EXHALATION OF CARBON DIOXIDE 121 



perature was 96 Fahr. (35.55 C). In these observations the temperature 

 taken beneath the tongue was 98 Fahr. (36.67 C.). 



Exhalation of Carbon Dioxide. On account of variations in the quan- 

 tities of carbon dioxide exhaled at different times of the day, and par- 

 ticularly the influence of the rapidity of the respiratory movements, it is 

 difficult to fix on any number that will represent the average proportion 

 of this gas contained in the expired air. The same influences have been 

 found affecting the consumption of oxygen, and the same difficulties are 

 experienced in forming an estimate of the proportion of this gas con- 

 sumed. As it may be assumed, after a comparison of the results obtained 

 by different observers, that the volume of oxygen consumed is about five 

 per cent of the entire volume of air, it may be stated, as an approxima- 

 tion, that in the intervals of digestion, in repose and under normal condi- 

 tions as regards the frequency of the pulse and respiration, the volume 

 of carbon dioxide exhaled is about four per cent of the volume of the 

 expired air. As the volume of oxygen that enters into the composition 

 of a definite quantity of carbon dioxide is equal to the volume of the 

 carbon dioxide, it is seen that a certain quantity of oxygen disappears in 

 respiration and is not represented in the carbon dioxide exhaled. 



There are great differences in the proportion of carbon dioxide in the 

 expired air, depending on the time during which the air has remained in 

 the lungs. This point was studied by Vierordt, in a series of ninety-four 

 experiments made on his own person, with the following results : 



" When the respirations are frequent, the quantity of carbon dioxide 

 expelled at each expiration is much less than in a slow expiration ; but 

 the quantity of carbon dioxide produced during a given time by frequent 

 respirations is greater than that which is thrown off by slow expirations." 



The air that escapes during the first part of an expiration is less rich 

 in carbon dioxide than that which is last expelled and comes directly 

 from the deeper portions of the lungs. Dividing, as nearly as possible, 

 the expiration into two equal parts, Vierordt found, as the mean of 

 twenty-one experiments, a percentage of 3.72 in the first part of the 

 expiration and 5.44 in the second part. 



Temporary arrest of respiratory movements has a marked influence 

 in increasing the proportion of carbon dioxide in the expired air, although 

 the absolute quantity exhaled in a given time is diminished. In a number 

 of experiments on his own person, Vierordt ascertained that the per- 

 centage of carbon dioxide becomes uniform in all parts of the respiratory 

 organs after holding the breath for forty seconds. Holding the breath 

 after an ordinary inspiration, for twenty seconds, the percentage of car- 

 bon dioxide in the expired air was increased by 1.73 per cent above the 

 normal standard ; but the absolute quantity exhaled was diminished by 



