Seventeenth Century

The classical assumptions of humoralism that had explained human functioning in health and disease for nearly two millennia in the Western world were severely challenged in the seventeenth century. During this century, the body came to be viewed as something like a machine governed by physical principles. This view was expressed by the philosopher René Descartes in a treatise published posthumously in 1662. Cartesian man had a dual nature: a physical body ruled by universal laws of matter and motion, and an immaterial soul or mind-a pure thinking entity - located in the pineal body of the brain. The body was conceived of as a vast hydraulic network of hollow pipes, moving blood and nervous fluid in the circulatory and nervous systems under the influence of the mind.

Descartes's mechanical theory spawned a mechanical school of human physiology located primarily in northern Italy,- where Galileo Galilei, the great physicist, had already established a science of mechanics. Following in Galileo's footsteps, a mathematician, Giovanni A. Borelli, analyzed the phenomenon of muscular contraction and a physician, Sanctorius of Padua, studied metabolic combustion and insensible perspiration.

In England, William Harvey's experimental discovery of the blood circulation, announced in 1628, contributed to the mechanical view of living organisms while discrediting Galen's fanciful hypothesis of a humor ebb and flow. The heart was now viewed as a pump, its chambers closing tightly with the help of valves. Blood was impelled into an intricate system of vessels according to the laws of hydrodynamics and traveled in a close circle through the arterial, venous, and capillary systems.

Not only did Harvey's findings support a mechanistic view of the human organism, but his approach to the theory - which included dissections, animal experiments, and mathematical reasoning - demonstrated the potential usefulness of scientific research in resolving physiological questions. On the basis of the ideas of Pierre Gassendi, a seventeenth-century French philosopher, regarding the corpuscular nature of matter, various British investigators working in concert studied the phenomenon of respiration. By the 1670s, Robert Boyle, Robert Hooke, Richard Lower, and John Mayow had concluded that certain air particles entering the lungs and mixing with arterial blood were essential for all vital functions. At the same time, chemical fermentation studies by Jean Baptiste van Helmont and François de la Boë explained the nature of digestion. Microscopic studies, carried out by Anton van Leeuwenhoeck in Holland using a single-lens instrument with a magnification of about 300 diameters, remained unequivocal.

Although corpuscular dynamics replaced traditional humors and their qualities in the explanation of human physiology, clinical medicine failed to benefit from the new medical theories. Practitioners treating the sick could not readily apply these views to the therapeutic tasks at hand, preferring instead to prescribe their traditional cures by adhering to obsolete ideas of humoral corruption and displacement. Thomas Sydenham, a prominent English phy sician, urged his colleagues to ignore the conflicting theoretical views, proposing instead the careful study of individual diseases at the bedside. Sydenham's goal was the establishment of complete clinical descriptions of particular diseases, their subsequent classification, and the development of specific remedies for each identified ailment.

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