150 CARBON DIOXIDE IX EXPIRED ALVEOLAR AIR, 



111 a critical examination of the methods for measuring the 

 ^uk^neof the "dead space", Henderson, Chilhngworth and Whit- 

 ney (10) determined the composition of successive portions of the 

 expired air. They found that the concentration of carbon dioxide 

 in the expired air increased in each successive portion expelled 

 from the air-passages. Their experiments ceased when the 

 volume of expired air amounted to 400 c.c, possibly because they 

 Avere conceined with tidal respiration, and did not wish to pro- 

 duce dilatation of the small bi'onchioles by forcible expiration. 

 They state that 400 c.c. are sufficient to remove the whole of the 

 air from the "dead space", and that the final samples of expired 

 air consisted of undiluted alveolar air. Their published curve 

 shows, however, that the concentration of carbon dioxide was 

 still rising when their experiments ceased. To this j^ublication, 

 Haldane(ll) appended a paper, in which he discussed again the 

 evidence in support of the determination of the ccnnposition of 

 alveolar air by the method of 1905. He stated that "it now 

 appears that the air of constant carbon dioxide pressure is 

 alveolar air from the 'air-sacs' of Miller's nomenclature, and that 

 the air from the alveoli of the 'atria' is of a different and more 

 variable composition." A series of 17 analyses was given to 

 extend the observations on the concentration of carbon dioxide 

 after the expiration of different amounts of air. The average 

 figures are published in a table, reproduced as Table ii. 



Table ii. 



Depth of respiration. 



190 

 33o 



650 



9o0 



1350 



Percentage of COo in air issuing 

 from the mouth. 



3 03 

 4-37 

 5 04 

 5-19 

 5'51 

 5-48 



In k further series on a different day, the results of six suc- 

 cessive determinations gave the mean percentage of carbon 

 dioxide as 5*39 with an expiration of 900 c.c, and 5' 36 with an 



