CHAPTER XIV 

 RESPIRATION 



252. Definition. The lymph obtains from the blood in 

 the capillaries and conveys to the tissues all that they 

 need for sustaining their life. Their waste products are 

 returned to the blood. One important element which all 

 the tissues need, is oxygen, and one important element in 

 the waste is carbon dioxide, or carbonic acid gas. 



Respiration is the process by which oxygen is supplied 

 to the blood and an excess of carbonic acid is removed from 

 it. As a general term, respiration includes also the inter- 

 change of these gases in the tissues, called internal respi- 

 ration, or tissue respiration, but the word is more com- 

 monly restricted to that part of the process which takes 

 place in the lungs. 



253. The Respiratory Apparatus consists of the channels 

 through which air passes to reach the capillaries of the 

 lungs, viz. nostrils and mouth, pharynx, larynx, trachea, 

 bronchi, bronchial tubes, alveoli, and air cells ; together 

 with the muscles of the chest, of the diaphragm, and of 

 the abdomen. 



254. Normally the air enters the pharynx through the 

 nostrils rather than the mouth. By passing through the 

 winding passages of the nose it acquires nearly the tem- 

 perature of the body, and is also relieved of some of the 

 particles of dust always floating in the atmosphere. 



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