790 CHANGE OF COMPOSITION OF ALVEOLAR AlR, 



of the deep expirations from wliich the samples were obtained. 

 A complete rest of five minutes was taken after the collection 

 of each sample. The experiments in each series in the Tables 

 given below are recorded in the order in which they were made. 



Two preliminary series of experiments, in which about two 

 hundred analyses were performed, were carried out on two 

 diflferent subjects. In these experiments, attention was not 

 paid to the necessity of allowing the subject to rest completely 

 before taking a sample of alveolar air. The variations among 

 individual experiments were, consequently, too great to allow 

 precise conclusions to be drawn. The average results of each 

 series, however, showed the same features as the experiments 

 recorded here. 



The samples of alveolar air were collected over mercury in 

 exhausted gas-burettes. The deep expirations from the last por 

 tions of which the samples were obtained (Haldane and Priestly, 

 loc. cit.) were made through a brass mouth-piece, 20 cm. long, 

 into a rubber-lined anajsthetic-bag. The mouth-piece was pro- 

 vided with ten side-tubes of capillary bore; to these tubes, burettes 

 were attached. In this way, a number of samples of alveolar 

 air could be collected without other manipulation than the 

 opening of spring-clips. 



The instant at which an expiration was made was recorded 

 on the drum of a kymograph by means of a manometer con- 

 nected witli one of the side-tubes of the mouth-piece. The 

 instant at which respiration was stopped and the holding of the 

 breath commenced, was recorded on the kymograph by pinching 

 the tube leading to the manometer. A Jaquet clock was 

 arranged to make a time-tracing, showing seconds, immediately 

 below the tracing of the manometer. The periods elapsing 

 between the commencement of holding the breath and the 

 making of the expiration from which the sample of alveolar air 

 was obtained, were determined by measurement of the graphic 

 records. In the cases in which the subject breathed into and 

 out of a closed bag, the intervals of time between the successive 

 expirations were measured in the same way. Time could be 

 measured on the tracings with an error of about 0*5 second. 



