With the overturn of the old physiology underpinning Galenic medicine, new physiological foundations for medicine were searched for. Systems based on new physical principles proposed by Galileo and other physicists, and those on chemistry following its transformation from alchemy, were advanced: on physical principles by the iatrophysicists and on chemical principles by the iatrochemists. Both groups proposed agents to replace the ancient concept of animal spirits, but they essentially represented only a change of name. Alongside the nervous system by which sensations were perceived and motor nerves innervating muscles expressed the will, an involuntary nervous system was recognized – one by which the various bodily organs and its movements were carried out independently of the will (autonomously). Since Galen, the intercostal nerve chains were known, but were thought to be an offshoot of the vagus nerve originating from the brain, and it was so figured by Vesalius. These chains were then recognized as not connected directly to the brain, having its origin in neural connectives from the spinal cord. How the ganglia associated with this system, the intercostal chains and the ganglia found elsewhere with the involuntary nerves in the abdomen, their relation to the voluntary nervous system, and mode of action, became a matter of inquiry.

BOERHAAVE'S SYSTEM OF NERVE FIBERS

One of the most eminent clinicians of his day who incorporated the developments in physics and chemistry into a new system of physiology and medicine was Hermann Boerhaave (1668–1738), whose influential six-volume compendium, Institutiones medicae, was aimed at eliminating metaphysics from medicine and medical science.