12 SCIENCE OF BREATH. 



into the trachea or windpipe, which subdivides into numer- 

 ous tubes called the bronchial tubes (bronchia), which in 

 turn subdivide into and terminate in minute subdivisions 

 in all the small air spaces in the lungs, of which the lungs 

 contain millions. A writer has stated that if the air cells 

 of the lungs were spread out over an unbroken surface, 

 they would cover an area of fourteen thousand square feet. 



The air is drawn into the lungs by the action of the 

 diaphragm, a great, strong, flat, sheet-like muscle, stretched 

 across the chest, separating the chest-box from the ab- 

 domen. The diaphragm's action is almost as automatic as 

 that of the heart, although it may be transformed into a 

 semi-voluntary muscle by an effort of the will. When it 

 expands, it increases the size of the chest and lungs, and 

 the air rushes into the vacuum thus created. When it 

 relaxes the chest and lungs contract and the air is expelled 

 from the lungs. 



Now, before considering what happens to the air in 

 the lungs, let us look a little into the matter of the circula- 

 tion of the blood. The blood, as you know, is driven by 

 the heart, through the arteries, into the capillaries, thus 

 reaching every part of the body, which it vitalizes, nour- 

 ishes and strengthens. It then returns by means of the 

 capillaries by another route, the veins, to the heart, from 

 whence it is drawn to the lungs. 



The blood starts on its arterial journey, bright red 

 and rich, laden with life-giving qualities and properties. 

 It returns by the venous route, poor, blue and dull, being 

 laden down with the waste matter of the system. It goes 

 out like a fresh stream from the mountains; it returns as 

 a stream of sewer water. This foul stream goes to the 

 right auricle of the heart. When this auricle becomes 

 filled, it contracts and forces the stream of blood through 

 an opening in the right ventricle of the heart, which in 

 turn sends it on to the lungs, where it is distributed by 

 millions of hair-like blood vessels to the air cells of the 

 lungs, of which we have spoken. Now, let us take up the 

 story of the lungs at this point. 



The foul stream of blood is now distributed among the 

 millions of tiny air cells in the lungs. A breath of air is 



