Page:Structure and functions of the body; a hand-book of anatomy and physiology for nurses and others desiring a practical knowledge of the subject (IA structurefunctio00fiskrich).pdf/64

 forced respiration, as in pneumonia, where every aid to breathing is called into play, even the alæ nasi or nostrils are made to exert what muscular power they possess in order to supply more air.

Not only is most of the air breathed in through the nose and warmed in its passage through, but the nose is the organ of smell and by means of the peculiar property of its nerves protects the lungs against deleterious gases and helps the taste discriminate. The olfactory or ''first cranial nerves'', after emerging from the brain, lie on the under surface of the frontal lobe and rest on the ethmoid bone in what is known as the olfactory tract. Each nerve ends in a bulb-like termination called an olfactory bulb, which rests on the cribriform plate and sends little terminal fibers down through to be distributed to the nasal cavities, especially to the upper half of the septum of the nose, the roof of the nose, and the anterior and middle turbinated bones. For in the mucous membrane of the upper nasal cavity are specially modified epithelial cells called olfactory cells, which play an important part in the conduction of smell. Hence when one wishes to smell anything especially well he sniffs it up.

Probably the sensation of smell is caused by odoriferous particles in the atmosphere being breathed into the nose, where they affect the olfactory cells, which transmit the impulses to the olfactory nerve and so to the brain. Whereas a certain amount of moisture in the nasal cavity seems to be essential for accuracy of smell, the presence of too much or too little interferes with it. The mucous membrane has a certain power also of distinguishing different smells at the same time, though this power varies greatly in different people, one smell often wholly overpowering all others.

The cartilage below the bridge of the nose is sometimes attacked in syphilis and cancer, and lupus often begins on the nose. Deviation of the septum may occlude all air from one side of the nose, an effect also produced by polypi, generally of the turbinated bone. Either condi