BY ETHEL C. PIXKERTON. l.")9 



as possible by the subject (time of expiration ascertained to be 

 two seconds for the deep expiration, and one second for the 

 shallow expiration), but in one experiment (1), the expulsion 

 occupied two seconds. 



The results show that, when the expulsion was made rapidly 

 in the times mentioned above, the last portions of the expired 

 air contained a similar percentage of carbon dioxide. When, 

 however, the expiration was less rapid, the successive samples 

 showed an increase in concentrations of carbon dioxide. 



The time occupied in breathing out various amounts of air as 

 quickly as possible from the lungs was found approximately with 

 the aid of a stop-watch. The figures obtained from sixty experi- 

 ments, in which the time was noted, are: — 



For lOUOc.c. expired, the average 0*o sec, max, O'G.sec., iiiin. 0"4 see. 



For 1200c.c. expired, the average '6.5 sec., max. 0.8 see., min. O'osec. 



For l.KXIc.e. expired, the average 1"1 sees., max. I'osecs., min. 0'9sec. 



For ISOOc.c. expired, the average 1 '9 sees., max. '2'2secs., mil). I "8 sees. 



For 2()00c.e. expired, the average 2"0sees., max. 2*.j sees., min. 1 '4 sees. 



For 2200 c.c. expired, the average 2"o sees. 



A study of a graph constructed from these figiu^es shows that, 

 after loOOc.c. had been expelled from the lungs, the rate of 

 expulsion became distinctly slower; and that the speed of expul- 

 sion was approximately diminished to one-half its former value. 



BiscHssion. — These results, which are confirmed by those with 

 two other subjects, show that the last air expired is of uniform 

 composition within the error of analysis, provided that the ex- 

 piration was made quickly. When the total ex23ired air 

 amounted to one litre, the last 625 c.c. contained a uniform per- 

 centage of carbon dioxide after the air had been expelled from 

 the mouth in less than one second. It would thus appear that 

 this last 625 c.c. was not mixed with any part of the air of the 

 "dead space." While it is no doubt true that the percentage of 

 carbon dioxide in the puhnonary air-cells is continuously increas- 

 ing during the expiratory phase, it is not possible, when the 

 subject is not doing heavy work, to obtain any evidence of an 

 increase in the percentage of carbon dioxide during a deep, 



