4 i2 TEXT-BOOK OF PHYSIOLOGY. 



THE TOTAL RESPIRATORY EXCHANGE. 



The total quantities of oxygen absorbed and carbon dioxid discharged 

 by a human being in twenty-four hours are measures of the intensity of the 

 respiratory process, and an indication of the extent and character of the 

 chemic changes attending all life phenomena. Their determination and 

 their relation to each other are matters of interest and importance. The 

 quantities which have been obtained by different observers are the outcome 

 of calculations based on certain groups of data and of experiments made with 

 special forms of apparatus. 



Thus from the total air breathed daily, estimated from the amounts 

 obtained during a longer or shorter period by experiments with spirometric 

 apparatus, and from the percentage loss of oxygen and gain of carbon dioxid 

 shown by an analysis of the respired air, it can be calculated at least ap- 

 proximately what the total amounts of oxygen absorbed and carbon dioxid 

 exhaled must be. If it be assumed that the minimum daily volume of air 

 breathed is 8500 liters and the maximum volume 12,752 liters, and the 

 percentage loss of oxygen is 4.78, then the total volume of oxygen absorbed 

 is 406 liters (580 grams) or 609 liters (870 grams). By the same method the 

 total carbon dioxid exhaled daily is found to be either 372 liters (735 grams) 

 or 558 liters (1103 grams). The direct experiments which have been made 

 with specially devised forms of apparatus, both on human beings and animals, 

 have yielded similar results. With those forms which are adapted for both 

 human beings and animals Scharling's, Pettenkofer and Voit's it is only 

 possible, however, to determine the amount of carbon dioxid and water exhaled 

 and from them to calculate the amount of oxygen absorbed. This is done by 

 deducting the loss in weight by the man or animal during the experiment 

 from the combined weights of the carbon dioxid and water discharged. 

 The difference represents the oxygen absorbed. 



The Pettenkofer- Voit apparatus consists essentially of a chamber large 

 enough to admit a man and capable of being made air-tight with the 

 exception of an inlet for air for breathing purposes. The respired air is 

 drawn through a tube and measured by a large meter turned by a water or 

 gas motor. By means of a side tube a fractional quantity of the main 

 column of air is diverted to an absorption apparatus by a small pump. 

 This air first passes into a vessel containing H 2 SO 4 , by which the water is 

 collected; then into long tubes containing barium hydroxid, by which the 

 carbon dioxid is absorbed; thence into a small meter, by which its amount is 

 registered. From the amount of water and carbon dioxid thus obtained 

 the amounts of both in the total air breathed are calculated. The water and 

 carbon dioxid previously present in the air are simultaneously determined by 

 a corresponding absorption apparatus and deducted from the amounts ob- 

 tained from the respired air. As the apparatus is traversed constantly by a 

 column of air of normal composition and the waste products removed as rapidly 

 as discharged, the experiment can be continued for periods varying from 

 six to twenty-four hours without detriment to the subject of the experiment. 



With those forms adapted only for animals Regnault's and Reiset's, or 

 Jolyet and Regnard's it is possible to determine simultaneously the ab- 

 sorption of oxygen and the discharge of carbon dioxid. As the apparatus 



