PART IV 



THE RESPIRATION 



CHAPTER XXXIV 



RESPIRATION 



For convenience, the physiology of respiration may be considered un- 

 der its mechanics, its control, and its chemistry. 



THE MECHANICS OF RESPIRATION 



Of the many factors concerned in maintaining the normal functioning 

 of the animal body, the respiratory act is probably the most important. 

 On this account and also because we are conscious of the respiratory 

 movements, the physiology of respiration has been studied from the 

 earliest times. Much of the earlier work naturally concerned itself 

 with the study of the air that enters and leaves the lungs at each respi- 

 ration the ventilation of the lungs, as it may be called. Two obvious 

 properties of the respired air are: (1) its pressure and (2) its volume. 



The Pressure of the Air in the Respiratory Passages the Pulmonary 

 - or Intrapulmonic Pressure 



This is readily measured by inserting a tube into one nostril and con- 

 necting the tube with a manometer; at each normal inspiration the 

 manometer registers a negative pressure of 2 or 3 mm. Hg, and at each 

 expiration, a positive pressure of about the same degree. Although 

 normally of small magnitude, the intrapulmonic pressure may become 

 very great when any obstruction is offered to the free passage of the 

 air. The greatest possible expiratory pressure can be measured by sim- 

 ply blowing into a mercury manometer, when it will be equal to that 

 which all the muscles of the thorax and abdomen can exert in compress- 

 ing the lungs. In a strong man it may amount to more than 100 mm. 

 Hg. Similarly, the greatest possible negative pressure on inspiration 

 may be measured by attempting to inspire through a tube connected 

 with a manometer. It represents the force with which the musculature 



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