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A Mutual Divide: Experiment vs. (Cartesian) Speculation in Mid-Seventeenth Century Dutch Medicine

This is a guest post by Evan Ragland.

In 1639, the Dutch anatomist and physician Franciscus Dele Boë Sylvius (1614-1672) thrust experimental physiology before the public eye when he demonstrated the Harveian circulation of the blood in the Leiden public gardens. These anatomical investigations unfolded within and partially constituted the growing controversy over the motion of the heart and blood. At some key moments, this controversy resembled the structure and rhetoric of the experimental-speculative distinction.

For the anatomists, Harvey’s description of a muscular heart contracting at systole to expel blood into the arteries was observationally and experimentally proven.  In contrast, many leading anatomists found Descartes’ anatomy to be fallacious and outmoded. Sylvius’ demonstrations convinced one critic, Johannes Walaeus (Jan de Wale, 1604-1649), who became an ardent supporter of the circulation. In 1645, Walaeus attacked the Cartesian explanation of the heart’s motion:

    Certain men with brilliant minds [ingenium praeclarum] judge that the blood is thrust out because it is immeasurably rarefied by the heat of the heart, and so demands a bigger place, and then dilates and lifts up the heart. […] [Yet] in truth the blood does not leap out from the heart on account of the rarefaction, as we have often seen in strong dogs with the tip of their hearts cut off. Because of the outflow of the blood, the heart is not half filled, but still erect: thus, it is not filled by rarefaction. In the subsequent constriction the portion of the blood in the heart was ejected more than four feet, so that we and our neighbors in the large crowd were befouled. From which it is evident that the blood is propelled by the part.

Strikingly, at least one of Descartes’ close friends and supporters, Cornelis van Hogelande (1590-1676), embraced the distinction between experimental and speculative approaches the anatomists propounded, but favored the speculative method.

“The Neoterics,” following after Harvey, added superfluous experimentation to already conclusive reasoning. They proceeded, “not only according to the manifest laws of mechanics […] but, instead, not having enough trust in the grace of reasoning [ratiocinatio], they turned themselves to girding and supplementing these laws with scrutinizing investigations or real and sensual disquisitions, and to dissecting living animals of every kind.”

For his own positive account, Van Hogelande relied on reasoning from mechanical principles. He could, though, throw a bone to the experimentalists:

    As a favor to those who are distrustful of ratiocination and believe experience alone, I will not be amiss in adding on the following easy experiment, in confirmation of the truth of the aforesaid [conclusion]. [Experiment dissecting an eel’s heart, and then adding blood when the motion has ceased, causing increasing motion.] [A]nd I even repeated this experiment in its particularities with similar success, while the printer hurried. Which I add lest anyone assume that I collected those preceding reasons a posteriori (that is, with the experiment having first been done).

This division lasted. In his later medical disputations from the late 1650s and early 1660s, Sylvius set out to resolve the dispute between Harvey and Descartes, “the two most brilliant Lights of this age.” Harvey taught “according to the custom of the Physicians, as well as the Sensible Philosophers, and according to the testimony of the external Senses.” Descartes, on the other hand, “trusting more in the laws of his own Mechanics, rather than in his external Senses, suspected and believed that the Ventricles of the Heart and the Arteries were Dilated and Contracted simultaneously.” Once again, the distinction between experimental anatomy and Cartesian speculation is crisp:

    For whatever even the most subtle and sagacious Genius [Ingenium] is able to think up that is most probable and plausible to the human Mind, every such thought, if it looks to the Medical Art, ought to be suspected as False by the Prudent, until Experience the Teacher of Truth has manifested that it is True, that is, that it has actually been observed in the things themselves as it has been imagined [fingitur].
    God forbid that among the legitimate Sons of Physicians anyone should be discovered who is so lazy, that they […] would rather delight in adhering to his own figments and Chimeras, and to those of others.

Shortly after, Sylvius freely admitted that Descartes was a “famous Mathematician and industrious Philosopher.” Drawing the lines of discipline and identity so that Descartes remained a successful mathematician and philosopher was the gentlest criticism, but one that barricaded him from a place among “the legitimate Sons of Physicians.”

There are, however, complications for this neat typology. Several Dutch anatomists at the time evinced some support for Cartesian philosophy, and later professors of medicine were staunchly Cartesian. And Sylvius repeatedly announced his support for something very like Cartesian mechanism as the preferred and future form of explanation and ontology, even in medicine. Yet a mutual division similar to the ESD remained at the heart of these early anatomical controversies.