Of the alkalies and alkaline earths, potassium, sodium, ammonium, lithium, calcium, magnesium, and barium are used in medicine. These, together with their many salts, alone constitute a large proportion of the inorganic materia medica. Whilst each of them is so important as to require separate consideration, many facts connected with their action and uses are common to the whole group, and much that is said under the head of Potassium, the first of the series, will not require to be repeated under the others.