THE VARIATIONS DURING LIFE 



119 



observed regular diurnal variations in the resting metabolism of a man 

 fasting for 31 days. 



Lindhard [1910, 1912] has observed very pronounced seasonal 

 variations. He made determinations of the carbon dioxide output in 

 half-hour periods on himself during an arctic expedition (North-East 

 Greenland, 76 46' N. Lat.). The experiments were made under ap- 

 proximately standard conditions each morning fasting and in a kneeling 

 position. 1 Consecutive series of about ten experiments were made 

 and such series repeated every 2 to 3 months. The agreement of the 

 experiments in each series is remarkable. Lindhard found that during 

 the arctic summer day, which lasts in that latitude from the end of 

 April until September, the standard metabolism is increased as com- 

 pared with the winter night. 



TABLE XXVIII. 



Along with the increase in metabolism an increase in pulmonary 

 ventilation and a decrease in alveolar CO 2 tension were also observed. 

 The increase in ventilation will account for part of the increase in 

 metabolism through the increased work of the respiratory muscles (see 

 p. 59), but the general effect is ascribed by Lindhard to the light 

 acting indirectly as a climatic factor. ' Similar but much less pro- 

 nounced variations were observed by Lindhard in a series of experiments 

 made in Copenhagen upon two other subj'ects. The difference in light 

 between summer and winter is of course much less at 56 northern 

 latitude than at 76. 



2. The influence of muscular training. It has been shown by 

 Zuntz and Schumburg [1901] for man and by Zuntz [1903] for the dog 

 that the standard metabolism is increased after a prolonged period of 

 severe muscular work. This increase may be due partly to an in- 

 crease in the amount of muscular tissue, but in some cases at least an 



1 The space available in the laboratory did not allow any other. 



2 Muscular training was probably to a pertain extent responsible for the high figure for 

 November, See below. 



