112 VETEKINAEY HYGIENE 



amount of energy necessary to raise the temperature of one 

 pound of water 1° Fahr., is equivalent to raising one pound 

 772 feet high. 



The mechanical equivalent of 1° Fahr. is, therefore, 772 

 foot pounds. 



With this data the potential energy, or mechanical value, 

 of the proximate principles of food can be calculated. 



1 oz. proteid oxidised in the body yields 170 foot tons of energy. 

 1 oz. fat „ „ „ 380 ,, ,, 



1 oz. starch „ „ ,, 138 ,, ,, 



1 oz. sugar „ ,, „ 130 „ „ 



1 oz. carbon converted into COj „ 311 ,, ,, 



But the total energy which food is capable of yielding is 

 not converted into work ; the muscles of the body compared 

 with an ordinary machine are most economical in their 

 working, but in spite of this in man not more than one- 

 fifth of the theoretical energy of the food appears as work, 

 and recent investigations have placed it even lower. 



The muscles of the horse would in this respect appear to 

 be somewhat better engines than human muscles, as both 

 Wolff and Lehmann found that about 81'5 per cent, of the 

 digestible substances in food appeared as work. 



The combustion of proteid, fat, and carbo-hydrates in 

 the body has been likened to the combustion of fuel in an 

 engine, viz., that a conversion of heat into force occurs. 



Calculations have caused physiologists to believe that 

 twenty to thirty per cent, of the heat in the food was 

 converted into work; but Wolff takes up a new attitude 

 and objects, with a good show of reason, to the source of 

 muscular power residing in the combustion of the food. 

 He says that an engine and the animal body are not 

 comparable. 'If a simple conversion of heat into work 

 really takes place in the body, then the increased oxidation 

 of organic matter which takes place during work, must 

 result in a continual and renewed source of muscular 

 power, and render external work possible without any 

 cessation.' 



The theory he brings forward is that the food substances 



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