/ XILUENCE OF TIME OF DA V. 
721 
The influence of time of day upon the respiratory exchange. — 
During a series of experiments performed in the years 1813 and 1814, 
Prout l 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 Yierordt, 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 folio wing- 
curve represents the daily variation observed by Fredericq in the oxygen 
absorbed bv a man : — 
A. M. 
P m. 
8 © 10 11 12 1 
2 3 « 5 © 7 
f 
6 
5 
• 
/\ 
• 

\ 
< 
• f 
^ 
• 
• 
^ 
• 
• 
•X. 
v 
« x 
^R 
• 
■^ 
' R 
•V 
• 
*^ 
Fig. 67. 
-Fredericq's curve of daily variation in the absorption of oxygen. 
R = time of a meal. 
The cau,-e.^ 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 Pettenkofer and Yoit, 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. 
2 "Physiol, d. Athrnens," Karlsruhe, 1815; "\Vagner"s "Handworterbuch," Bd. ii. 
S. 883. 
3 " Untersuch. ueber Sauerstoffserbrauch u. Kohlensaureausathmung des Menschen," 
Cassel, 1871, S. 31 : Arch./, exper. Path. u. Pharmakol., Leipzig, 1874, Bd. ii. S. 105 ; 
ibid., 1880, Bd. xii. S. 1. 
4 " Einfiuss der Athembewegungen auf die Ausscheidung der Kohlensiiure durch die 
Lungen," Dorpat, 1869. 
5 Arch, ili- bioJ., Gand, 1SS2, tome iii. p. 729. 
rt Phil. Trans., London, 1859, voL.cxlix. p. 681. 
7 Ztschr.f. Biol., Miinchen, 1866, Bd. ii. S. 459. 
- Saint-Martin, Compt. rend. Acad. d. sc, Paris, 1887, tome cv. p. 1124 ; Rubner, 
Bcitr. z. Physiol. Carl Ludw'nj z. s. 70 Geburtst., Leipzig, 1887, S. 259. 
VOL. I. — 46 
