870 COMPOSITION OF EXPIRED ALVEOLAR AIR, 



greatest ditt'ereiiee observed in this investigation. Tiie total volume 

 expired in exi3erinient 2 is 1000 c.c, so that the composition of the 

 last 600 c.c. does not vary by more than 0-36% oxygen, and 0*22% 

 carbon dioxide. In experiment 9, which is typical of many, the 

 oxygen has decreased 0'22%, and the carbon dioxide diminished 

 0-16%. 



From these two series of experiments, it appears that the carbon 

 dioxide increases slowly in the expired air during a rapid expira- 

 tion. The rate of increase varies, but, in tlie last 000 c.c. expelled 

 from the lungs, the increase is not more than 0*22% carbon 

 dioxide, while it is not more than half this figure in 17 out of o2 

 experiments. 



Discussiun of lietmlta. — Two methods have been used recently 

 to examine the comp^ition of successive portions of the air 

 expired. Haldane^S) has measured the percentage of carbon 

 dioxide in the linal portion of the air breatlied out during a series 

 of expirations of increasing depth. He has concluded, from his 

 results, that the deeper part of an expiration contahis no more 

 carbon dioxide than the middle part. Krogh and Lindhard(4) 

 have examined successive portions of tlie air breathed out during 

 work, the samples being collected at intervals of some hundredths 

 of a second. They have found that each successive portion of the 

 expired air contains more carbon dioxide than that wljicli precedes 

 it, and less than that which follows it. They have been unable to 

 apply this method to the examination of the breath expired when 

 the body is at rest, but they have employed a modification, whence 

 they conclude that the percentage of carbon dioxide rises slowly 

 at the end of a normal respiration, the curve of the concentration 

 of carbon dioxide in the breath showing a marked tendency to 

 become asymptotic. 



The method used in this paper makes it possible to examine the 

 composition of a part of the air of the same breath to a certain 

 degree of accuracy. When the analysis is made sufficiently deli- 

 cate, it is possible to detect a change in the composition of the 

 final 600 c.c. expelled from the air-passages. The concentration 



