It has long been known that the cerebrospinal fluid can not be the nervous system lymph, and Mestrezat, in his authoritative book of the year 1912, demonstrated it plainly. Davson has undertaken this subject and suggested the hypothesis of a sink action of cerebrospinal fluid, allowing a slow leakage of solutes from nervous tissue extracellular space. In order to test this hypothesis, Oldendorf and Dayson performed a series of animal experiments and they demonstrated that there was leakage of the solute into cerebrospinal fluid. Based on the idea of this sink action of cerebrospinal fluid, some possible physiological implications were considered such as the mechanism of origin of the ventricle-subarachnoid cerebrospinal fluid protein gradient; the mechanism of protection of the central nervous system against the harmful substances of the blood stream; and the homeostatic mechanism whereby the concentration of some ions of the fluid remains constant. Also, it is considered the possibility of a sink action of cerebrospinal fluid in the resolution of brain edema in water intoxication and other types of central nervous system edema.