An important new school of medical theory was the iatrophysical or iatromathematical (_iatros_ from the Greek--physician). This medical theory--as is the case with many scientific theories-was borrowed from another branch of science. The seventeenth century, the age of Isaac Newton, Galileo Galilei, Gottfried Wilhelm von Leibnitz, Rene Descartes, and other giants of physical science, was a period of remarkable progress in the field of physics. It is not surprising then that theorists in the field of medicine, noting the truths discovered by conceiving of nature as a great machine functioning according to laws that could be expressed in mathematical terms, should have attempted to explain the human body as a machine. William Harvey (1578-1657), whose name looms great in the history of seventeenth-century medicine, explained the circulation of the blood in mechanical terminology. To Harvey, working under the influence of the great physicists, the heart was a mechanical force pump and the blood was analogous to other fluids in motion. How many physicians, practicing in the same intellectual environment as this Englishman, must have carried the mechanical analogy to the extent of thinking of the teeth as scissors, the lungs as bellows, the stomach as a flask, and the viscera as a sieve? The iatrochemical school existed alongside the iatrophysical. Whereas the iatrophysical thought primarily in terms of matter, forces, and motions, the iatrochemical thought chemical relationships were fundamental. One of the founders of this school, the Dutch scientist Sylvius (1614-72), explained diseases chemically (an approach not completely unlike the humoral of Galen) and treated them on the basis of a supposed chemical reaction between drug and disease. Another leading figure in the iatrochemical school, Thomas Willis (1621-75), was an Englishman. These two advocated the use of drugs at a time when their respective nations were developing great colonial empires rich with the raw materials of pharmacology. However, it would be an error to think of the medicine of the period, either European or Virginian, only in terms of rational or scientific theories. Treatment was too often based on magic, folklore, and superstition. There were physicians relying upon alchemy and astrology; the Royal Touch was held efficacious; and in the _materia medica_ of the period were such substances as foxes' lungs, oils of wolves, and Irish whiskey. Nor should it be forgotten that many of the sick never saw a medical man but relied upon self-treatment.