Scientific Lectures. 241 



leaving it ; and since oxydation always evolves lieat, the lieat of the 

 body must have its origin in tlie oxydation of the food. Moreover, 

 careful measurements have demonstrated that the amount of heat 

 given otf by the body of a man weighing ISO pounds, is about 

 2,500,000 units. Accurate calculations have shown, on the other 

 hand, that 2S8*4 grams of carbon and 12*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.* 

 We conceive, however, that no long argument is necessary to prove 

 that animal heat results from a conversion of energy witliin t]ie])ody, 

 or that the vital force heat is as truly correlated to the other forces as 

 when it has a purely physical origin. 



The belief that the muscular force exerted by an animal 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. Frankland 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 locomotive drive a train with 

 out fuel.'' t In studying the characters of muscular action we 

 notice, first, that, as in the case of heat, the force which it 

 develops is in nowise diflerent from motion in inorganic nature. 

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

 traction of muscle, was used to show the conversion of mass force 

 into molecular force. No one in tliis room believes, I presume, that 

 the result would have been at all difierent, had the motion been 

 supplied by a steam engine or a water wheel. Again, food, as we 

 have seen, is of value for the potential energy it contains, which may 

 become actual in the body. Liebig, in 1842, asserted that for the 

 production of muscular force, the food must first be converted into 

 muscular tissue,;]: a view until recently accepted by physiologists. § 

 It has been conclusively shown, however, witliin a few years, that 



♦M&rehall, John, Outlines of Phypiology, American edition, 1868, p. Olfi. 



+ Frankland, Edward, On tlie Source of Muscular Power, Proc. Hoy. Inst., June 8, ISGG; Am. J. 

 Sci., II. xlii, 393, Nov. 1866. 



i Liebig, Justus von, Die organische Chemie in ihrnr Anwondun? fluf Physinlogio nnd Pathologic, 

 Braunschweig, 18«. Also in his Animal Chemistry, edition of ISnS (Am. cd., p. 26), where ho aays 

 "Every motion increases the amount of organized tissue which undergoes metamorphosis." 



§ Compare Draper, John Wm., Human Physiology. Playfair, Lyon, On the Food of ilau in relation 

 to his useful work ; Edinburgh, 186.5; Proc. Koy. Inst., April 28, 1805. Ranke, Tetanus einc Physio- 

 logische Studio ; Leipiig, 1865. Odling, op. cU. 



[IXST.] 16 



