BY ETHEL C. PINKERTON. 871 



of carbon dioxide increases by a variable amount in different 

 experiments, but never more than 0-22%, while tlie increase can 

 liardly be detected in some experiments. The percentage of 

 oxygen diminishes by not more than 0'36%. 



In considering which of these methods yiehls tlie most correct 

 information as to the composition of the expired air, it may l)e 

 noted that Haldane's experiments have been made on different 

 respirations. His method of estimating carbon dioxide has been 

 sufficiently accurate to detect the change of composition, but the 

 fact that he obtained his samples at various depths of respiration 

 from different breaths has not permitted him to recognise small 

 differences in concentration. Krogh observed the change of con- 

 centration during work by analysis of successive samples collected 

 at consecutive intervals of time, but, for conditions of rest, his 

 curve was mainly the result of interpolation. In the method 

 employed in this investigation, the analyses are made on successive 

 portions of the same respiration. When the gaseous analysis has 

 only been capable of recognising the change of concentration of 

 0*2% in the amount of carbon dioxide, the composition of the 

 final 600 cc. expired has appeared uniform; but, with greater 

 delicacy, a change in concentration of not more than 0-22% of 

 carbon dioxide, and 0*36% oxygen has been observed. 



Tliese results are in accord with the results of Krogh and Lind- 

 hard. They support Lindhard's contention (4), that the final 

 portion of the expired air has not the same composition as the air 

 in the alveoli of of the lungs, since the portion of the alveolar air 

 in the trachea and bronchioles will contain more carbon dioxide, 

 than the air expelled from the mouth, as it leaves the alveoli later. 



Conclusions. 

 (1) Estimations of the percentage of oxygen and carbon 

 dioxide in the successive portions of air rapidly expelled from the 

 lungs, show that the concentration of carbon dioxide diminishes 

 by not more than 0'22% in the final 600 cc, respired, and that 

 the concentration of oxygen augments by not more than 0*36^ 

 in the same portion of the breath. 



