air thus passing into and out of
the lungs is called tidal air. After an ordinary inspiration, the
lungs contain about 230 cubic inches of air. By taking a deep inspiration,
about 100 cubic inches more can be taken in. This extra amount is called
complemental air.

After an ordinary expiration, about 200 cubic inches are left in the
lungs, but by forced expiration about one-half of this may be driven out.
This is known as supplemental air. The lungs can never be entirely
emptied of air, about 75 to 100 cubic inches always remaining. This is
known as the residual air.

The air that the lungs of an adult man are capable of containing is thus
composed:

Complemental air 100 cubic inches.
Tidal " 30 " "
Supplemental " 100 " "
Residual " 100 " "
----
Total capacity of lungs 330 " "

If, then, a person proceeds, after taking the deepest possible breath, to
breath out as much as he can, he expels:

Complemental air 100 cubic inches.
Tidal " 30 " "
Supplemental " 100 " "
----
230

This total of 230 cubic inches forms what is called the vital
capacity of the chest (Fig. 90).

209. The Movements of Breathing. The act of breathing consists of a
series of rhythmical movements, succeeding one another in regular order.
In the first movement, inspiration, the chest rises, and there is an
inrush of fresh air; this is at once followed by expiration, the
falling of the chest walls, and the output of air. A pause now occurs, and
the same breathing movements are repeated.

The entrance and the exit of air into the respiratory passages are
accompanied with peculiar sounds which are readily heard on placing the
ear at the chest wall. These sounds are greatly modified in various
pulmonary diseases, and hence are of great value to the physician in
making a correct diagnosis.

In a healthy adult, the number of respirations should be from 16 to 18 per
minute, but they vary with age, that of a newly born child being 44 for
the same time. Exercise increases the number, while rest diminishes it. In
standing, the rate is more than when lying at rest. Mental emotion and
excitement quicken the rate. The number is smallest during sleep. Disease
has a notable effect upon the frequency of respirati