BY ETHEL C. PINKERTOX. 



147 



that physiologists accepted the possibility of ascei-taiiiing, with 

 some approach to accuracy, the composition of alveolar air. This 

 method was of great simplicity. The breath was forcibly ex- 

 pelled through a long rubber tube connected with the mouth, 

 and the end of tlie tube at the mouth was closed with the tongue 

 at the termination of the act of expiration. By means of an 

 inlet in the side of the tube close to the mouth, a sample of the 

 last portion of the expired air could be withdrawn from the tube 

 for analysis. This sample was held to be of the same composi- 

 tion as the alveolar air. In order to obtain the mean composi- 

 tion of the alveolar air, the breath was expelled at the close of a 

 normal inspiration, and later at the end of a normal expiration. 

 The mean of the analyses of the last part of these two samples 

 was considered to represent the average composition of the gases 

 of the alveoli. The proof of the nature of the last portion of the 

 air driven out of the lungs in a forced expiration, consisted of 

 analyses of the samples collected after the expulsion of different 

 quantities of expired air. Haldane considered that, if any of 

 the relatively pure air filling the bronchial tubes of the lungs, 

 was mixed with the last part of the air of the sample, there 

 would be a higher concentration of carbon dioxide in the sample 

 collected from a deep expiration than would be present hi the 

 sample taken after an ordinary expiration. He gave the results 

 obtained from an experiment in which four samples were col- 

 lected after sharp expirations of varying depths immediately 

 following the completion of inspiration. The amount of 

 expired air breathed out, by the subject of this experiment, as 

 tidal air, had been found previously to measure 600 c.c. The 

 figures of the analyses of the samples taken under these con- 

 ditions are given in Table i. 



Table i. 



