140 CHANGES OF AIR AND BLOOD IN RESPIRATION. 



adult male, during repose and in normal conditions of health and tem- 

 perature." 



In passing through the lungs, the air, in addition to losing a certain pro- 

 portion of its oxygen, undergoes the following changes : 



1. Elevation in temperature. 



2. Gain of carbon dioxide. 



3. Gain of watery vapor. 



4. Gain of ammonia. 



5. Gain of a small quantity of organic matter. 



6. Gain, and occasionally loss, of nitrogen. 



The elevation in temperature of the air which has passed through the 

 lungs has been studied by Grehant. He found that with an external tem- 

 perature of 72 Fahr. (22-22 C.), respiring seventeen times per minute, the 

 air taken in by the nares, and expired by the mouth through an apparatus 

 containing a thermometer carefully protected from external influences, marked 

 a temperature of 95-4 Fahr. (35'22 C.). Taking in the air by the mouth, 

 the temperature of the expired air was 93 Fahr. (33'89 C.). At the begin- 

 ning of the expiration, Grehant noted a temperature of 94 Fahr. (34'44 C.). 

 After a prolonged expiration, the temperature 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 the variations in the quan- 

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

 the great influence of the rapidity of the respiratory movements, it is difficult 

 to fix upon any number that will represent the average proportion of this gas 

 contained in the expired air. The same influences were found affecting the 

 consumption of oxygen, and the same difficulties were experienced in form- 

 ing an estimate of the proportion of this gas consumed. As it was 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 approximation, that in the intervals of digestion, 

 in repose and under normal conditions 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 which 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 ex- 

 haled. 



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

 expired air, depending upon 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 upon 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 respira- 

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



