58 THE ORGANS OF SPECIAL SENSE. 



forced respiration, as in pneumonia, where every aid to 

 breathing is called into play, even the alse nasi or nos- 

 trils are made to exert what muscular power they pos- 

 sess 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 sur- 

 face 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 ol/actory 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 con- 

 duction of smell. Hence when one wishes to smell any- 

 thing especially well he sniffs it up. 



Probably the sensation of smell is caused by odorifer- 

 ous 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- 



