ALTERATIONS OF AIR IN THE LUNGS 



is consumed, the total amount necessary for an hour will be 

 about 1,100 cu. in. This allows, however, for no muscular, 

 digestive or other activity, and the amount actually necessary 

 is larger than this. 



The circumstances which call for an increase in O almost 

 invariably cause an increase in the output of C(X 



(b) Gain of Carbon Dioxide. The amount of CCte in in- 

 spired air is about .04 part per hundred (fioo per cent.) ; the 

 amount in expired air is something more than 4 parts per 

 hundred. In round numbers then, the air in passing through 

 the lungs gains of CO2 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, mois- 

 ture, 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 ra- 

 pidity of respiration is increasing, the depth remaining con- 

 stant, the percentage of CCte 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 in- 

 creased depth and a constant rate. With a diminished ra- 



