Osmosis, as described in 1825 by H.J. Dutrochet, played a role in the role in the beginning of physical chemistry and of the evaluation of renal functions. In 1871, the osmotic pressure, not so well understood by scientists, was again suggested by de Vries who described the "plasmolysis", a phenomenon corresponding to cell retraction when incubated in high molecular concentration solutions. Although the results were not well interpretated, this phenomenon was related to the osmotic pressure. Van't Hoff studied the mechanisms phenomena and compared it to the gas volume/pressure relationship. Dreser measured in urine the cryoscopic delta that had just discovered by Raoult in animal and man, after a water load (-0.20 degree C) or a water restriction (-2.50 degrees C) and calculated approximately the amount of energy required to eliminate water at various different concentrations of solutes. Koranyi used the same methods in disease states. The loss of difference between the maximal and minimal delta indicates a functional renal insufficiency. This was the term first proposed by Koranyi outlining the role of the kidney in the regulation of the milieu interieur and more specifically in the regulation of water and solute concentration. Hyposthenuria, best named isosthenuria, in the range of osmotic pressure usually indicates terminal renal failure. Koranyi named this test funktionelle Nierendiagnostik, a start for the physiological investigations of renal functions.