silicon.
These simple substances are constantly passing out of the body through
the lungs, skin, and other excreting organs.
It is found that certain of these simple elements are used for one
part of the body, and others for other parts, and this in certain
regular proportions. Thus, carbon is the chief element of fat, and
also supplies the fuel that combines with oxygen in the capillaries
to produce animal heat. The nitrogen which we gain from our food and
the air is the chief element of muscle; phosphorus is the chief element
of brain and nerves; and calcium or lime is the hard portion of the
bones. Iron is an important element of blood, and silicon supplies the
hardest parts of the teeth, nails, and hair.
Water, which is composed of the two gases, oxygen and hydrogen, is the
largest portion of the body, forming its fluids; there is four times
as much of carbon as there is of nitrogen in the body; while there is
only two per cent as much phosphorus as carbon. A man weighing one
hundred and fifty-four pounds, who leads an active life, takes into
his stomach daily from two to three pounds of solid food, and from
five to six pounds of liquid.
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