The mineral ingredients of the body are essential to the maintenance of life, to give the body form and stability, and to maintain numerous special functions. Doubtless they take large part, by so-called catalytic action, in the more recondite chemistry of cells and fluids. They are obtained in abundance, even in excess, in the foods that are ordinarily eaten. In health, sodium chlorid is the only salt that need be added to foods.

Sodium chlorid is found in all the tissues and fluids of the body. It is most abundant in the latter. It performs various functions. It gives relish to the food that contains it and improves appetite. From it the hydrochloric acid formed by the glands of the stomach, and so essential to digestion, is produced. It promotes the diffusion of fluids through membranes. It keeps globulins in solution in blood and lymph. It stimulates protein metabolism and increases the excretion of urea. Partly by increasing metabolism and the production of waste, and partly of itself, it stimulates the kidneys to increased activity. It is of value as a mild laxative. When taken the first thing in the morning with water, it will often promote free catharsis in those who are constipated. It is an important element in many laxative mineral waters. An adult in health will eat and eliminate 200 grains of sodium chlorid daily. The kidneys are the organs through which it is chiefly excreted. It is used extensively as a food preservative. Beef, pork, and fish are commonly "salted" in order to preserve them.

Sodium carbonate and bicarbonate are found in the blood. They are present in the foods consumed, and are also formed in the alimentary tract by the decomposition of salts of the vegetable acids. Their presence in the blood is important because they help the plasma to carry carbonic acid from the tissues to the lungs for elimination.

Sodium and potassium sulphate occur in small quantities in the body. In part they are eaten as such, and in part are formed in the body by the oxidation of organic substances containing sulphur.

Sodium and potassium phosphates also are important mineral constituents of the body, and are distributed widely therein. The alkaline phosphates give to the blood and lymph their alkaline reaction, and the acid sodium phosphate gives the urine its usual acid reaction.

Potassium chlorid is widely distributed in the body, but it occurs in comparatively small proportion. It is most abundant in the muscle-cells and the red blood-cells. In general it may be said of potassium that it is most abundant in the cells of tissues, and of sodium that it is most abundant in the fluids.

Calcium phosphate and calcium carbonate are associated in the tissues. The former is much the more abundant, forming more than half of bone. It is essential to all cell growth, and is present in all tissues. Magnesium phosphate occurs with the lime-salts, but occurs in much smaller quantity.

Sulphur and phosphorus are introduced into the system with the albuminates. They occur in both animal and vegetable foods.

Iron is essential to the maintenance of health. It is an important ingredient of hemoglobin, and occurs in appreciable amounts in muscle-fibers, and in minute amounts in various other tissues. Only a small quantity of iron is needed to maintain its balance in the system. In anemic states it is deficient in the blood; sometimes, however, this deficiency is due to a destruction of hemoglobin or of red corpuscles which cannot be prevented by administering iron.

Iron is eliminated by the mucous membrane of the intestines but only in small amounts. Most of what appears in the feces when food which is rich in iron is eaten passes through the intestines not having been absorbed at all.

There has been much discussion as to whether inorganic salts of iron are absorbed and if so whether they can make hemoglobin and other compounds in tissues containing iron. It has been proven that it can be absorbed and stored in tissues, but that it cannot contribute to the production of iron compounds in cells. What is needed for their production must be derived from the organic iron of foods. However, as has been known for very many generations inorganic iron can stimulate blood formation when anemia exists, that is, it can stimulate the appropriation of organic iron by cells needing it.

The human body contains relatively the largest amount of iron at birth. As the food of infants in the first months contains very small quantities, this stored iron is drawn upon for the growth of blood during the period of rapid body development.

For the maintenance of iron equilibrium in an average man ten to twelve milligrams of food-iron are required daily. It is probably safest to fix the standard for a diet at fifteen milligrams which is close to what is obtained from an ordinary diet. Average American dietaries afford twelve to nineteen milligrams. The iron in meat is chiefly in the blood which it contains. The following table shows the percentage in some common foods:

An excess of salts will sometimes irritate the organs of digestion. An excess of lime and phosphates often gives rise to the formation of calculi in the urinary channels. Their absence is a cause or concomitant of rachitis. It is probable, however, that in this malady other salts also are deficient. The absence of the salts of vegetable acids is said to be an important element in the causation of scurvy.

Most mineral salts undergo no change of form in the system. They are found in the tissues in the form in which they are eaten, and are eliminated in the same condition. Some notable exceptions to this rule occur; these have already been referred to. Iron, for example, is greatly modified before it is combined with protein in the blood-corpuscles and muscle-cells.

Mineral salts are chiefly eliminated by the kidneys and intestines. They are also eliminated to a small extent by the skin. They are contained in various secretions as products having functional utility or as excretions.

Sodium chlorid when eliminated in large quantities causes renal casts to form and albuminuria. In much smaller amounts it is an irritant to kidneys already inflamed. Moreover, it has been found to often accumulate in the tissues of those who have disease of the heart or kidneys and then to lead to the production of dropsy. In these cases it must be almost excluded from the diet in order promptly to effect the absorption and elimination of the dropsical fluid.

As a rule, little attention is given to supplying salts to meet the needs of the body when more is required than is found in the meats and vegetables that are eaten. This need should be remembered, however, when but small quantities of food, or foods greatly diluted with water, are taken. Infants who do not digest cow's milk well are often given milk so much diluted with water that it is deficient in both fats and salts. Such children are especially likely to develop rachitis.