The question of the balance between acid and base-forming mineral elements in foodstuffs has figured more or less prominently in discussions of rations for both man and animals during the last decade. Based principally on the work of Forbes, Sherman and Gettler , and Castle, there has developed a considerable tendency to emphasize the necessity for a balance between potential acid and base in the mineral constituents of rations. In this preliminary discussion human dietary standards will figure, as well as rations for animals, but in reporting our conclusions we shall avoid the too common error of applying data obtained with one species to other species.