=Reasons for Breathing through the Nose= (Fig. 83).--(1) The many blood vessels in the mucous membrane lining the nasal passages so _heat the air_ that it does not irritate the bronchial tubes. (2) _The hairs in the nostrils strain the air_ and catch dust; the cilia of the nasal passages also do this. (3) A mouth-breather often _swallows food before chewing it sufficiently_, because he cannot hold his breath longer. (4) The nasal mucous membrane of an habitual mouth-breather _dries and shrinks_ and obstructs the circulation, bringing on _catarrh of the nose_. (5) Mouth breathing causes an _unpleasant expression of countenance_ (see Fig. 84). (6) The breath does not come through the nose as quickly as through the mouth; the _lungs are kept more expanded_, and one does not get “out of breath” so quickly. (7) _The voice of the mouth breather has a hard twang_, not a full, resonant tone as when the nostrils are open. (8) _Flavors and odors_ are better appreciated. Sometimes the sense of smell is almost lost by mouth breathers. If one cannot breathe through the nose, even for a short time, there is probably an adenoid, or tonsil-like, growth in nose or pharynx, and a physician should be consulted. “Adenoids” are glandular or grapelike in form. =Diseases of the Respiratory Organs.=--_A cold or catarrh is an inflammation of a mucous membrane._ If the inflammation is in the nasal passages, it is called a _cold_ in the head; if it is in the pharynx, it is called a _sore throat_; if it is in the larynx or voice box, there is _hoarseness_; if it is in the bronchial tubes, it is _bronchitis_; finally, if it is in the air cells, it is _pneumonia_. If the air is cut off from access to the air cells, there is an attack of the painful disease called _asthma_, which is accompanied by a feeling of suffocation. Some believe that asthma is caused by the mucous membrane lining the finest bronchial tubes becoming inflamed and swollen, and closing the tubes; others think that the muscles in the large bronchial tubes contract and close the tubes. _Pleurisy_ is inflammation of the pleura and makes breathing painful. If much fluid forms between the pleuras, the inner pleura may press upon the lungs and interfere with breathing. =Alcohol= not only weakens the blood vessels near the surface, but the blood vessels in general. Weakened and congested blood vessels in the lungs make them more liable to pneumonia and other congestive diseases. Continual congestion causes an abnormal growth of connective tissue fiber in the walls of the cells. This diminishes the capacity of the lungs and interferes with the exchange of carbon dioxid and oxygen.