CHAPTER X. 



EESPIEATOET SYSTEM. 



The organs of respiration consist of the two outer openings, 

 or nostrils (nasal openings) ; the cavities in the head into 

 which they open (nasal cfiambers) ; the cartilaginous box at 

 the head of the windpipe (larynx) ; the long tube called the 

 windpipe (trachea), which is made up of separate rings of car- 

 tilage; its minute divisions into little tubes (bronchial tubes) ; 

 and the lungs, two spongy organs situated in the chest, one 

 on each side, separated by folds of the investing membrane 

 (mediastinum) and the heart; Their office is the purification 

 of the blood by the absorption of oxygen and exhalation of 

 carbonic acid, which takes place in the minute air cells in 

 which the bronchial tubes terminate. The lungs are inti- 

 mately invested by a serous membrane (pleura) similar to 

 that lining the abdomen, which is also reflected over the 

 inner surface of the walls of the chest. This membrane also 

 secretes a humid exhalation to prevent friction during the 

 incessant motion of the lungs. 



This system, from the vascularity of every part of it, is 

 very prone to inflammatory attacks, from a slight coldin the 

 head to violent inflammation of the lungs. 



CATARRH. 



Catarrh, or " cold in the head," is an affection of the lining 

 membrane of the nasal chambers and cavities of the head. 



