So much has been said in these pages of the importance of a suitable content of the mineral elements which the diet must furnish, that a few words of explanation as to the functions which they exercise in physiological processes may be of value to many readers, who are not physiologists or chemists.

Since the bones consist in great part of calcium, phosphate and magnesium the necessity for an adequate supply of these elements is easy to appreciate. Calcium salts are essential for the coagulation of the blood as it flows from a wound. When this element is removed from a sample of blood it cannot undergo clotting. Certain salts of calcium, especially the chlorid, greatly accelerate the rate of digestion of fats, through the agency of the fat digesting enzymes, or lipases.

For purposes of normal digestion in the stomach the presence of free hydrochloric acid in considerable amounts is indispensable since the pepsin cannot act upon the proteins of the food unless free acid be present. The acid of the stomach is derived from the sodium chlorid or common salt of our food. A liberal supply is necessary, and notwithstanding that the foods all contain a certain amount of it we are impelled by our appetites to make liberal additions of it in cookery, and as we eat, we "salt to taste."

The element sodium, which is a constituent of common salt, is also present in the blood in considerable amounts in the form of the bicarbonate, carbonate and phosphate. These act as "buffer" substances, i. e., they take up and neutralize the acids formed during metabolism, and aid in maintaining the body fluids in a state of neutrality which is a fundamental condition of life.

One of the prominent features of the functioning of living protoplasm is the presence of fluids within it which contain nicely adjusted amounts of certain mineral salts, which maintain what is known as osmotic pressure within the cells and between them and the body fluids.

Potassium is a constituent of all tissues of the body, but the relative amounts in different structures varies considerably. Only when there is a certain relation between the potassium, sodium and calcium concentration in the blood will the heart beat normally. Other functions of the mineral elements could be mentioned, in the performance of which each plays a specific role, and in the performance of which one element cannot be replaced by another without causing disturbances of metabolism or even death.