Il8 RESPIRATION 



when the consumption of oxygen and accumulation of carbon dioxide 

 and other matters interfere more or less with the respiratory function. 

 As employed by Regnault and Reiset, it is adapted only to experiments 

 on animals of small size. These give an approximate idea, however, of 

 the processes as they take place in the human subject. Pettenkofer 

 constructed a chamber large enough to admit a man and allow freedom 

 of motion, eating, sleeping etc., into which air could be introduced in 

 definite quantity, and from which the products of respiration were 

 removed and estimated. This method had been adapted to the human 

 subject on a small scale in 1843, by Scharling; but there was no arrange- 

 ment for estimating the quantity of oxygen consumed. 



Estimates of the quantities of oxygen consumed or of carbon dioxide 

 exhaled, based on analyses of the inspired and expired air, calculations 

 from the average quantity of air changed with each respiratory act and 

 the average number of respirations per minute, are not so reliable as 

 analyses showing the actual changes in the air, like those of Regnault 

 and Reiset. Where there is so much multiplication and calculation, a 

 slight inaccuracy in the estimates of the quantities consumed or pro- 

 duced in a single respiration will make a large error in the estimate for 

 a day or even for an hour. Bearing in mind these sources of error, from 

 the experiments of Valentin and Brunner, Dumas, Regnault and Reiset 

 and others, a sufficiently accurate approximation of the proportion of 

 oxygen consumed by the human subject may be made. The air, which 

 contains, when inspired, about twenty-one per cent of oxygen, is found 

 on expiration to contain but about sixteen per cent. In other words, 

 the volume of oxygen absorbed in the lungs is about five per cent of 

 the volume of air inspired. 



The quantity of oxygen consumed in respiration is subject to great 

 variations, depending on temperature, the condition of the digestive sys- 

 tem, muscular activity etc. The following conclusions, the results of the 

 observations of Lavoisier and Seguin, give at a glance the variations 

 from the above-mentioned causes : 



"I. A man, in repose and fasting, with an external temperature of 

 about 90 Fahr. (32.5 C.), consumes 1465 cubic inches (24 liters) of 

 oxygen per hour. 



" 2. The same man, in repose and fasting, with an external tempera- 

 ture of 59 Fahr. (15 C.), consumes 1627 cubic inches (26.66 liters) of 

 oxygen per hour. 



" 3. The same man, during digestion, consumes 2300 cubic inches 

 (37.69 liters) of oxygen per hour. 



"4. The same man, fasting, accomplishing the labor necessary to 

 raise, in fifteen minutes, a weight of about 16 pounds 3 ounces (7-343 



