96 Physiology. 



were not for the fact that the descent of the diaphragm 

 meets resistance, and the ribs, in rising, have to overcome 

 resistance in bending the rib cartilages, and in raising the 

 weight of the chest walls and shoulders. 



Potential Energy stored in a Door Spring. When one 

 opens a door that has a spring to shut it, he has to use 

 more force to open the door than he would if he did not 

 have to bend (twist or compress) the spring at the same 

 time. But no effort is needed to shut the door. The door 

 was opened and shut at the same time ; i.e. when the door 

 was opened, force was stored in the spring (in the form of 

 what is called potential energy), and this ^tored energy 

 shuts the door while we pass on. We can better afford to 

 expend more energy while opening the door than to take 

 the extra time to shut it. If, then, a door with such spring 

 were fastened open, it might remain open for a long time. 

 When released it flies shut. If one, in this case, asks, 

 " Who shut the door ? " the answer is, " The person who 

 opened it." 



The Storing of Energy during Inspiration. So in the 



act of inspiration we perform a double work in storing 

 energy by which the expiration is performed without active 

 muscular effort. 



Review of Forces of Respiration : 

 Forces of Inspiration. 



1. Depression of the diaphragm. 



2. Muscles elevating the ribs. 



3. Pressure of the external air. 



Resistances to Inspiration. 



i . Compression of the abdominal organs and stretching abdominal 

 walls. 



