It was not possible to determine the adequacy of the content of our common foods in any of the inorganic elements until exact studies had been made to determine the efficiency of the animal body in absorbing and in conserving its supply. The variations in the inorganic content of the blood in health and disease are so small as to escape observation by any but the most modern and refined methods. Yet these variations are of great significance to the welfare of the individual. Unwarranted assumptions were made by the earlier students of nutrition, concerning the ability of the intestines to absorb mineral salts in a selective way so as to lead to the utilization with high efficiency those elements present in the food in small amounts. The capacity of the kidney to hold back those elements which are present in the food in minimal amounts and therefore reach the blood in amounts below the optimum was over rated. It is now known that the efficiency of the kidneys in preventing the passage of inorganic salts into the urine along with the waste products of metabolism, is not so great as to protect the body from losses which may be injurious to it when the food contains as little of such salts as those of calcium, phosphorus, sodium and chlorin as are contained in some of our most important cereal grains, tubers and meats. There are well defined limits to the degree to which the intake of these salts can be restricted without causing damage.