94 PHYSIOLOGY. 



afford to employ 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. 



1. Compression of the abdominal organs and stretching 

 abdominal walls. 



2. Bending the rib cartilages and lifting the chest. 



3. Stretching the lungs. 



ELASTIC REACTIONS OF EXPIRATION. 



1. Elastic reaction of the abdominal walls and contents. 



2. Elastic reaction of the rib cartilages. 



3. Elastic reaction of the lungs. 



Forced Respiration. Thus far we have been speaking 

 of ordinary respiration. In forced respiration, as in shout- 

 ing, many muscles are brought into play to expel the air 

 rapidly and forcibly. In such an act as coughing there is 

 vigorous action of the abdominal muscles. 



