Science in ferment: The doctrine of fermentation in seventeenth-century British science and medicine

The process of fermentation was quite literally the general factotum or do-all of early-modern science. It was used to explain an extraordinary number of phenomena, both organic and inorganic. Just as remarkable as the number of phenomena explained in terms of fermentation was the number of physicians and natural philosophers putting forth those explanations.; The doctrine of fermentation first arose as a new theory of gastric digestion. The subsequent use of this doctrine to explain virtually all physiological transmutations was a logical extension of the Scholastic tendency to see all such transmutations as digestions.; For centuries the process of digestion had been regarded as the archetype of natural change in general, and of physiological change in particular. According to the Scholastics, all digestions are caused by (what Galen called) the "alterative faculty" of the soul and its primary instrument, "innate heat." Though it was never entirely clear what the terms "innate heat" and "alterative faculty" were supposed to represent, this explanation of digestion went unchallenged for more than a millennium.; But in 1626 (more than twenty years before the publication of van Helmont's Ortus Medicinae), the physician Pietro Castelli pointed to a number of passages in the Hippocratic corpus that suggested another cause of digestion: acid ferments. By convincing the medical community that the concept of fermentation had greater explanatory power than the concept of innate heat, Castelli was able to initiate a quiet but significant revolution in medical thinking. The eventual rejection of the doctrine of fermentation was due primarily to its logical incompatibility with William Harvey's theory of the circulation of the blood.; Despite the excesses of some its most zealous adherents, the widespread acceptance of the doctrine of fermentation was a significant step in the history of science. Not only was the adoption of this doctrine closely associated with the rise of iatrochemistry and the mechanical philosophy, even more fundamentally, it represented the end of a centuries-long complacency with the status quo in physiology, and thus the beginning of a new era in biology and medicine.