COMPOSITION OF THE AIR DURING RESPIRATION. 755 



a given time, not by a calculation based upon the alteration in the com- 

 position of the air of several expirations, multiplied by the average 

 quantity of expired air and the average number of respirations in a 

 given time. 



Vierordt 4 concluded from his experiments that the percentage of 

 carbon dioxide in the expired air diminished, but the total discharge 

 increased when the respiration was voluntarily quickened, the depth of 

 breathing remaining the same, 500 c.c. ; similar effects were produced by 

 breathing more deeply but with the same frequency. The drawback to 

 these observations is that they were for periods only lasting two or 

 three minutes, and thus they are no exact measure of changes of meta- 

 bolism. Even the extended observations of Lossen and Berg have been 

 the subject of much discussion and criticism between Pfliiger 5 and 

 Voit. 6 It is impossible here to go fully into the causes of some of the 

 contradictory results, but Pfliiger appears to have shown that the 

 variations in the breathing have no influence upon the respiratory 

 metabolism beyond this, that when the respiratory muscles are more 

 active, an extra amount of metabolism, due to this activity, will occur. 

 Pfliiger takes the mean of the conflicting results and obtains the 

 following suggestive figures : 



Carbon dioxide discharged in fifteen minutes 



1 Arch. d. Ver.f. tvissensch. ffeilk., Leipzig, 1867, Bd. iii. S. 317. 



2 "Physiologic des menschlichen Athmens," Leipzig, 1892 ; Arch. f. Physiol., Leipzig, 

 1896, S. 465. 



:! Arch.f. d. ges. Phijsiol., Bonn, 1888, Bd. xliii. S. 523, et scq. 



4 Hesse, Arch.f. ffyg., Munchen u. Leipzig, 1884, Bd. ii. S. 381; "Physiol. d. 

 Athmens," Karlsruhe, 1845, S. 116, 134. 



5 Arch.f. d. ges. Physiol., Bonn, 1877, Bd. xiv. S. 1, 630. 



6 Ztschr. f. JBioL, Munchen, 1878, Bd. xiv. S. 95. 



