y:
oxygen, hydrogen, nitrogen, chlorine, fluorine, carbon, phosphorus,
sulphur, calcium, potassium, sodium, magnesium, and iron. Besides
these, a few of the other elements, as silicon, have been found; but they
exist in extremely minute quantities.

The following table gives the proportion in which these various elements
are present:

Oxygen 62.430 per cent
Carbon 21.150 " "
Hydrogen 9.865 " "
Nitrogen 3.100 " "
Calcium 1.900 " "
Phosphorus 0.946 " "
Potassium 0.230 " "
Sulphur 0.162 " "
Chlorine 0.081 " "
Sodium 0.081 " "
Magnesium 0.027 " "
Iron 0.014 " "
Fluorine 0.014 " "
-----
100.000

As will be seen from this table, oxygen, hydrogen, and nitrogen, which are
gases in their uncombined form, make up 3/4 of the weight of the whole
human body. Carbon, which exists in an impure state in charcoal, forms
more than 1/5 of the weight of the body. Thus carbon and the three gases
named, make up about 96 per cent of the total weight of the body.

7. Chemical Compounds in the Body. We must keep in mind that, with
slight exceptions, none of these 13 elements exist in their elementary
form in the animal economy. They are combined in various proportions, the
results differing widely from the elements of which they consist. Oxygen
and hydrogen unite to form water, and water forms more than 2/3 of the
weight of the whole body. In all the fluids of the body, water acts as a
solvent, and by this means alone the circulation of nutrient material is
possible. All the various processes of secretion and nutrition depend on
the presence of water for their activities.

8. Inorganic Salts. A large number of the elements of the body unite
one with another by chemical affinity and form inorganic salts. Thus
sodium and chlorine unite and form chloride of sodium, or common salt.
This is found in all the tissues and fluids, and is one of the most
important inorganic salts the body contains. It is absolutely necessary
for continued existence. By a combination of phosphorus with sodium,
potassium, calcium, and magnesium, the various phosphates are formed.

The phosphates of lime and soda are the most abundant of the salts of the
body. They form more than half the material of the bones, are found in the
teeth and in