CHARACTER AND COMPOSITION OF AIR 



299 



must be considered approximate only, inasmuch as various circumstances, 

 even in health, influence the amount of carbon dioxide excreted, and, cor- 

 relatively, the amount of oxygen absorbed. 



The total amount of carbon dioxide excreted is influenced sharply by a 

 number of factors: First, the depth and volume of respiratory movements. The 

 greater the volume of air breathed, the greater the total output of carbon 

 dioxide, though the percentage per unit of 

 expired air is decreased. This influence de- 

 pends upon the more efficient oxidative 

 processes in the presence of more thorough 

 ventilation of the lungs and blood. Second, 

 the carbon dioxide output varies with age. 

 It is greater with children and youth than 

 with the old. In extreme old age the total 

 output may not exceed that of the ten-year- 

 old child. Third, there is a diurnal variation 

 in carbon dioxide output. The respiratory 

 quotient, i.e., the ratio between carbon 

 dioxide eliminated and oxygen absorbed, is 

 greater during the day than during the 

 night. In the day, therefore, the carbon 

 dioxide exhaled in relation to the oxygen 

 absorbed is increased, and it is diminished 

 during the night. This is probably due to 

 the increased production of carbon dioxide 

 as a result of increased tissue activity during 

 the day, and, consequently, the breaking 

 down or katabolism of more substances. 

 Fourth, the character and quantity of the 

 food greatly influence the proportion of 

 carbon dioxide as indicated by the respira- 

 tory quotient. It is greater with carbohy- 

 drate foods. During fasting there is for the 

 first two or three days an increased carbon 

 dioxide output, but later this is decreased. 

 Fifth, the bodily exercise, in moderation, 

 increases the quantity of carbon dioxide ex- 

 pired by at least one-third more than it is 



during rest. For about an hour after exercise the volume of the air expired 

 in the minute is increased nearly 2,000 cc., or 118 cubic inches; and the 

 quantity of carbon dioxide about 125 cc., or 7.8 cubic inches per minute. 

 Violent exercise, such as full labor or athletic competition, still further in- 

 creases the amount of the carbon dioxide exhaled. Sixth, the observations 

 made by Vierordt at various temperatures between 3.4-23.8 C. (38 F. 

 and 75 F.) show, for warm-blooded animals, that within this range every 

 rise equal to 5.5 C. (10 F.) causes a diminution of about 33 cc. (2 cubic 

 inches) in the quantity of carbon dioxide exhaled per minute. 



The Volume of the Respired Air is Diminished. When allowance has 

 been made for the expansion in heating, the volume of expired air is decreased, 



FIG. 236. Apparatus for Esti- 

 :> 2 and CO 2 in Expired 



