194 Prof. Frankland on the Origin of Muscular Power. 



starch, fat, &c, are the chief sources of the actual energy which 

 becomes partially transformed into muscular work ; and secondly, 

 that the food does not require to become organized tissue before 

 its metamorphosis can be rendered available for muscular power, 

 its digestion and assimilation into the circulating fluid (the 

 blood) being all that is necessary for this purpose. It is, how- 

 ever, by no means the non-nitrogenous portions of food alone 

 that are capable of being so employed — the nitrogenous also, in- 

 asmuch as they are combustible, and consequently capable of 

 furnishing actual energy, might be expected to be available for 

 the same purpose ; and such an expectation is confirmed by the 

 experiments of Savory upon rats*, which show that these animals 

 can live for weeks in good health upon food consisting almost 

 exclusively of muscular fibre. Even supposing these rats to 

 have performed no external work, nearly the whole of their in- 

 ternal muscular work must have had its source in the actual 

 energy developed by the oxidation of their strictly nitrogenous 

 food. 



It can scarcely be doubted, however, that the chief use of the 

 nitrogenous constituents of food is for the renewal of muscular 

 tissue — the latter, like 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 muscular 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 oxi- 

 dation. The potential energy becomes actual energy, one por- 

 tion assuming the form of motion, another appearing as heat. 

 Here is the source of animal heat, 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 re- 

 newal ; but neither contributes in any important degree, by its 

 own oxidation, to the actual production of the mechanical power 

 which it exerts. 



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 muscular power. I have therefore made careful 

 estimations of the calorific value of different materials used as 

 food, with the same apparatus and in the same manner as described 

 above for the determination of the actual energy in muscle, urea, 

 &c. The results are embodied in the following series of Tables ; 



* The Lancet, 1863, pages 381 and 412. 



