APPENDIX II. 169 



every other part of the body, requiring a continuous 

 change of substance, whilst the chief function of the 

 non-nitrogenous is to furnish by their oxidation the 

 actual energy which is in part transmuted into mus- 

 cular force. 



The combustible food and oxygen coexist in the 

 blood which courses through the muscle, but when 

 the muscle is at rest there is no chemical action 

 between them. A command is sent from the brain 

 to the muscle ; the nervous agent determines oxida- 

 tion. The potential energy becomes active energy, 

 one portion assuming the form of motion, another 

 appearing as heat. Sere is tlie source of animal 7ieat } 

 here the origin of muscular power ! Like the piston 

 and cylinder of a steam-engine, the muscle itself is 

 only a machine for the transformation of heat into 

 motion ; both are subject to wear and tear and 

 require renewal, but neither contributes in any 

 important degree by its own oxidation to the actual 

 production of the mechanical power which it exerts. 



lOthly. From this point of view it is interesting to 

 examine the various articles of food in common use, 

 as to their capabilities for the production of muscu- 

 lar power. The speaker had therefore made careful 

 estimations of the calorific value of different ma- 

 terials used as food, by the same apparatus and in 

 the same manner as described above for the determi- 

 nation of the actual energy in muscle, urea, uric 

 acid, and hippuric acid. 



The results are embodied in the following series 

 of tables, but it must be borne in mind that it is 

 only on the condition that the food is digested and 



