150 ANATOMY AND PHYSIOLOGY FOR NURSES 



pulmonary ventilation: (i) The residual air, or that part 

 that cannot be expelled from the lungs, but remains after 

 a full and forcible expiration, averages 120 cubic inches; 

 (2) the supplemental or reserve air, or that which can be 

 expelled by forcible expiration after an ordinary out- 

 breathing, measures 130 cubic inches; (3) the breath, 

 tidal or breathing air, averages 26 cubic inches; (4) the 

 complementary air, or that which can be inhaled after an 

 ordinary inspiration, measures 100 cubic inches. Thus, 

 this estimate gives 250 cubic inches as the average volume 

 of air that the lungs contain after an ordinary inspiration. 



From what has been said it is apparent that the blood 

 is constantly exposed to the air in the lungs ; and it would 

 appear that the residual air, or that which remains in the 

 lungs after the expiration, is most exposed to the affinities 

 in the materials of the blood, and, in all probability, it is 

 upon this portion that the greatest impression is made. 

 The inspiration replaces this residual air by admixture 

 with the fresh portions inspired, and some of the expira- 

 tions remove the mixed air so formed. 



Many experiments have been tried to determine the 

 amount of change of air in the lungs produced by a single 

 breath. From the nature of the problem no method is 

 wholly satisfactory. The one originally proposed by 

 "Davy" is given by Prof. N. Kuntz, of Leipzig. It 

 consists of inhaling a known volume of pure hydrogen, 

 and then analyzing the expired air. If no mixing of the 

 hydrogen with the air already in the lungs takes place, then 

 the expired gas, like the inspired, would be pure hydro- 

 gen. By actual experiment it is found that, supposing 

 that 500 c.c. of pure hydrogen are inhaled, only 170 c.c. 

 of the hydrogen are exhaled, the remaining 330 c.c. being 

 air. That is, 330 c.c. of the inhaled hydrogen displaces 

 the same amount of air. If, now, it is assumed that in 

 ordinary breathing 500 c.c. of air are inhaled, and 330 c.c. 



