1867.] Food as a Motive Power. 339 



what was already untenable ; for, even apart from the researches 

 already mentioned, Donders had, in a masterly essay published in 

 1864,* proved its insufficiency. Fick and Wislicenus indeed feel 

 themselves justified in adopting the hypothesis of Traube, but this 

 is not a necessary result of their experiment. 



We have before us therefore two opposite views of the origin of 

 muscular power. One has been already shown to be in its entirety 

 untenable, but are we therefore to conclude, as Fick and Wislicenus 

 have done, that the other is necessarily true ? Most important con- 

 sequences hinge upon the answer to the question, for if the view so 

 long accepted be incorrect, all our notions of dietetics must be 

 revised. 



The first argument which is brought against the new hypothesis 

 is founded upon common experience, which certainly seems to teach 

 that a larger quantity of flesh-formers is necessary in the food when 

 extra work is done. The superior strength of the British navvy is 

 usually ascribed, not without probability, to the quantity of meat 

 which he eats ; and Donders sagaciously points to the case of the 

 horse, which, as every one knows, may be fed upon grass when in 

 idleness, but must be supplied with oats — a food richer in flesh- 

 formers — if hard work is expected of him. Without assigning too 

 high a value to arguments of this kind, it must be admitted that 

 they are not destitute of force, and that it is somewhat difficult to 

 answer them upon Traube 's view. 



But more cogent arguments are not wanting. In the first place, 

 it is not literally true that muscular work produces no alteration in 

 the amount of nitrogen excreted ; on the contrary, a small though 

 irregular increase is always noted, a fact which has been confirmed 

 within the present year by some well conducted experiments of Dr. 

 Parkes's.f It is indeed difficult, as Donders remarks, to imagine how 

 it could be otherwise in many cases, for some animals may be fed, as 

 Pettenkoffer and Yoit fed a dog, and Savory, rats, upon food containing 

 nothing but flesh-formers. In such cases the extra- work being done 

 at the expense of nitrogenous food, must be attended with increased 

 excretion of nitrogen. Moreover, it has been shown by numerous 

 experimenters that the disintegration of muscular tissue is always 

 increased by muscular work. Creatin, creatinine, lactic acid, and 

 sugar, all of them products of the decomposition of muscle, have 

 been found to be present in more than the usual quantity in a 

 muscle which has been repeatedly contracted. Very nearly the 

 whole of these substances are oxidized in the body into carbonic acid, 

 water, and urea. It is therefore argued that the oxidation of 

 muscle is as likely to contribute to the motive power of the muscle 



* Translated in ' Dublin Quarterly Journal of Medical Science,' February and 

 May, 1866. 



t ' Proceedings of the Eoyal Society,' Jan. 1867. 



