CHAPTEK XV. 

 DISEASES OF THE RESPIRATORY SYSTEM. 



NOSE AND NASO-PHARYNX. 



Rhinitis. The air which is inspired through the anterior 

 nares, across the nasal cavities, and by the posterior nares into 

 the naso-pharynx, is passed over a large surface covered with 

 mucous membrane. This membrane secretes mucus upon which 

 should be deposited all solid particles, including bacteria, floating 

 in the air ; hence the liability of the upper part of the respira- 

 tory tract to infection and inflammation. This power of the 

 nasal mucous membrane to catch undesirable material is very 

 well demonstrated in towns during a fog. 



The many accessory air cavities communicating with the nose 

 may one or all become the site of infection by extension. The 

 infundibulum, ending in the middle meatus, passes upwards into 

 the frontal sinus, and the frontal headache so frequently present 

 with a " cold in the head " indicates inflammation of the mucous 

 membrane lining this air cavity. From the middle meatus, also, 

 micro-organisms may pass through the small aperture into the 

 antrum of Highmore, and may occasionally give rise to an 

 empyema therein. The posterior ethmoidal and sphenoidal 

 sinuses are sometimes infected through their openings into the 

 superior meatus. 



It is worthy of notice, also, that infection may pass directly 

 along the branches of the olfactory nerves, through the cribriform 

 plate of the ethmoid bone, into the interior of the cranium, there 

 to set up a septic meningitis. In like manner the thin bony 

 walls of the ethmoidal and sphenoidal sinuses may be eroded, 

 and the overlying dura mater attacked. 



The close proximity of the cranial cavity to the nasal fossae 



