480 THE HUMAN BODY. 



The Energy Lost by the Body in Twenty-four Hours 



Practically speaking, the Body only loses energy in two 

 forms; as heat and mechanical work: by applying conduct- 

 ors to different parts of its surface small amounts of elec- 

 tricity can be carried off, but the amount is quite trivial in 

 comparison with the total daily energy expenditure. During 

 complete rest, that is, when no more work is done than that 

 necessary for the maintenance of life, nearly all the loss takes 

 the form of heat. The absolute amount of this will vary 

 with the surrounding temperature and other conditions, but 

 on an average a man loses, during a day of rest, 2700 calories; 

 that is enough to raise 2700 kilograms (5940 Ibs.) of water 

 from to 1 C. (from 32 to 33 8 F.); otherwise expressed, 

 this amount of heat would boil 27 kilos (59.4 Ibs.) of ice-cold 

 water. This does not quite represent all the energy lost by 

 the Body in that time: since a small proportion is lost aa 

 mechanical work in moving the clothes and air by the respir- 

 atory movements, and even by the beat of the heart, which <it 

 each systole pushes out the chest-wall a little and moves the 

 things in contact with it. The working Body liberates and 

 loses much more energy; part as mechanical work done on 

 external objects, part as increased heat radiated or conducted 

 from the surface, or carried off by the expired air in. the 

 quickened respirations. Every one knows that he feels 

 warmer when he takes exercise, and this is due to the greater 

 amount of blood then carried to the skin and raising for the 

 time its temperature. The general temperature of the Body 

 as measured in the mouth is not at all or only very slightly 

 raised, however, as the greater loss of heat from the skin keeps 

 the average temperature of the blood at its normal level. This 

 greater loss corresponding to the greater production has been 

 measured on persons enclosed in specially constructed calori- 

 meters; and though there are considerable difficulties in the 

 way of getting quite accurate results, the measurements show 

 that the heat produced and lost in a day of moderate work is 

 about one third greater than that in a day of rest. The fol- 

 lowing table gives more definite numbers: 



Day of Rest. Day of Work. 



Rest 16 hrs. Sleep 8 hrs. Rest 8 hrs. Work 8 hrs. Sleep 8 hrs. 

 Heat-units (calo- ) 

 ries) produced \ 24~QA 320 1235.2 2169.6 320. 



10,885 Fah.-lb. \ ,,, R / 14,528 Fah.-lb. 



heat-units. ) 3724.8 ( | ie at-units. 



