THE SOURCE OF MUSCULAR POWER. 813 



energy equivalent to that which coiled it. One of the forms which 

 this energy takes on is that of muscular motion, which we thus trace 

 back to the potential energy of food, and through this to that great 

 source of all energy to our earth, the sun. 



We are not, however, satisfied with knowing in this general way 

 that it is the food we eat which serves as a vehicle to convey to us our 

 needful supply of sun-force. We were already acquainted with the 

 necessity for food, but we wish to know which of the ingredients of 

 our food performs this function, or, if all do it, which one performs it 

 to the best advantage. 



Until a comparatively recent date it was assumed unhesitatingly 

 that the albuminoids that is, bodies like albumen (white of egg), fibrine 

 (muscular fiber), caseine (the basis of cheese), etc., which contain the 

 element nitrogen as a characteristic ingredient, and which we shall 

 designate collectively as proteine were the proximate source of mus- 

 cular power. It was taught that work was performed by means of an 

 increased oxidation of the fibrine, of which the muscles are largely 

 composed, and that the proteine of the food served to repair the wear 

 thus caused. This view is still found in many especially of the smaller 

 text-books of physiology, and seems to be the one generally current. 

 Even so eminent a physiologist as Professor Austin Flint, Jr., has 

 recently devoted a small book ("The Source of Muscular Power," 

 D. Appleton & Co., 1878) to its defense ; but nevertheless it was never 

 founded upon experimental evidence, and has now been rendered un- 

 tenable in its original form. 



Karl Voit, of Munich, was the first to make exact experiments on 

 this subject, and in 1860 he published the results of his researches, 

 which showed conclusively that, contrary to the then generally ac- 

 cepted theory, muscular exertion did not increase in the least the 

 amount of proteine decomposed in the body, although it was accom- 

 panied by a large increase in the amount of non-nitrogenous matters 

 oxidized. This fact was immediately accepted by many physiologists 

 as a proof that the commonly received view of the source of muscular 

 power was incorrect, and that that power was in reality derived from 

 the non-nitrogenous components of food its fat, starch, sugar, etc. 

 According to them, the muscles are, like a steam-engine, simply an ap- 

 paratus for the transmission of energy furnished by some other sub- 

 stance, while the fat, etc., is the fuel of the living machine. 



Voit and his followers, on the contrary, still hold that proteine is 

 the proximate source of muscular power, though their views have 

 naturally been materially modified by the experimental results just 

 mentioned. 



Voit compares the constant decomposition of proteine which goes 

 on in the body to the constant flow of water in a stream. A mill 

 situated by the stream may use the whole power of the water, a half, 

 a quarter, or any desired fraction, without in the least altering the 



