~Phosphorus.~--According to Sherman, phosphorus compounds are as widely distributed in the body, and as strictly essential to every living cell as are proteins. Science has also proved that they are important constituents in the skeleton, in milk, in glandular tissue, in sexual elements, and in the nervous system; that these compounds take part in the functions of cell multiplication, in the activation and control of enzyme actions, in the maintenance of neutrality in the body; that they exert an influence on the osmotic pressure and surface tension of the body, and upon the processes of absorption and secretion. Like calcium, phosphorus is absolutely essential to the growth and development of the body, and, as in the case of the mineral, its presence in the dietary must be accorded strict attention, in order to avoid the results accruing from its deficiency. Casein, or caseinogen of milk and egg yolk (ovovitellin), are the substances richest in this mineral salt. The fact that the phosphorus existing in grains (cereals) may be removed largely in the process of milling, makes it advisable to consider the use of the breads made from the whole grains. ~Iron.~--The presence of iron as an essential constituent of hemoglobin has already been discussed. That which is not in the hemoglobin is chiefly found in the chromatin substances of the cells. The body does not keep a reserve store of iron on hand as is the case with calcium and phosphorus in the bone tissues, but must depend upon the daily intake in food to supply its needs. The iron content of food materials is not large, but a careful regulation of the iron bearing foods (see Table on page 5) will make it easy to cover the demands of the body with a material which has been found to do its work most efficiently. Medicinal iron has received much attention in the determination of the essential needs of the body. "Whether medicinal iron actually serves as material for the construction of hemoglobin is not positively known, but we have what appears to be a good evidence that food iron is assimilated and used for growth and for regeneration of the hemoglobin to much better advantage than are inorganic or synthetic forms, and that when medicinal iron increases the production of hemoglobin, its effect is more beneficial in proportion as food iron is more abundant--a strong indication that the medicinal iron acts by stimulation rather than as material for the construction of hemoglobin." (Sherman)