A water solution that has the same salt concentration as the cells is said to be isotonic. Movement of water out of the cell is precisely stable and balanced by the movement of water into the cell when cells are in isotonic solution. For instance, a 0.9% solution of NaCl (saline) is considered isotonic to animal cells. It is normal to use an isotonic solution like Ringer's buffered saline in order to prevent consequent damage and osmotic effects to cells when exposing animal tissues to solutions.
