486 Drs. A. Fick and J. Wislicenus on the 



specially the oxidation of albuminous compounds which produces 

 muscular force. It is quite possible that the non-nitrogenous 

 substances in muscle play the part of combustibles, although 

 but a small quantity of those substances is to be found in muscle 

 at any particular moment. It is even conceivable that these 

 compounds pass, as it were, through the muscle in a rapid stream, 

 each particle which enters it being immediately oxidized and 

 carried away again. If we examine this supposition more closely, 

 we find that, even from the most general points of view, there 

 is much to be said for the hypothesis that non-nitrogenous 

 compounds form the fuel or oxidizable materials in the muscles. 

 Liebig long ago pointed out that the non-nitrogenous organic 

 compounds of the food, particularly the hydrates of carbon and 

 the fats, are the sources of heat. He, indeed, could hardly have 

 thought of fuel generating mechanical power, chiefly because 

 our present problem was far beyond the chemists and physiolo- 

 gists of that time. But from the point to which science has at 

 present attained, if once a certain group of materials of food 

 are found to be heat-producers, it is easy to conceive the derivation 

 from the oxidation of these substances, not merely of heat, but 

 also of the mechanical work of the organism, since, as is now well 

 known, heat and mechanical work are only two manifestations 

 of the same force. In fact it would be very strange if, in the 

 animal economy, one particular group of food-constituents was 

 used merely for the production of heat, in order that the tem- 

 perature of the body might be maintained above that of the 

 surrounding medium. No doubt this animal warmth is a neces- 

 sary condition of existence for mammals and birds; but the 

 mechanical theory of heat teaches that the almost inevitable se- 

 condary result of the production of muscular work must be heat, 

 and that therefore no special processes are necessary to raise the 

 temperature of the organism, the latter, in fact, going hand in 

 hand with the production of mechanical power. If the non- 

 nitrogenous compounds were exclusively heat-producers in the 

 narrower sense, and the albuminoid bodies, on the contrary, 

 only force- producing material, nature would have proceeded as 

 uneconomically as a manufacturer who should put up a stove 

 near a steam-engine, although a sufficient amount of heat was 

 given out by the steam-engine itself. Although at present, in 

 the light of Darwin's theory, the employment of teleological ar- 

 guments in a certain order of cases has once more become ad- 

 missible, yet we are far from being of opinion that a chemico- 

 physiological question like the above is capable of being decided 

 by such arguments. Nevertheless considerations of this nature 

 may serve to shake other hypotheses which rest only on a tele- 

 ological basis. 



