‘The Organical Motions of Body Fluids’. Mechanical and Iatrochemical Theories in 17-Century Physiology Draft

Introduction According to the standard view of early modern science and medicine, two different approaches to human physiology dominated 17-century physiology. One was the iatromechanical, originating from Descartes, and the other was the iatrochemical, which started with Paracelsus and was subsequently articulated by Jean Baptiste van Helmont. Historians of science and medicine have drawn a firm line between iatromechanical and iatrochemical theories, emphasizing the differences of ideas and methods. The mechanists described human body and its parts in terms of matter and motion, namely by means of the shape, size and motion of particles of matter. The champion of iatromechanism was Descartes, who derived physiological processes from known mechanisms. As he put it in Traité de l’Homme “ I derive all these functions from the disposition of its organs alone, just as movements of a clock or another automat follow the disposition of counterweights and wheels”. For Descartes, living organisms do not differ in nature from nonliving things, and are the same as machines, their operations are performed by particles of inert matter following the laws of movement. Most iatromechanists followed a reductionist strategy, trying to deduce theories from the geometrico-mechanical properties of particles. By contrast, iatrochemists described human body as a chemical laboratory, the main physiological operations were deemed as chemical reactions, which they conceived as qualitative change. The iatrochemists rejected deductive logic and mathematics as useless to medicine and emphasised the importance of the empirical investigations. The ultimate ingredients of bodies (the three or five chemical principles) were conceived in qualitative terms. The chemical philosophers maintained