THE ALVEOLAR AIR OF THE LUNGS 



541 



dioxide in the alveolar air varied inversely as the atmospheric 

 pressure, so that the pressure of the alveolar carbon dioxide was 

 constant. The pressure of oxygen, on the other hand, showed 

 great variations. The following table gives the mean results 

 obtained for the alveolar air at different pressures ; the per- 

 centages of oxygen were calculated on the assumption that the 

 respiratory quotient was 0-85. 



During muscular work there is a rise of about 0-285 per cent, 

 in the alveolar carbon dioxide ; this will be discussed in con- 

 nection with the question how the respiratory movements are 

 regulated in depth and frequency. 



The limits within which the pressure of carbon dioxide varies 

 in the alveolar air of different individuals have been investigated 

 by FitzGerald and Haldane ( 22 ). The following table (see p. 542) 

 shows the mean and the range of the pressures of carbon dioxide. 



Direct determinations of the air of an occluded portion of 

 the lungs were made on animals by Pfliiger and his pupils. For 

 the collection of this air a special form of catheter, the lung- 

 catheter, was used. It consists of a fine elastic catheter, sur- 

 rounded, except at its extremities, by a tube with a rubber 

 enlargement towards the free end of the catheter. It can be 

 introduced through the trachea into a bronchus of a dog with- 

 out preventing the free passage of air in and out of the other 

 portions of th.3 lungs. When the catheter is in position, the 

 rubber enlargement is inflated, and thus shuts off a portion 

 of the lungs from which the alveolar air can be withdrawn 



