ght of the oxygen. Since
oxygen comprises about one fifth of the atmosphere, the pressure
which it exerts is about one fifth of the total atmospheric
pressure, or, at the sea level, about three pounds to the square
inch (15 x 1/5 = 3). This is the oxygen pressure of the atmosphere.
The low oxygen pressure in the tissues is due to its scarcity, and
this scarcity is due to its entering into combination at the cells.

47 See footnote on oxygen pressure, page 109.

48 The impression prevails to some extent that carbon dioxide, on
account of its weight, settles out of the atmosphere, collecting in
old wells and at the floor in crowded rooms. Any such settling of
the carbon dioxide is prevented by the rapid motion of its
molecules. This motion not only prevents a separation of carbon
dioxide and air after they are mixed, but causes them to mix rapidly
when they are separated, if they still have surface contact. The
carbon dioxide found in old wells is formed there by decaying
vegetable or animal matter. In rooms it is no more abundant at the
floor than in other parts.

49 On account of the formation of carbon dioxide in places containing
decaying material, the descent into an old well or other opening
into the earth is often a hazardous undertaking. Before making such
a descent the air should always be tested by lowering a lighted
lantern or candle. Artificial respiration is the only means of
restoring one who has been overcome by this gas (page 97).

50 While awaiting oxidation at the cells, the carbohydrates and fats
are stored up by the body, the carbohydrates as glycogen and the
fats as some form of fat. In this sense they are sometimes looked
upon as serving to build up certain of the tissues.

51 The following table shows the main elements in the body and their
relation to the different nutrients:

[Nutrient Table]

52 The recently advanced theory that the molecules of the mineral
salts, by dissolving in water, separate into smaller divisions, part
of which are charged with positive electricity and part with
negative electricity, has suggested several possible uses for sodium
chloride and other mineral salts in the body. The sodium chloride in
the tissues is in such concentration as to be pra