788 CHANGE OF COMPOSITION OF ALVROLAR AIR, 



Leimdorfer (1909) determined the composition of alveolar air 

 after inspirations of ordinary air, and of gaseous mixtures con- 

 taining different percentages of carbon dioxide and oxygen, had 

 been held in the lungs as long as possible. He, too, found that 

 excess of oxygen raised the final percentage of carbon dioxide 

 attained, and concluded that the time for which the breath could 

 be held was determined by the percentage of oxygen in the 

 alveolar air. 



Du Bois-Reymond (1910) connected one lobe of the lung of 

 an animal with a space filled with nitrogen, and observed the 

 I'ate at which carbon dioxide was given off into this space. He 

 found that the percentage of carbon dioxide rose at a logarith- 

 mically decreasing rate, and approached a certain final value. 



Christiansen, Douglas, and Haldane (1914) carried out ex- 

 periments to determine the composition of alveolar air after 

 holding in the lungs mixtures of air containing various percent- 

 ages of carbon dioxide. The lungs, in fact, were used as an 

 a«rotonometer. When the percentage of carbon dioxide in the 

 inspired mixture was below a certain value, the percentage in 

 the alveolar air was greater after holding the breath than that 

 present in the original mixture. When, however, the percentage 

 of carbon dioxide in the mixture was greater than this value, 

 the alveolar percentage, after holding the breath, was less than 

 that in the original mixture; that is, carbon dioxide had been 

 absorbed by the blood. These investigators concluded that the 

 percentage of carbon dioxide in the inspired air above which 

 carbon dioxide was absorbed by the blood, and below which 

 carbon dioxide was given off by the blood, was the percentage 

 in the alveolar air with which the venous blood was in equi- 

 librium in the lungs, and from which the venous tension of 

 carbon dioxide in the lungs could be calculated. These workers 

 also measured the percentages of carbon dioxide in the alveolar 

 air after holding the breath for various periods. They found 

 that the alveolar percentage of carbon dioxide continued to rise 

 during the whole period for which the breath was held, and con- 

 cluded that the venous tension of carbon dioxide could not be 

 determined by observations of this kind. 



