430 RESPIRATION. 



weight. Breakfast was taken at 8J A.M., dinner at 1J, tea at 

 5, and supper at 8 P.M. The observations occupied ten min- 

 utes, and were made every hour and half-hour for 18 hours. 

 The average for the 18 hours gave 20,082 cubic inches of 

 carbonic acid for the whole period. Observations during the 

 6 hours of sleep showed a total exhalation of 4,126 cubic 

 inches. This, added to the quantity exhaled during the day, 

 gives as the total exhalation in the twenty -four hours, during 

 complete repose, 24,208 cubic inches (about 13 '45 cubic feet), 

 containing 7*144 oz. av. of carbon. 1 



Considering the great variations in the exhalation of car- 

 bonic acid, this estimate can be nothing more than an ap- 

 proximation. One of the great modifying influences is mus- 

 cular exertion, by which the production of carbonic acid is 

 largely increased. This would indicate a larger quantity 

 during ordinary conditions of exercise, and a much larger 

 quantity in the laboring classes. Dr. Smith gives the fol- 

 lowing approximate estimates of these differences : 2 



In quietude 7*144 oz. av. of carbon. 



Xon-laborious class 8'68 " " 



Laborious class 11*7 " " 



In studying the variations in the exhalation of carbonic 

 acid, important information has been derived from experi- 

 ments by many observers on the inferior animals, as well as 

 from the observations of Dumas, Prout, Scharling, and others 

 on the human subject. The principal conditions which 

 influence the exhalation of this principle are : 



Age and sex ; activity or repose of the digestive system ; 

 form of diet ; sleep ; muscular activity ; fatigue ; moisture, 

 and surrounding temperature ; season of the year. 



1 Op. cit., p. 692. In these calculations there is a slight arithmetical error ; 

 but it makes a difference of only 40 cubic inches of gas in the estimate for the 24 

 hours. In the original paper, the quantity is given by weight. We have re- 

 duced it to cubic inches, assuming that 100 cubic inches of gas weigh 47'26 grains. 



8 Op. dt., p. 693. 



