The revolutionary "Zeitgeist" in the Europe of the 1840s left its mark no less in science than it did in the social and political life of the population. The essence of the scientific revolution was the change in paradigm from a vitalist-inductive to a mechanistic hypothetico-deductive approach, in which the experiment assumed the central role. The initiator of this new approach was a young physiologist in Marburg, Germany-Carl Friedrich Wilhelm Ludwig- and the first document his 1842 Habilitation thesis. Although this thesis was limited to a study on renal function, the impact of this epochal new approach, namely the analysis and explanation of living phenomena solely on the basis of physics and chemistry, went far beyond renal physiology: it revolutionised thinking in all the biological sciences. In this thesis, Carl Ludwig enunciated the principle of glomerular ultrafiltration driven by physical forces alone, i.e., the difference in the hydrostatic and oncotic pressures of the blood in the glomerular capillaries, a concept which remains valid today. Ludwig thus became the first scientist to describe correctly a principal component of renal function, the process of glomerular filtration.