596 METABOLISM 



The oxygen is removed by a similar procedure, the gas being passed into the alkaline 

 pyrogallate solution by turning cock 8 to communicate with bulb 12. The absorption 

 of oxygen is slower than for CO 2 , and more care must be taken to get complete 

 absorption. The air in the tubing between the fluid in 9 and stopcock 8 must be 

 washed out several times in order to get the oxygen which is left in it after the 

 absorption of the CO 2 . When this is complete, the final reading on the burette is 

 made and the loss in volume from the second reading represents the oxygen. 



THE CALCULATIONS 



The calculation of the percentage composition of the air and of the respiratory 

 quotient is represented in the following example of an actual analysis: 



(The temperature and barometric pressure as taken at the time of the experiment 

 were 20 C. and 747 mm. Hg.) 



C0 2 analysis 



1st reading of burette 20.00 



2nd reading of burette after absorption of CO 2 19.20 



CO 2 absorbed O80 



0.80 -^- 20 = 4.0 per cent CO 2 in expired air. 



2 analysis 



2nd reading of burette 19.20 



3rd reading of burette after absorption of O 2 15.90 



O 2 absorbed 3^30 



3.30 -f- 20 = 16.50 per cent of 2 in expired air. 



Determination of E.Q. 



O 2 in atmospheric air = 20.94% 



O, + CO 2 in expired air (16.50 -t- 4) = 20.50% 



100 - 20.94* = 79.06%, N in atmospheric air. 

 100-20.50 =79.50%, N in expired air. 



Since nitrogen is an inert gas in the body, the last figure shows that more oxygen 

 must have been taken in during inspiration than O 2 + CO 2 has been given back in expira- 

 tion. This obviously must be taken into account in the calculations. The amount of 

 O 2 actually inspired for each 100 c.c. of air expired is found as follows: 



20.94 (% O 2 in atmospheric air) 



79.06 (% N 2 in atmospheric air) < 79 ' 50 <% N * in ex P ired air ) >' or ' 265 ( con ' 

 stant factor) X 79 - 5 21.07.f 



The amount of O 2 actually absorbed by the animal is therefore: 



21.0716.504.57%. 

 and the amount of CO 2 excreted is: 



4.00 - 0.03 (CO 2 in inspired air) 3.97 % CO 2 . 

 The respiratory quotient, or ratio of CO 2 excreted to O 2 absorbed is therefore: 



3.97 

 _ =0 .87. 



Total Gas Exchange. The volume of air expired in 15 minutes into the Tissot 

 spirometer was found to be 100 liters measured at 20 C. and 747 mm. Hg. (brass-scale 

 barometer). This volume of gas must be corrected so as to give the volume of dry 





*This is the constant Oa percentage in air. 



tThis calculation can be simplified by using an abbreviated table (page 597) giving the O 2 figure j 



corresponding to the various percentages of N in the expired air. 



