252 



Metabolism of Healthy Max. 



insisted upon in all cases. In recent investigations with more sensitive calo- 

 rimeters which permit of experimental periods as short as one hour, it has been 

 found that the human body gives wonderfully accurate results when used for 

 experimenting. With the same muscular activity and the same preceding diet, 

 the metabolism can be predicted with almost unerring accuracy. Until a large 

 number of other experiments have been made in which the energy transforma- 

 tion and katabolism involved in the ordinary household routine of everyday life 

 have been more completely studied, we can not compute the daily requirement of 

 man on a very accurate basis, yet the experiments here reported enable us to 

 form some general opinion of the variations in the energy transformations 

 during the day. 



Assuming the energy transformation when a man is sitting quietly at rest 

 (the condition obtaining in the large majority of our experiments) in a chair 

 as 100, we can compute the relative variations above or below this point with 

 either decreased or increased muscular activity. Thus, during sleep the mus- 

 cular activity is very much decreased, and the total katabolism is less. In 

 standing, the katabolism is somewhat greater than in sitting. On this basis, 

 the relative values for a number of the various muscular activities have been 



Table 106. Percentage variations in the average output of carbon 



dioxide and heat and intake of oxygen under different 



conditions of activity as compared ivith sitting. 



[Sitting = 100.] 



computed and presented in table 106. It is very difficult to express what is 

 meant by the various terms light muscular work, moderate muscular work, 

 severe muscular work, and very severe muscular work and hence no attempt 

 is made here to define them. The very severe muscular work is included simply 

 to show the energy transformation when a man is working at nearly the limit 

 of his strength and endurance. Unfortunately one of the most highly desired 

 factors in ordinary life is missing in this case, namely, the energy transforma- 

 tion during walking. With a calorimeter that is now being designed and 

 shortly to be built at the Nutrition Laboratory, the problem of the motion of 

 forward progression and energy transformation attendant tbereon will be 

 given a special consideration. Until this apparatus is perfected and tested, the 

 only information we have that is in any way satisfactory are the observations of 

 Zuntz in which a portable gas-meter was used. These observations signify that 

 there is an hourly expenditure of about 160 calories over and above the resting 

 maintenance requirement by a man of 70 kilos walking along a level road at a 



