ALTERATIONS OF AIR IN THE LUNGS 



in expired air is something more than 4 parts per hundred. In 

 round numbers then, the air in passing through the lungs gains 

 of CO 2 4 per cent, of its entire volume. This is in periods of 

 rest from exercise, digestion, etc. The total amount discharged 

 in one hour is, on an average, about 1,000 cu. in. This estimate 

 should probably be raised to 1,200 cu. in. for ordinary activity, 

 and varies according to many conditions, some of which are 

 rapidity and depth of respiration, age, sex, digestion, diet, sleep, 

 exercise, moisture, temperature, season, integrity of the nerve 

 supply, etc. 



The subjoined table from Kirkes' Physiology compares the 

 composition of inspired and expired air. 



Conditions Influencing Output of CO 2 . When the rapidity of 

 respiration is increasing, the depth remaining constant, the 

 percentage of CO 2 in the expired air is reduced because more air 

 is respired, but the total quantity in any given time is increased. 

 The same result follows an increased depth and a constant rate. 

 With a diminished rapidity and increased depth more CO 2 is 

 exhaled than under opposite conditions. 



The amount of CO 2 exhaled is small in very young infants. 

 But soon the output begins to increase, and in males continues 

 to do so up to about thirty years; there is then a slight decrease up 

 to sixty, and afterward a considerable decrease to death. 



In the female the output is less than in the male. In the former 



