All media used in tissue culture have a basis of a synthetic mixture of inorganic salts known as a physiological or balanced salt solution (BSS). All the physiological salt solutions have been derived from the salt solution originally described by Sydney Ringer (1885). The first balanced salt solution to be developed specifically for supporting the metabolism of mammalian cells was Tyrode's solution. Since then many modifications have been done to obtain better buffering salt solutions and to prevent calcium precipitation. The function of a salt solution is: ·To maintain the medium within physiological pH range. ·To maintain intracellular and extra cellular osmotic balance. ·Modified with a carbohydrate, such as glucose serves as an energy source for cell metabolism. Earle's balanced salt solution is designed to equilibrate with a 5% CO2 in air mixture. TL1002 is Earle's balanced salt solution with phenol red and sodium bicarbonate hence requires the cells to be grown in a 5% CO2 environment.