[Chemistry of life: ferments and fermentation in 17th-century iatrochemistry]

The concepts of ferment and fermentation played an important, though heretofore neglected, role in 17th-century physiology. Though these notions can be found in ancient philosophy and medicine, as well as in medieval medicine, they became integral part of the chemical medicine that was advocated by Paracelsus and his school. Paracelsians made fermentation a central concept in their successful effort to give chemical foundation to medicine. Jean Baptiste van Helmont and Sylvius used the concepts of ferment and fermentation to explain a variety of physiological processes in human body. Corpuscular philosophers like Robert Boyle and Thomas Willis reinterpreted these notions in corpuscular terms and separated the concept of ferment from that of fermentation. In the second half of the seventeenth century, physiologist tried to explain fermentation by means of chemical reactions, as for instance acid -alkali, and ruled out the notion of ferment as superfluous to their investigations. At the end of hte seventeenth century fermentation attracted the interest of physicists like Johannes Bernoulli and Isaac Newton, who tried to explain fermentative processes in terms of matter and motion (Bernoulli) and short-range forces (Newton). George Ernst Stahl devoted a work to fermentation: the Zymotechnia. He explained fermentation as the outcome of the reactions of molecules formed of saline, oily and earthy corpuscles with particles of water. He saw fermentation as a mechanical process, i.e. as collision of different kinds of corpuscles.