RESPIRATION 39 



sure above the diaphragm is slightly less than the atmos- 

 pheric pressure and consequently than the pressure 



A B 



Fig. 26.— Diagram to show the position of the sternum, diaphragm and abdominal 

 Wall in A, inspiration and B, expiration. The shaded area represents the 

 stationary air, the unshaded area in A, the increased air space in inspiration. 



below it. This causes the peculiar behavior of the dia- 

 phragm in hanging upward. 



Phraseology — The word respiration is used some- 

 times to refer to inspiration and expiration, and some- 

 times to the passage of gases through a membrane. To 

 prevent confusion the passage of gases through a mem- 

 brane has been called internal respiration, and the move- 

 ment of the chest external respiration, but it seems 

 clearer to restrict the word respiration to the essential 

 process that occurs in all animals and reserve the words 



