INFLUENCE OF TIME OF DAY. 



721 



The influence of time of day upon the respiratory exchange. 

 During a series of experiments performed in the years 1813 and 1814, 

 Prout 1 discovered that the amount of carbon dioxide discharged from 

 the lungs appeared to be influenced by the time of day, for there was a 

 regular daily variation; the maximum was generally between 11 A.M. 

 and 1 P.M. ; then there was a fall to the minimum at 8 P.M. or 9 P.M. in 

 the evening, and at this low level the discharge of carbon dioxide 

 remained until 3 A.M. or 4 A.M., when there was a marked rise. A 

 similar variation was observed by Vierordt, 2 both in the discharge of 

 carbon dioxide and in the amount of air respired, and the cause of the 

 rise he attributed to food. The table on p. 722 gives his average results. 



Speck 3 determined the daily variation, both in the intake of oxygen 

 and in the output of carbon dioxide, and showed the influence of food in 

 producing the maximum. 



Further experiments upon the daily variation in the respiratory 

 exchange have been made by Berg 4 and Fredericq. 5 The following 

 curve represents the daily variation observed by Fredericq in the oxygen 

 absorbed by a man : 



A. M. 



P.M. 



8 9 10 11 12 1 2 34 3 67 



4.5 



\ 



\ 



\ 



FIG. 67. Frederick's curve of daily variation in the absorption of oxygen. 

 R = time of a meal. 



The causes of these variations in the daily respiratory exchange are 

 to be attributed mainly to food and muscular activity, for during sleep, 

 as E. Smith, 6 Pettenkof er and Voit, 7 and others 8 have shown, the meta- 

 bolism is greatly diminished, and also in a less degree during hunger. 

 In addition, however, there appears to be a certain periodicity stamped 



1 Ann. Phil., London, 1813, vol. ii. p. 330 ; vol. iv. p. 331. 



3 "Physiol. cl. Athmens." Karlsruhe, 1845: Wagner's "Handworterlmch," Bd. ii. 

 S. 883. 



3 "Untersuch. ueber Sauerstoffserbrauch u. Kolilensaureausathmung des Menschen," 

 Cassel, 1871, S. 31 ; Arch. f. exper. Path. u. PharmakoL, Leipzig, 1874, Bd. ii. S. 405 ; 

 ibid. 188Q, Bd. xii.'S. 1. * 



" Einfluss der Athembewegungen auf die Aitsscheidung der Kohlensaure durch die 

 Lungen," Dorpat, 1869. 



5 Arch, de bidl., Gand, 1882, tome iii. p. 729. 



fi Phil. Trans., London, 1859, vol. cxlix. p. 681. 



1 Ztschr.f. Biol., Miinchen, 1866, Bd. ii. S. 459. 



8 Saint-Martin, Compt. rend. Acad. d. sc., Paris, 1887, tome cv. p. 1124; Rubner, 

 Beitr. %. Physiol. Carl Ludwiy 3. s. 70 Geburtst., Leipzig, 1887, S. 259. 

 VOL. I. 46 



