THE LUNGS. i;i 



17. The Lungs lie inside the thorax, one on each side 

 of the heart (Fig. 2). They are elastic spongy masses, 

 full of tiny cavities, named air-cells. Into the air-cells 

 the smallest bronchial tubes open (Fig. 45). Thus air 

 gets to them, ready to give 



oxygen to the blood, and carry 

 off carbonic acid from it. 



18. Inspiration and Expira- 

 tion. Breathing consists of 

 breathing-in and breathing- 

 out, turn and turn about. 

 Breathing-out gets rid of air 



Which has become foul in the Magnified about twenty times. 



lungs: it is named expiration. Breathing-in conveys new 

 air to the lungs in place of that which has been expired: 

 it is known as inspiration. 



19. The Movements of the Chest alternately enlarge 

 and diminish its cavity. When it is enlarged, air enters 

 it ; when it is diminished, air is driven out. We may 

 compare the chest in this respect to a pair of bellows. 

 The chief difference is that air enters the bellows through 

 one aperture, and is driven out through another ; while 

 in breathing, air comes and goes by the same road, the 

 windpipe, which answers to the nozzle of the bellows. 



20. How the Chest- Cavity is Enlarged to cause Inspira- 

 tion. The enlargement of the chest is brought about 



17. Position of the lungs? Structure? How does air reach the 

 air-cells of the lungs ? 



18. Of what does breathing consist? Use of breathing-out? Its 

 technical name ? Of breathing-in ? Its technical name ? 



19. Result of the chest - movements ? What happens when the 

 chest is enlarged ? Diminished ? Illustrate. What part of the re- 

 spiratory organs corresponds to the nozzle of a pair of bellows ? 



20. How is the chest enlarged ? Position of the ribs in expiration? 



