108 Dr. W. Marcet. On the Chemical [Jan. 15, 



barely from 1 to 2 mm. of difference of pressure, which is inappre- 

 ciable. 



Placing the nose-piece in his nostrils, the operator breathes through 

 his month for a few seconds, then he takes the mouth-piece in his 

 mouth, and inhales the air of the bell-jar through the nose-piece, the 

 bell -jar falling ; at that very instant the chronograph is started. The 

 next expiration is from the month through the U-tube into the bell- 

 jar, and so on, the air re-breathed circulating through the bell-jar. 

 After five minutes have elapsed, every attention is given to stop the 

 inspiratory tube and arrest the chronograph at the very end of an 

 expiration, while another assistant opens the double-way cock, con- 

 nected through tubing with the operator, and disposed so as to lead 

 the air now expired into the other bell-jar ; the operator drops the 

 nose-piece and takes an inspiration of fresh air, through the nose, then 

 he expires out of the mouth into the empty bell- jar. He was, perhaps, 

 beginning to feel a little uncomfortable ; sometimes a slight sensation 

 of want of air was experienced, but not always, and one of my subjects 

 hardly noticed any effect. I think I was affected most of the four 

 who submitted to experiment, although it repeatedly happened that I 

 felt no discomfort of any kind, beyond perhaps a slight want of air. 



Fresh air is inhaled with an undoubted sensation of comfort, and 

 the volume of this air is in marked excess of the volume inhaled in 

 ordinary breathing. During the first two or three minutes, large 

 volumes of fresh air are inspired, then the breathing quickly subsides, 

 and before 36 or 37 litres have been expired it has apparently resumed 

 its usual rate, with the disappearance of all feeling of discomfort. 



I have stated above that the air re-breathed had been transferred 

 from the bell-jar into an india-rubber bag, allowing the bell- jar to be 

 utilised for collecting the air expired in the last stage of the experi- 

 ment. The india-rubber tube and double- way cock were so arranged 

 that by turning the cock the operator was placed in connexion with 

 the empty bell-jar, and during an inspiration of fresh air the cock 

 was turned, when the expired air was directed into that bell-jar. 



The rate of breathing had now become all but natural, or the 

 same as at the beginning of the experiment, giving indications 

 the effects of re-breathing had apparently passed away ; this question 

 was to be settled by the analyses. 



There were consequently four different samples of expired air to be 

 submitted to analysis for the determination of the carbonic acid they 

 contained. The first sample was frbm air expired normally, the 

 second from air re-breathed, the third from air expired immediately 

 after re-breathing, the fourth from air expired after apparent recovery 

 from the effects of breathing impure air. 



By the time breathing in the closed vessel had commenced, the air 

 expired normally had already been shaken with barium hydrate; 



