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 peroentile 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.) 



CO 2 analysis 



1st reading of burette 20.00 



2nd reading of burette after absorption of CO 2 19.20 



CO 2 absorbed 0.80 



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 2 + CO 2 in expired air (16.50 -f 4) = 20.50% 



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

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



Since the nitrogen is not changed in volume, 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) X 79 ' 50 (% N 2 in expired air) ; or 0.265 (con- 

 stant factor x 79.5 (% N found for this observation) =21.07, the volume of 2 which 

 would have been present in expired air to account for N present, t 



21.07-16.50 = 4.57% O 2 actually absorbed. 

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

 3.97 

 :. A =0.87, the respiratory quotient, or ratio of CO 2 excreted to O 2 absorbed. 



4.0 / 



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

 fipirometer 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 

 air at and 760 mm. Hg. To do this two things must be taken into account. (1) 

 Since the expired air is saturated with water, the pressure due to water vapor must 



*This is the constant O 2 percentage in air. 



fThis calculation can be simplified by using an abbreviated table (page 597) giving the Og figure 

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



