(i7) 53 



this may be added the chemical argument that while 

 food capable of yielding heat by combustion is taken 

 into the body, its constituents are completely or almost 

 completely, oxidized before leaving it ; and since oxida- 

 tion always evolves heat, the heat of the body must 

 have its origin in the oxidation of the food. Moreover, 

 careful measurements have demonstrated that the amount 

 of heat given off by the body of a man weighing 180 

 pounds is about 2,500,000 units. Accurate calculations 

 have shown, on the other hand, that 288*4 grams of car- 

 bon and 1 2 '56 grams of hydrogen are available in the 

 daily food for the production of heat. If burned out of 

 the body, these quantities of carbon and hydrogen would 

 yield 2,765,134 heat units. Burned within it, as we have 

 just seen, 2,500,000 units appear as heat ; the rest in 

 other forms of energy. 21 We conceive, however, that no 

 long argument is necessary to prove that animal heat 

 results from a conversion of energy within the body j or 

 that the vital force heat, is as truly correlated to the 

 other forces as when it it has a purely physical origin. 



The belief that the muscular force exerted by an ani- 

 mal is created by him is by no means confined to the 

 very earliest ages of history. Traces of it appear to 

 the careful observer even now, although, as Dr. Frank- 

 land says, science has proved that "an animal can no 

 more generate an amount of force capable of moving a 

 grain of sand than a stone can fall upward or a loco- 

 motive drive a train without fuel." 22 In studying the 

 characters of muscular action we notice, first, that, as 

 in the case of heat, the force which it develops is in no 

 wise different from motion in inorganic nature. In the 

 early part of the lecture, motion produced by the con- 



