He made Marburg his home for the next ten years, studying and teaching anatomy and physiology, first as prosector to FL Fick (1841), then as privat-docent (1842), and finally as extraordinary professor (1846).

With his friends Hermann Ludwig Ferdinand von Helmholtz, Ernst Wilhelm von Brücke, and Emil du Bois-Reymond, whom he met for the first time in Berlin in 1847, he rejected the assumption that the phenomena of living animals depend on special biological laws and vital forces different from those that operate in the domain of inorganic nature; and he sought to explain them by reference to the same laws as are applicable in the case of physical and chemical phenomena.

[2] This point of view was expressed in Ludwig's celebrated Text-book of Human Physiology (1852–1856), but it is as evident in his earliest paper (1842) on the process of urinary secretion as in all his subsequent work.

Thus, his pupils gained a practical acquaintance with his methods and ways of thought, and, coming from all parts of Europe, they returned to their own countries to spread and extend his doctrines.

Possessed himself of extraordinary manipulative skill, he abhorred rough and clumsy work, and he insisted that experiments on animals should be planned and prepared with the utmost care, not only to avoid the infliction of pain (which was also guarded against by the use of an anesthetic), but to ensure that the deductions drawn from them should have their full scientific value.