Spilt drop preparation showing renal tubular resorption : rat.

Shows lissamin-green passing through the kidney of a normal anaesthetized rat to determine the direction of flow in a long tubular loop. The loop is punctured with a double barrelled micropipette and filled with castor oil, stained with sudan-black. The oil column is then split by intratubular injection of unstained saline through the other barrel of the pipette. Reabsorption of fluid can be seen as distance between the oil columns decreases.