CHAPTER XIII 



THE MECHANISM AND CHEMISTRY OF RESPIRATION 



IN the preceding chapter we have been following the course 

 by which air passes from the exterior to the innermost cham- 

 bers of the lungs. But 

 the reason air enters 

 and leaves the lungs 

 as we breathe is not 

 explained by merely 

 noting the construc- 

 tion of these passages; 

 for in spite of the va- 

 rious tissues compos- 

 - Sternum i ng them, these tubes 

 are of themselves 

 powerless to inhale 

 even the smalles 

 quantity of air. W< 

 often say "the lunj 

 fill with air"; but we 

 do not appreciate their 

 entire helplessness, 

 their lack of ability to 

 make the least move- 

 ment of their own 

 accord. The lungs 



never fill of themselves; they fill because air is driven 

 into them. 



THE MECHANISM OF RESPIRATION 



Air is drawn into the lungs just as it is into a bellows. 

 When the space inside the bellows is increased air must rush 



txiernaJ 

 Jntercostals 



Internal 

 Intercdsta/s 



> Cartilaye 





FIG. 101. THE ATTACHMENTS OF THE RIBS 



TO THE BACK BONE AND STERNUM 

 To show their relations in breathing. Between one 

 pair of ribs is [shown the external intercostal 

 muscles and between a second pair the internal 

 intercostals, all other muscles being omitted. 



