CHAPTER XIII 



A PAIR OF LIVING BELLOWS 



Often in former chapters, especially when describing the 

 muscular engines and the heart or blood-pump or the 

 human machine, we had occasion to mention how oxygen 

 was carried to them by the microscopic red discs of the 

 blood. If oxygen is withheld, the muscular engines and 

 pump are not only unable to work but perish almost 

 immediately. So far not a word has been said of how 

 the red blood discs come by their loads of oxygen. This 

 is the subject upon which we now enter. Here again, 

 we shall find that Nature has adopted a kind of machine 

 which man has also discovered and used for many 

 purposes, namely, the bellows. Our chest or thorax is 

 really a pair of bellows ; there is a windpipe or trachea, 

 just as the bellows has an air-pipe ; at the end of the pipe 

 is fitted a nose or nozzle. The human pair of bellows 

 are lined by two much-folded membranes — the lungs. 

 Within the lungs, which line the thorax or bellows, are 

 air chambers. It is from these air chambers that the red 

 blood discs pick up their loads of oxygen. 



We are so familiar with the movements of the bellows 

 of the human machine that we never give them much 

 attention. They go on by themselves morning, noon, and 

 night ; we have not to trouble about them, because they 

 are managed for us. Even if we do try to stop or alter 

 their actions, we have discovered long ago that their 

 control is quickly snatched from us. With an effort we 

 may bring our wills into action and stop them for sixty 

 seconds or even more, but at the end of that time some 



