BY ETHEL C PINKERTON. 



15: 



later from the mouth. In these three experiments, the difi'erence 

 in composition is so slight as not to be detectable with certainty 

 by the method of analysis. If Tables v. and vi. be compared, it 

 will be seen that there is a decided change in the results. When 

 the quantity of air expelled from the mouth was over two litres, 

 the amount of carbon dioxide in the tube was more often higher 

 near the mouthpiece than when the quantity of expired air was 

 less. The fact demonstrated in these Tables, that the more air 

 expelled from the lungs, the greater was the tendency for the 

 percentage of carbon dioxide to increase continuously as the air 

 left the mouth, suggested that the time occupied in breathing out 

 the air affected the result. Experiments, therefore, were carried 

 out in which the air was expelled slowly during several seconds, 

 and others during which the air was expelled more rapidly. Two 

 seconds represent the minimal time in which the subject could 

 expel two litres of air. The experiments in which the air was 

 expired less quickly may be recorded first. In these experiments, 

 the conditions were exactly similar to those of the experiments 

 recorded in Table vi. The results appear in Table vii. 



These results show that, when the air leases the lungs during 

 several seconds, the alveolar expired air contains more carbon 

 dioxide the longer the expiration continues. The successive 

 portions of the expired air thus show an increased concentration 

 of carbon dioxide, the later they leave the air-passages. 



