In the history of medicine, however, Sylvius was the most brilliant representative of the iatrochemical school, founded by Paracelsus and continued by J. B. van Helmont, which reached its zenith when Sylvius defended the chemiatric conception from the Leiden chair. He was convinced that all physiological and pathological processes could be conceived perfectly in analogy to the processes and experiments observed in the chemical laboratory and could be explained by fermentation, effervescence, and putrefaction. Acid and alkali were considered as fundamental principles in the animal body.

In his therapeutics Sylvius preferred the new chemical medicines to the Galenic ones, using mercury, antimony, and zinc sulfate, among others. His rather speculative and extravagant theories included the belief that the pancreatic juice was acid and effervesced with the alkaline gall in the duodenum, and that ferments went to the heart, where he thought the blood effervesced. Considering the spleen to be the organ in which the blood is purified, he stressed its function to such an extent that he was called patronus lienis. In his last years Sylvius encountered public opposition from Anton Deusing, professor at Groningen, who–to Sylvius’ great displeasure–was appointed at Leiden University but died before he could assume his duties.

Although Sylvius, with his exaggeration, may have caused much harm in the medical practice of his students, he can nevertheless be considered a promoter of scientific medical research. His enthusiasm inspired several gifted students to valuable anatomical and physiological work: Jan Swammerdam, Nicolaus Steno, and Regnier de Graaf. Sylvius’ ideas on the pancreas induced De Graaf to attempt the experiments in which he obtained the pancreatic juice from a dog by means of a fistula.


I. Original Works. A more or less complete list of Sylvius’ writings is in Baumann’s biography (see below). They include De hominis cognitione, his inaugural oration (Leiden, 1658; Jena, 1674), reprinted with intro. and Dutch trans. in Opuscula selecta neerlandicorum de arte medica, VI (Amsterdam, 1927), 2–45; Disputationum medicorum decas (Leiden, 1670, 1674, 1676); and Praxeos medicae ida nova, 4 vols. (Leiden, 1671–1674). A collection of his works is Opera medica (Amsterdam, 1679).

II. Secondary Literature. See L. Schacht, Oratio funebris in obitum. Nobilissimi, Clarissimi, Expertissimi, D. Francisci de le Boe, Sylvü (Leiden, 1673); Frank Baker. “The Two Sylviuses. An Historical Study,” in Johns Hopkins Hospital Bulletin, 20 (1909), 329–339; E.D. Baumann, François dele Boë Sylvius, (Leiden, 1949), with portrait; Lester S.King, The Road to Medical Enlightenment 1650–1695 (London–New York, 1970), 93–112; and E. Ashworth Underwood, “Franciscus Sylvius and his Iatrochemical School,” in Endeavour, 31 (1972), 73–76.

G. A. Lindeboom