CHAPTER IX. 



THE LUNGS AND THE PROCESSES OF 

 RESPIRATION. 



The circulation of the blood treated in the preceding 

 chapter leads naturally and without a break to the consider- 

 ation of the phenomena of respiration. It was pointed out 

 that the main reason for the mad rush of the blood is to 

 carry out the functions of respiration. Respiration consists 

 essentially in two gaseous interchanges. One of these takes 

 place in the lungs. Here oxygen is taken up by the red 

 corpuscles and carbon dioxide thrown off from the plasma. 

 The second gaseous interchange occurs in the tissues of the 

 body and is the exact reverse of the first, for here the 

 oxygen is liberated and the carbon dioxide picked up. 



These two respiratory interchanges are complementary. 

 The one in the lung is called external respiration, the one 

 in the tissues internal respiration. We are first concerned 

 with the processes as they take place in the lungs. 



THE ANATOMY OF THE RESPIRATORY SYSTEM. 



The principal structure concerned in external respir- 

 ation is the lung. Into this air is drawn through the mouth 

 and nostrils by way of the trachea. At the upper portion 

 of the trachea where it leads into the pharynx is a dilata- 

 tion called the " voice-box." Here by suitable arrange- 

 ments the outgoing air sets into vibration stretched mem- 

 branes which produce the sounds of speech. For a detailed 

 description of this organ, the voice-box, or larynx, the 

 student is referred to a subsequent chapter on "The Voice. ' ' 



The windpipe, or trachea as it is called, may be easily 

 felt by placing the finger on the throat. The large dilated 

 portion is the voice-box just noted, while the tube extend- 

 (202) 



