food--the value of these elements
becomes very evident, and their importance in the dietary inestimable.
Some of the mineral salts are more widely distributed in food than
others, and the danger arising from their deficiency in the diet is
not so great as is the case with others; hence attention is called to
those found by investigators to be most often lacking or deficient in
the average diet; _i.e._, calcium, phosphorus, and iron. A brief
summary of the special parts played by these elements will be outlined
here.

~Calcium.~--Physiology teaches that about eighty-five per cent. of the
mineral matter of the bone, or at least three-quarters of the ash of
the entire body, consists of calcium phosphates. It has long been
known that this mineral salt is necessary for the coagulation of the
blood, and science has demonstrated that "the alternate contractions
and relaxations which constitute the normal beating of the heart are
dependent, at least in part, upon the presence of a sufficient, but
not excessive concentration of calcium salts in the fluid which bathes
the heart muscles."[10]

~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 ce