(_a_) It is the greatest known solvent. Because of this property,
water is extremely important in the processes of digestion. (See
_Solution and Digestion_.)

(_b_) It is a great carrier. Water helps carry food materials to all
parts of the body; and it aids in carrying off the wastes of the body.

(_c_) It assists in regulating the temperature of the body. Because
water is present in blood, and blood flows from the warmer interior of the
body to the colder exterior, the water aids in distributing the heat of
the body. The evaporation of perspiration, which is largely composed of
water, also aids in regulating body temperature.

It is thus readily seen that water is needed to keep the machinery of the
body working smoothly. The uses of water may be summed up in the
statement: _Water aids in regulating body processes_.

FOREIGN MATERIALS IN WATER.--Since water is such a ready solvent, it
contains many foreign materials. In passing through the air and in flowing
through the ground, it dissolves many substances. Some of these substances
are harmless, while some contain disease bacteria and are dangerous. Well
water is frequently contaminated. It is often not safe to use for drinking
purposes unless boiled.

EXPERIMENT 7: PRESENCE OF GASES IN WATER.--Fill a beaker half full of
water, and note its temperature. Heat the water, and observe the changes
which take place. What appears on the sides and bottom of the beaker? What
does water contain which is driven off by heat?