THE HEAT OF THE BODY. 481 



The mechanical work done on the working day represented 

 in addition an expenditure of energy of 213,344 kilogram- 

 meters, which is equal to 502 calories. Of the excess heat in 

 the working day, part is directly produced by the increased 

 chemical changes in the quicker working heart and respira- 

 tory muscles, and the other muscles set at work; while part 

 is indirectly due to heat arising from increased friction in the 

 blood-vessels as the blood is driven faster around them, and 

 to friction of the various muscles used. The average cardiac 

 work in twenty-four hours is about 60,000 kilogrammeters; 

 that of the respiratory muscles about 14,000; and since nearly 

 all of both is turned finally into heat within the Body, we 

 have 74,000 kilogrammeters of energy answering to about 174 

 calories (6786 Fah.-lb. units) indirectly produced in the rest- 

 ing Body daily from these sources. 



Of 100 parts of heat lost from the resting Body, about 

 74.7 are carried off in radiation or conduction from the skin. 

 14.5 are carried off in evaporation from the skin. 

 5.4 " " " " " " lungs. 



3.6 " " " . expired air. 

 1.8 " " the excretions. 



In a day of average work, of every 100 parts of energy lost 

 in any form from the Body 

 1-2 go as heat in the excreta. 

 3-4 iii heating the expired air. 



20-30 in evaporating water from the lungs and skin. 

 60-75 in heat radiated or conducted from the surfaces and in 

 external mechanical work. 



It is obvious, however, that such numbers are only rough 

 approximations and must vary greatly with the temperature 

 and moisture of the surrounding air, the rate of respiration, 

 and other circumstances. 



The Superiority of the Body as a Working Machine. 

 During eight hours of work we find (see table) the Body 

 loses 2169.6 calories of energy as heat, and can do simul- 

 taneously work equivalent to 502 calories. So of all the 

 energy lost from it in that time about \ may take the form of 

 mechanical work; this is a very large proportion of the total 

 energy expended, being a much higher percentage than that 

 given by ordinary machines. The best steam-engines can 

 utilize as mechanical work only about | of the total energy 

 liberated in them and lost from them :n a given time, the 



