The air should be inhaled through the nose. It does not matter much how
it is exhaled. The nose is so constructed that it fits the air for the
lungs. The inspired air is often too dry, dusty and cold. The normal
nose remedies all these defects. The mucous membrane in the nasal
passages contains cilia, which catch the dust. The nasal passages are
very tortuous so that during its journey through them the air is warmed
and takes up moisture.
Habitual mouth breathing is one of the causes of the hardening and
toughening of the mucous membrane of the respiratory passages, for the
mouth does not arrest the irritating substances floating in the air, nor
does it sufficiently warm and moisten the inspired air. Irritation
produces inflammation and this in turn causes thickening of the
membranes. Then it is very easy to acquire some troublesome affliction
such as asthma. Very cold air is irritating, but the passage through the
nose warms it sufficiently.
The evil results of mouth breathing are well seen in children, in whom
it raises the roof of the mouth and brings the lateral teeth too close
together. Then the dentists have to correct the deformity and the
children are forced to suffer protracted inconvenience.
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