BY ETHEL C. PINKERTON. l5l 



expiration of 1750 c.c. Haldane concluded that the deeper part 

 of the expiration contained no more carbon dioxide than the 

 middle part. 



Sco2)e of Research. — The experiments to be described in tlie 

 present paper are designed to estimate the percentage of carbon 

 dioxide in successive porticjns of expired air. They were under- 

 taken in consequence of repeated failures in the Physiological 

 Laboratory to obtain any close agreement in the concentration 

 of carbon dioxide in different samples of alveolar air, collected 

 after the method of Haldane and Priestley. Instead of observing 

 any constancy in these values, even when averaged results were 

 obtained of five samples taken at the close of inspiration, and of 

 five taken at the close of expiration, as described by H. G. 

 Chapman (12), the values obtained showed variations of 5% or 

 even more. It became necessary to ascertain whether the \>ev- 

 centage of carbon dioxide increased in the last 600 c.c. of air 

 expressed from the air-passages in a forcible expiration. 



The air issuing from the mouth was passed along a brass tube 

 of sufficient length to accommodate the greater part of the ex- 

 pired air. The mouthpiece was of such a size and shape as to 

 be closed readily by the lips, so that the whole of the air dis- 

 charged from the air-passages entered the tube without admix- 

 ture with the atmosphere. At the conclusion of the expiration, 

 the mouthpiece could be securely shut by the tongue. The ex- 

 pired air was collected from different subjects and under varying 

 conditions. As a rule, no attempt was made to get uniform 

 results by resting in a chair for some minutes with regular 

 l)reathing. The air was expelled forcibly, sometimes at the end of 

 inspiration, and sometimes at the end of expiration, sometimes 

 after shallow breathing, and sometimes after several deep breaths. 

 As it was only desired to know how the percentage varied in 

 the successive parts of the later portions of the expired air, it 

 became unnecessary to pay attention to these factors, when it 

 was found that none of them caused any variation in the char- 

 acter of the results. Small, metal, capillary tubes inserted into 

 the sides of the brass tube served for withdrawing samples foi* 



