THE NAME "lithium" from the Greek lithos, meaning stone, was conferred on an elusive constituent of rocks early in the last century. Arfwedson was able to show that it chemically resembled sodium and potassium in some reactions but not in others. It occupies the third box in the periodic table because the three protons in its nucleus give it three units of electric charge and an atomic number of three. Its atomic weight (6.94) makes it the third lightest element after hydrogen and helium.1 The hydrated radius and atomic charge density of the lithium ion would lead to the prediction that it would behave more like sodium than potassium in biological systems.
In 1949 Cade used lithium to treat mania.2 It has repeatedly been shown to be effective in the treatment and prevention of the manic phase in manic-depressive disease. There is little effect on