868 



COMPOSITIOX OF EXPIRED ALVEOLAR AIR, 



Table ii. 



The results are arranged in the order of the volume of the 

 expired air. The expired air has been ejpelled as quickly as pos- 

 sible from tlie lungs. The brass tube contains 625 c.c. between the 

 mouthpiece and the outlet, 200 cm. from tlie mouthpiece. The 

 results show that the air, filling the brass tube, in the neighbour- 

 hood of the outlets at 25 cm., and 50 cm., invariably contains 

 slightly less oxygen, and slightly more carbon dioxide than that in 

 the neiglibourhood of the outlets at 17.") cm., and 200 cm., from 

 the mouthpiece. The difference in experiment 9 amounts to less 

 than 0*07% oxygen, and to less than 0*04% carbon dioxide; 

 while, in experiment 7, the difference amounts to 0*02% oxygen, 

 and to 0*15% carbon dioxide, the greatest difference observed 

 in this series. It would thus appear that, in a respiration of about 

 1300 c.c, the last 625 c.c. show a change in composition of not 

 more than 0-15% carbon dioxide, and 0'20% oxygen. The range 

 of variation in the composition of the last 625 c.c. to be expelled 

 from the lungs depends on the sjDeed with which the air is driven 

 into the brass tube. The quicker the air enters, the more uniforni 

 is the composition of the last portion. As the period of expira- 

 tion becomes prolonged, the percentage of carbon dioxide in the 

 last part of the expired alveolar air rises, while the percentaoe of 

 oxygen falls {vide experiment 4 of Table iii.). 



