QUANTITY OF GASES RESPIRED. 



227 



Estimation Of Elastic Tension. If a manometer be introduced through an 

 intercostal space into the pleural cavity, in a dead subject, we can measure, by 

 means of a column of mercury, the amount of the elastic tension required to keep 

 the lung in its position. This is equal to 6 mm. in the dead subject, as well as in 

 the condition of expiration. If, however, the thorax be brought into the position 

 of inspiration by the application of traction from without, the elastic tension may 

 be increased to 30 mm. Hg. (Ponders). 



If the glottis be closed and a deep inspiration taken, the air within 

 the lungs must become rarified, because it has to fill a greater 

 space. If the glottis be suddenly opened, the atmospheric air passes 

 into the lungs until the air within the lungs has the same density as 

 the atmosphere. Conversely, if the glottis be closed, and if an expira- 

 tory effort be made, the air within the chest must be compressed. If 

 the glottis be suddenly opened, air passes out of the lungs until the 

 pressure outside and inside the lung is equal. As the glottis remains 

 open during ordinary respiration, the equilibration of the pressure 

 within and without the lungs will take place gradually. During 

 tranquil inspiration there is a slight negative pressure ; during expira- 

 tion a slight positive pressure in the lungs ; the former = 1 mm., 

 the latter, 2 3 mm. Hg. in the human trachea (measured in cases of 

 wounds of the trachea). 



108. Quantity of Gases Respired. 



As the lungs within the chest never give out all the air they contain, 

 it is clear, that only a part of the air of the lungs is changed during in- 

 spiration and expiration. The volume of this air will depend upon the 

 depth of the respirations. 



COMPLEMENTAL 

 AIR, 



110 



TIDAL AIR, 

 20 



BESEEVE AIR, 

 100 



RESIDUAL AIR, 

 100 



t I 



Hutchinson (1846) distinguishes the following 

 points : 



(1.) Residual Air is the volume of air which 

 remains in the chest after the most complete expira- 

 tion. It is equal to 1,230-1,040 c.c. [100-130 cubic 

 inches.] 



(2. ) Reserve or Supplemental Air is the volume 



of air which can be expelled from the chest after a 

 normal quiet expiration. It is equal to 1,240-1,800 

 c.c. [100 cubic inches.] 



(3.) Tidal Air is the volume of air which is 

 taken in and given out at each respiration. It is 

 equal to 500 cubic centimetres [20 cubic inches.] 



(4.) Complemental Air is the volume of air 

 that can be forcibly inspired over and above what 

 is taken in at a normal respiration. It amounts to 

 about 1,500 c.c. [100-130 cubic inches.] 



