THK MAINTENANCE OF THE ANIMAL HEAT. 383 



suits of such experiments would, of course, vary largely ac- 

 cording to the nature of the person experimented upon. In 

 a person resting, about 2,500,000 calories are liberated in 

 one day ; or, measuring that in terms of the water which it 

 would heat, it would be an amount of heat sufficient to raise 

 56 pounds of ice water to the boiling point. These figures 

 are materially increased for a day of regular work. In a 

 working day no less than 3,700,000 calories are produced. 

 This amount of heat would be sufficient to raise 83 pounds 

 of water from the freezing to the boiling point. 



These figures appear at first startling and it seems almost 

 incredible that in one day, losses so large should occur. 

 However, the fact that this heat is being continually radi- 

 ated little by little explains this popular error. It is further 

 interesting to know that the amount of heat lost by the en- 

 tire body, plus the amount of energy lost in muscular motion, 

 is about the same as the food taken during the day would 

 give if directly oxidized outside of the body. This agree- 

 ment between the theoretical amount of heat in the foods 

 taken and the actual amount of heat lost in the body when 

 that body is in a state of nutritive equilibrium proves with- 

 out further question the source of all the energy of the body 

 and the absurdity of calling in any so-called vital force to 

 explain an apparent discrepancy. 



The interesting question at once follows, in what man- 

 ner this large amount of heat is daily lost from the body. 

 Here, too, fairly accurate experiments help us out and show 

 about the following distribution of the loss: 



73 per cent, direct radiation from the skin; 



i4*/2 " evaporation of the perspiration from the skin; 



7 2 Ao from the lungs; 



3 5 /io " in the warmth of the expired air; 



i 8 /io " lost in warming the excretions of the body. 



It was pointed out in a previous chapter that of the 

 available energy of the body about five-sixths is lost in heat, 

 and only one-sixth utilized in actual muscular movements. 

 This seems a very heavy proportion of loss of heat, and yet 



