AbstractMechanicism and organicism (vitalism) are two basic positions in the study of life processes. They can be reduced in a simplifying manner to a scheme Demokritos‐mechanism‐causality and Aristotle‐organism‐finality. The essentially mechanistic thought of the enlightenment lost all its influence in Germany through the speculative tendencies of natural philosophy. For the physiology between 1780 and 1840 physics and chemistry became only auxiliary sciences applicable to some special problems (Merkel, Rudolphi, Tiedemann, Johannes Müller). In the middle of the 19th century ‐ after remarkable attempts of the brothers Weber (1825, 1827) ‐ comes a complete change in the direction of physico‐mechanistic research. The first representative textbook of a quantitative‐measuring physiology is that of G. G. Valentin (1844). Decisive for the development of modern physiological science is the discovery of the laws of thermodynamics (Mayer, Joule, Helmholtz, Clausius, Boltzmann) demonstrating the same forces acting in organic and inorganic processes. The transformation of physiology into a physico‐mechanistic science is due in the first instance to du Bois‐Reymond, Ludwig, Brücke and Helmholtz who formulated the new program and controbuted by their results so that physiology would be recognized as an exact natural science. The intellectual situation in France (Dutrochet, Poiseuille, Claude Bernard) can be parallelised. The „biological philosophy”︁ of A. Comte, however, demands peculiar attention. The next generation (L. Hermann, R. Heidenhain, A. Fick, J. Bernstein) helps to consolidate modern physiology, which incorporates physical chemistry (1887) as its most recent branch. The mechanistic necessity leads namely A. Fick and H. Helmholtz to a new philosophical understanding of physical reality. The contribution of the 19th century to mechanize the experimental life sciences made from physiology an autonomous science no longer directed by pure utility and which escaped fr