e germs.(33)
Partly through the small hairs in the nose, but mainly through the moist
membrane that lines the passages, the nostrils serve as filters for
removing the minute solid particles (Fig. 45). While it is important that
nose breathing be observed at all times, it is especially important when
one is surrounded by a dusty or smoky atmosphere. Otherwise the small
particles that are breathed in through the mouth may find a lodging place
in the lungs.

[Fig. 45]

Fig. 45--*Human air filter.* Diagram of a section through the nostrils;
shows projecting bones covered with moist membrane against which the air
is made to strike by the narrow passages. 1. Air passages. 2. Cavities in
the bones. 3. Front lower portion of the cranial cavity.

In addition to removing dust particles and germs, other purposes are
served by breathing through the nostrils. The warmth and moisture which
the air receives in this way, prepare it for entering the lungs. Mouth
breathing, on the other hand, looks bad and during sleep causes snoring.
The habit of nose breathing should be established early in life.(34)

*Cultivate Full Breathing.*--Many people, while apparently taking in
sufficient air to supply their need for oxygen, do not breathe deeply
enough to "freely ventilate the lungs." "Shallow breathing," as this is
called, is objectionable because it fails to keep up a healthy condition
of the entire lung surface. Portions of the lungs to which air does not
easily penetrate fail to get the fresh air and exercise which they need.
As a consequence, they become weak and, by losing their "power of
resistance," become points of attack in diseases of the lungs.(35) The
breathing of each individual should receive attention, and where from some
cause it is not sufficiently full and deep, the means should be found for
remedying the defect.

*Causes of Shallow Breathing.*--Anything that impedes the free movement of
air into the lungs tends to cause shallow breathing A drooping of the back
or shoulders and a curved condition of the spinal column, such as is
caused by an improper position in sitting, interfere with the free
movements of the ribs and are recognized causes. Clothing also may impede
the respiratory movements and lead to shallow breathing. If too tight
around the chest, clothing interferes with the elevation of the ribs; and
if too tight around the waist, it prevents the depression of the