CHAPTER XXII 

 THE LUNGS 



.327. Oxidation. Life is a process of oxidation. The 

 body is an engine. The living cells are the machinery, 

 and both they and the blood are the fuel. The fires are 

 lighted at birth, and burn without cessation until death. 



328. Respiration. In every fire a free draft of air must 

 be supplied and the burned products must be carried off. 

 So in the body air must enter continually, and the oxidized 

 products pass out again. The red blood cells are set apart 

 for the special work of carrying oxygen to the rest of the 

 cells of the body, while the lungs are arrangements in 

 which the red blood cells can obtain oxygen from the air. 

 The passage of air into and out of the lungs is breathing. 

 Breathing and oxidation together constitute respiration. 



329. Respiratory organs. An air tube leads from the 

 surface of the body to the lungs. The parts of the tube 

 from the surface to the lungs are the nose, pharynx, larynx, 

 trachea, and bronchi. These parts taken together form the 

 respiratory tract. They, together with the lungs and red 

 blood cells, form the respiratory system. 



330. The nose. The nose is a double tube lined with 

 mucous membrane. Each tube has a smooth bottom and 

 inner wall, but its outer wall is thrown into three curved 

 folds extending lengthwise so as almost to form partitions 

 across the tubes. The folds warm the air and strain out 

 dust as it passes over their surfaces. From each side of 



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